Sir J. Lubbock's gamekeeper has repeatedly shot, but how many times he

could not say, one of a pair of jays (_Garrulus glandarius_), and has

never failed shortly afterwards to find the survivor rematched. The Rev.

W. D. Fox, Mr. F. Bond, and others, have shot one of a pair of

carrion-crows (_Corvus corone_), but the nest was soon again tenanted by

a pair. These birds are rather common; but the peregrine falcon (_Falco

peregrinus_) is rare, yet Mr. Thompson states that in Ireland "if either

an old male or female be killed in the breeding-season (not an uncommon

circumstance), another mate is found within a very few days, so that the

eyries, notwithstanding such casualties, are sure to turn out their

complement of young." Mr. Jenner Weir has known the same thing to occur

with the peregrine falcons at Beachy Head. The same observer informs me

that three kestrels, all males (_Falco tinnunculus_), were killed one

after the other whilst attending the same nest; two of these were in

mature plumage, and the third in the plumage of the previous year. Even

with the rare golden eagle (_Aquila chrysaetos_), Mr. Birkbeck was

assured by a trustworthy gamekeeper in Scotland, that if one is killed,

another is soon found. So with the white owl (_Strix flammea_), it has

been observed that "the survivor readily found a mate, and the mischief

went on."

White of Selborne, who gives the case of the owl, adds that he knew a

man, who from believing that partridges when paired were disturbed by

the males fighting, used to shoot them; and though he had widowed the

same female several times she was always soon provided with a fresh

partner. This same naturalist ordered the sparrows, which deprived the

house-martins of their nests, to be shot: but the one which was left,

"be it cock or hen, presently procured a mate, and so for several times

following." I could add analogous cases relating to the chaffinch,

nightingale, and redstart. With respect to the latter bird

(_Phoenicura ruticilla_), the writer remarks that it was by no means

common in the neighbourhood, and he expresses much surprise how the

sitting female could so soon give effectual notice that she was a widow.

Mr. Jenner Weir has mentioned to me a nearly similar case: at Blackheath

he never sees or hears the note of the wild bullfinch, yet when one of

his caged males has died, a wild one in the course of a few days has

generally come and perched near the widowed female, whose call-note is

far from loud. I will give only one other fact, on the authority of this

same observer; one of a pair of starlings (_Sturnus vulgaris_) was shot

in the morning; by noon a new mate was found; this was again shot, but

before night the pair was complete; so that the disconsolate widow or

widower was thrice consoled during the same day. Mr. Engleheart also

informs me that he used during several years to shoot one of a pair of

starlings which built in a hole in a house at Blackheath; but the loss

was always immediately repaired. During one season he kept an account

and found that he had shot thirty-five birds from the same nest; these

consisted of both males and females, but in what proportion he could not

say: nevertheless after all this destruction, a brood was reared.[153]

These facts are certainly remarkable. How is it that so many birds are

ready immediately to replace a lost mate? Magpies, jays, carrion-crows,

partridges, and some other birds, are never seen during the spring by

themselves, and these offer at first sight the most perplexing case. But

birds of the same sex, although of course not truly paired, sometimes

live in pairs or in small parties, as is known to be the case with

pigeons and partridges. Birds also sometimes live in triplets, as has

been observed with starlings, carrion-crows, parrots, and partridges.

With partridges two females have been known to live with one male, and

two males with one female. In all such cases it is probable that the

union would be easily broken. The males of certain birds may

occasionally be heard pouring forth their love-song long after the

proper time, shewing that they have either lost or never gained a mate.

Death from accident or disease of either one of a pair, would leave the

other bird free and single; and there is reason to believe that female

birds during the breeding-season are especially liable to premature

death. Again, birds which have had their nests destroyed, or barren

pairs, or retarded individuals, would easily be induced to desert their

mates, and would probably be glad to take what share they could of the

pleasures and duties of rearing offspring, although not their own.[154]

Such contingencies as these probably explain most of the foregoing

cases.[155] Nevertheless it is a strange fact that within the same

district, during the height of the breeding-season, there should be so

many males and females always ready to repair the loss of a mated bird.

Why do not such spare birds immediately pair together? Have we not some

reason to suspect, and the suspicion has occurred to Mr. Jenner Weir,

that inasmuch as the act of courtship appears to be with many birds a

prolonged and tedious affair, so it occasionally happens that certain

males and females do not succeed during the proper season, in exciting

each other's love, and consequently do not pair? This suspicion will

appear somewhat less improbable after we have seen what strong

antipathies and preferences female birds occasionally evince towards

particular males.

_Mental Qualities of Birds, and their taste for the beautiful._--Before

we discuss any further the question whether the females select the more

attractive males or accept the first whom they may encounter, it will be

advisable briefly to consider the mental powers of birds. Their reason

is generally, and perhaps justly, ranked as low; yet some facts could be

given[156] leading to an opposite conclusion. Low powers of reasoning,

however, are compatible, as we see with mankind, with strong affections,

acute perception, and a taste for the beautiful; and it is with these

latter qualities that we are here concerned. It has often been said that

parrots become so deeply attached to each other that when one dies the

other for a long time pines; but Mr. Jenner Weir thinks that with most

birds the strength of their affection has been much exaggerated.

Nevertheless when one of a pair in a state of nature has been shot, the

survivor has been heard for days afterwards uttering a plaintive call;

and Mr. St. John gives[157] various facts proving the attachment of

mated birds. Starlings, however, as we have seen, may be consoled thrice

in the same day for the loss of their mates. In the Zoological Gardens

parrots have clearly recognised their former masters after an interval

of some months. Pigeons have such excellent local memories that they

have been known to return to their former homes after an interval of

nine months, yet, as I hear from Mr. Harrison Weir, if a pair which

would naturally remain mated for life be separated for a few weeks

during the winter and matched with other birds, the two, when brought

together again, rarely, if ever, recognise each other.

Birds sometimes exhibit benevolent feelings; they will feed the deserted

young even of distinct species, but this perhaps ought to be considered

as a mistaken instinct. They will also feed, as shewn in an earlier part

of this work, adult birds of their own species which have become blind.

Mr. Buxton gives a curious account of a parrot which took care of a

frost-bitten and crippled bird of a distinct species, cleansed her

feathers and defended her from the attacks of the other parrots which

roamed freely about his garden. It is a still more curious fact that

these birds apparently evince some sympathy for the pleasures of their

fellows. When a pair of cockatoos made a nest in an acacia tree, "it was

ridiculous to see the extravagant interest taken in the matter by the

others of the same species." These parrots, also, evinced unbounded

curiosity, and clearly had "the idea of property and possession."[158]

Birds possess acute powers of observation. Every mated bird, of course,

recognises its fellow. Audubon states that with the mocking-thrushes of

the United States (_Mimus polyglottus_) a certain number remain all the

year round in Louisiana, whilst the others migrate to the Eastern

States; these latter, on their return, are instantly recognised, and

always attacked, by their Southern brethren. Birds under confinement

distinguish different persons, as is proved by the strong and permanent

antipathy or affection which they shew, without any apparent cause,

towards certain individuals. I have heard of numerous instances with

jays, partridges, canaries, and especially bullfinches. Mr. Hussey has

described in how extraordinary a manner a tamed partridge recognised

everybody; and its likes and dislikes were very strong. This bird seemed

"fond of gay colours, and no new gown or cap could be put on without

catching his attention."[159] Mr. Hewitt has carefully described the

habits of some ducks (recently descended from wild birds), which, at the

approach of a strange dog or cat, would rush headlong into the water,

and exhaust themselves in their attempts to escape; but they knew so

well Mr. Hewitt's own dogs and cats that they would lie down and bask in

the sun close to them. They always moved away from a strange man, and so

they would from the lady who attended them, if she made any great change

in her dress. Audubon relates that he reared and tamed a wild turkey

which always ran away from any strange dog; this bird escaped into the

woods, and some days afterwards Audubon saw, as he thought, a wild

turkey, and made his dog chase it; but to his astonishment, the bird did

not run away, and the dog, when he came up, did not attack the bird, for

they mutually recognised each other as old friends.[160]

Mr. Jenner Weir is convinced that birds pay particular attention to the

colours of other birds, sometimes out of jealousy, and sometimes as a

sign of kinship. Thus he turned a reed-bunting (_Emberiza

schoeniculus_), which had acquired its black head, into his aviary,

and the new-comer was not noticed by any bird, except by a bullfinch,

which is likewise black-headed. This bullfinch was a very quiet bird,

and had never before quarrelled with any of its comrades, including

another reed-bunting, which had not as yet become black-headed: but the

reed-bunting with a black head was so unmercifully treated, that it had

to be removed. Mr. Weir was also obliged to turn out a robin, as it

fiercely attacked all birds with any red in their plumage, but no other

kinds; it actually killed a red-breasted crossbill, and nearly killed a

goldfinch. On the other hand, he has observed that some birds, when

first introduced into his aviary, fly towards the species which resemble

them most in colour, and settle by their sides.

As male birds display with so much care their fine plumage and other

ornaments in the presence of the females, it is obviously probable that

these appreciate the beauty of their suitors. It is, however, difficult

to obtain direct evidence of their capacity to appreciate beauty. When

birds gaze at themselves in a looking-glass (of which many instances

have been recorded) we cannot feel sure that it is not from jealousy at

a supposed rival, though this is not the conclusion of some observers.

In other cases it is difficult to distinguish between mere curiosity and

admiration. It is perhaps the former feeling which, as stated by Lord

Lilford,[161] attracts the Ruff strongly towards any bright object, so

that, in the Ionian Islands, it "will dart down to a bright-coloured

handkerchief, regardless of repeated shots." The common lark is drawn

down from the sky, and is caught in large numbers, by a small mirror

made to move and glitter in the sun. Is it admiration or curiosity which

leads the magpie, raven, and some other birds to steal and secrete

bright objects, such as silver articles or jewels?

Mr. Gould states that certain humming-birds decorate the outside of

their nests, "with the utmost taste; they instinctively fasten thereon

beautiful pieces of flat lichen, the larger pieces in the middle, and

the smaller on the part attached to the branch. Now and then a pretty

feather is intertwined or fastened to the outer sides, the stem being

always so placed, that the feather stands out beyond the surface." The

best evidence, however, of a taste for the beautiful is afforded by the

three genera of Australian bower-birds already mentioned. Their bowers

(see fig. 46, p. 70), where the sexes congregate and play strange

antics, are differently constructed, but what most concerns us is, that

they are decorated in a different manner by the several species. The

Satin bower-bird collects gaily-coloured articles, such as the blue

tail-feathers of parrakeets, bleached bones and shells, which it sticks

between the twigs, or arranges at the entrance. Mr. Gould found in one

bower a neatly-worked stone tomahawk and a slip of blue cotton,

evidently procured from a native encampment. These objects are

continually rearranged, and carried about by the birds whilst at play.

The bower of the Spotted bower-bird "is beautifully lined with tall

grasses, so disposed that the heads nearly meet, and the decorations are

very profuse." Round stones are used to keep the grass-stems in their

proper places, and to make divergent paths leading to the bower. The

stones and shells are often brought from a great distance. The Regent

bird, as described by Mr. Ramsay, ornaments its short bower with

bleached land-shells belonging to five or six species, and with "berries

of various colours, blue, red, and black, which give it when fresh a

very pretty appearance. Besides these there were several newly-picked

leaves and young shoots of a pinkish colour, the whole shewing a decided

taste for the beautiful." Well may Mr. Gould say "these highly decorated

halls of assembly must be regarded as the most wonderful instances of

bird-architecture yet discovered;" and the taste, as we see, of the

several species certainly differs.[162]

_Preference for particular Males by the Females._--Having made these

preliminary remarks on the discrimination and taste of birds, I will

give all the facts known to me, which bear on the preference shewn by

the female for particular males. It is certain that distinct species of

birds occasionally pair in a state of nature and produce hybrids. Many

instances could be given: thus Macgillivray relates how a male blackbird

and female thrush "fell in love with each other," and produced

offspring.[163] Several years ago eighteen cases had been recorded of

the occurrence in Great Britain of hybrids between the black grouse and

pheasant;[164] but most of these cases may perhaps be accounted for by

solitary birds not finding one of their own species to pair with. With

other birds, as Mr. Jenner Weir has reason to believe, hybrids are

sometimes the result of the casual intercourse of birds building in

close proximity. But these remarks do not apply to the many recorded

instances of tamed or domestic birds, belonging to distinct species,

which have become absolutely fascinated with each other, although living

with their own species. Thus Waterton[165] states that out of a flock of

twenty-three Canada geese, a female paired with a solitary Bernicle

gander, although so different in appearance and size; and they produced

hybrid offspring. A male Wigeon (_Mareca penelope_), living with females

of the same species, has been known to pair with a Pintail duck,

_Querquedula acuta_. Lloyd describes the remarkable attachment between a

shield-drake (_Tadorna vulpanser_) and a common duck. Many additional

instances could be given; and the Rev. E. S. Dixon remarks that "Those

who have kept many different species of geese together, well know what

unaccountable attachments they are frequently forming, and that they are

quite as likely to pair and rear young with individuals of a race

(species) apparently the most alien to themselves, as with their own

stock."

The Rev. W. D. Fox informs me that he possessed at the same time a pair

of Chinese geese (_Anser cygnoides_), and a common gander with three

geese. The two lots kept quite separate, until the Chinese gander

seduced one of the common geese to live with him. Moreover, of the young

birds hatched from the eggs of the common geese, only four were pure,

the other eighteen proving hybrids; so that the Chinese gander seems to

have had prepotent charms over the common gander. I will give only one

other case; Mr. Hewitt states that a wild duck, reared in captivity,

"after breeding a couple of seasons with her own mallard, at once shook

him off on my placing a male Pintail on the water. It was evidently a

case of love at first sight, for she swam about the new-comer

caressingly, though he appeared evidently alarmed and averse to her

overtures of affection. From that hour she forgot her old partner.

Winter passed by, and the next spring the Pintail seemed to have become

a convert to her blandishments, for they nested and produced seven or

eight young ones."

What the charm may have been in these several cases, beyond mere

novelty, we cannot even conjecture. Colour, however, sometimes comes

into play; for in order to raise hybrids from the siskin (_Fringilla

spinus_) and the canary, it is much the best plan, according to

Bechstein, to place birds of the same tint together. Mr. Jenner Weir

turned a female canary into his aviary, where there were male linnets,

goldfinches, siskins, greenfinches, chaffinches, and other birds, in

order to see which she would choose; but there never was any doubt, and

the greenfinch carried the day. They paired and produced hybrid

offspring.

With the members of the same species the fact of the female preferring

to pair with one male rather than with another is not so likely to

excite attention, as when this occurs between distinct species. Such

cases can best be observed with domesticated or confined birds; but

these are often pampered by high feeding, and sometimes have their

instincts vitiated to an extreme degree. Of this latter fact I could

give sufficient proofs with pigeons, and especially with fowls, but they

cannot be here related. Vitiated instincts may also account for some of

the hybrid unions above referred to; but in many of these cases the

birds were allowed to range freely over large ponds, and there is no

reason to suppose that they were unnaturally stimulated by high feeding.

With respect to birds in a state of nature, the first and most obvious

supposition which will occur to everyone is that the female at the

proper season accepts the first male whom she may encounter; but she has

at least the opportunity for exerting a choice, as she is almost

invariably pursued by many males. Audubon--and we must remember that he

spent a long life in prowling about the forests of the United States and

observing the birds--does not doubt that the female deliberately chooses

her mate; thus, speaking of a woodpecker, he says the hen is followed by

half-a-dozen gay suitors, who continue performing strange antics, "until

a marked preference is shewn for one." The female of the red-winged

starling (_Agelaeus phoeniceus_) is likewise pursued by several males,

"until, becoming fatigued, she alights, receives their addresses, and

soon makes a choice." He describes also how several male nightjars

repeatedly plunge through the air with astonishing rapidity, suddenly

turning, and thus making a singular noise; "but no sooner has the female

made her choice, than the other males are driven away." With one of the

vultures (_Cathartes aura_) of the United States, parties of eight or

ten or more males and females assemble on fallen logs, "exhibiting the

strongest desire to please mutually," and after many caresses, each male

leads off his partner on the wing. Audubon likewise carefully observed

the wild flocks of Canada geese (_Anser Canadensis_), and gives a

graphic description of their love-antics; he says that the birds which

had been previously mated "renewed their courtship as early as the month

of January, while the others would be contending or coquetting for

hours every day, until all seemed satisfied with the choice they had

made, after which, although they remained together, any person could

easily perceive that they were careful to keep in pairs. I have observed

also that the older the birds, the shorter were the preliminaries of

their courtship. The bachelors and old maids, whether in regret, or not

caring to be disturbed by the bustle, quietly moved aside and lay down

at some distance from the rest."[166] Many similar statements with

respect to other birds could be cited from this same observer.

Turning now to domesticated and confined birds, I will commence by

giving what little I have learnt respecting the courtship of fowls. I

have received long letters on this subject from Messrs. Hewitt and

Tegetmeier, and almost an essay from the late Mr. Brent. It will be

admitted by every one that these gentlemen, so well known from their

published works, are careful and experienced observers. They do not

believe that the females prefer certain males on account of the beauty

of their plumage; but some allowance must be made for the artificial

state under which they have long been kept. Mr. Tegetmeier is convinced

that a game-cock, though disfigured by being dubbed with his hackles

trimmed, would be accepted as readily as a male retaining all his

natural ornaments. Mr. Brent, however, admits that the beauty of the

male probably aids in exciting the female; and her acquiescence is

necessary. Mr. Hewitt is convinced that the union is by no means left to

mere chance, for the female almost invariably prefers the most vigorous,

defiant, and mettlesome male; hence it is almost useless, as he remarks,

"to attempt true breeding if a game-cock in good health and condition

runs the locality, for almost every hen on leaving the roosting-place

will resort to the game-cock, even though that bird may not actually

drive away the male of her own variety." Under ordinary circumstances

the males and females of the fowl seem to come to a mutual understanding

by means of certain gestures, described to me by Mr. Brent. But hens

will often avoid the officious attentions of young males. Old hens, and

hens of a pugnacious disposition, as the same writer informs me, dislike

strange males, and will not yield until well beaten into compliance.

Ferguson, however, describes how a quarrelsome hen was subdued by the

gentle courtship of a Shanghai cock.[167]

There is reason to believe that pigeons of both sexes prefer pairing

with birds of the same breed; and dovecot-pigeons dislike all the highly

improved breeds.[168] Mr. Harrison Weir has lately heard from a

trustworthy observer, who keeps blue pigeons, that these drive away all

other coloured varieties, such as white, red, and yellow; and from

another observer, that a female dun carrier could not be matched, after

repeated trials, with a black male, but immediately paired with a dun.

Generally colour alone appears to have little influence on the pairing

of pigeons. Mr. Tegetmeier, at my request, stained some of his birds

with magenta, but they were not much noticed by the others.

Female pigeons occasionally feel a strong antipathy towards certain

males, without any assignable cause. Thus MM. Boitard and Corbie, whose

experience extended over forty-five years, state: "Quand une femelle

eprouve de l'antipathie pour un male avec lequel on veut l'accoupler,

malgre tous les feux de l'amour, malgre l'alpiste et le chenevis dont on

la nourrit pour augmenter son ardeur, malgre un emprisonnement de six

mois et meme d'un an, elle refuse constamment ses caresses; les avances

empressees, les agaceries, les tournoiemens, les tendres roucoulemens,

rien ne peut lui plaire ni l'emouvoir; gonflee, boudeuse, blottie dans

un coin de sa prison, elle n'en sort que pour boire et manger, ou pour

repousser avec une espece de rage des caresses devenues trop

pressantes."[169] On the other hand, Mr. Harrison Weir has himself

observed, and has heard from, several breeders, that a female pigeon

will occasionally take a strong fancy for a particular male, and will

desert her own mate for him. Some females, according to another

experienced observer, Riedel,[170] are of a profligate disposition, and

prefer almost any stranger to their own mate. Some amorous males, called

by our English fanciers "gay birds," are so successful in their

gallantries, that, as Mr. H. Weir informs me, they must be shut up, on

account of the mischief which they cause.

Wild turkeys in the United States, according to Audubon, "sometimes pay

their addresses to the domesticated females, and are generally received

by them with great pleasure." So that these females apparently prefer

the wild to their own males.[171]

Here is a more curious case. Sir R. Heron during many years kept an

account of the habits of the peafowl, which he bred in large numbers. He

states that "the hens have frequently great preference to a particular

peacock. They were all so fond of an old pied cock, that one year, when

he was confined though still in view, they were constantly assembled

close to the trellice-walls of his prison, and would not suffer a

japanned peacock to touch them. On his being let out in the autumn, the

oldest of the hens instantly courted him, and was successful in her

courtship. The next year he was shut up in a stable, and then the hens

all courted his rival."[172] This rival was a japanned or black-winged

peacock, which to our eyes is a more beautiful bird than the common

kind.

Lichtenstein, who was a good observer and had excellent opportunities of

observation at the Cape of Good Hope, assured Rudolphi that the female

widow-bird (_Chera progne_) disowns the male, when robbed of the long

tail-feathers with which he is ornamented during the breeding-season. I

presume that this observation must have been made on birds under

confinement.[173] Here is another striking case; Dr. Jaeger,[174]

director of the Zoological Gardens of Vienna, states that a male

silver pheasant, who had been triumphant over the other males and was

the accepted lover of the females, had his ornamental plumage spoiled.

He was then immediately superseded by a rival, who got the upper hand

and afterwards led the flock.

Not only does the female exert a choice, but in some few cases she

courts the male, or even fights for his possession. Sir R. Heron states

that with peafowl, the first advances are always made by the female;

something of the same kind takes place, according to Audubon, with the

older females of the wild turkey. With the capercailzie, the females

flit round the male, whilst he is parading at one of the places of

assemblage, and solicit his attention.[175] We have seen that a tame

wild-duck seduced after a long courtship an unwilling Pintail drake. Mr.

Bartlett believes that the Lophophorus, like many other gallinaceous

birds, is naturally polygamous, but two females cannot be placed in the

same cage with a male, as they fight so much together. The following

instance of rivalry is more surprising as it relates to bullfinches,

which usually pair for life. Mr. Jenner Weir introduced a dull-coloured

and ugly female into his aviary, and she immediately attacked another

mated female so unmercifully that the latter had to be separated. The

new female did all the courtship, and was at last successful, for she

paired with the male; but after a time she met with a just retribution,

for, ceasing to be pugnacious, Mr. Weir replaced the old female, and the

male then deserted his new and returned to his old love.

In all ordinary cases the male is so eager that he will accept any

female, and does not, as far as we can judge, prefer one to the other;

but exceptions to this rule, as we shall hereafter see, apparently occur

in some few groups. With domesticated birds, I have heard of only one

case in which the males shew any preference for particular females,

namely, that of the domestic cock, who, according to the high authority

of Mr. Hewitt, prefers the younger to the older hens. On the other

hand, in effecting hybrid unions between the male pheasant and common

hens, Mr. Hewitt is convinced that the pheasant invariably prefers the

older birds. He does not appear to be in the least influenced by their

colour, but "is most capricious in his attachments."[176] From some

inexplicable cause he shews the most determined aversion to certain

hens, which no care on the part of the breeder can overcome. Some hens,

as Mr. Hewitt informs me, are quite unattractive even to the males of

their own species, so that they may be kept with several cocks during a

whole season, and not one egg out of forty or fifty will prove fertile.

On the other hand with the Long-tailed duck (_Harelda glacialis_), "it

has been remarked," says M. Ekstroem, "that certain females are much more

courted than the rest. Frequently, indeed, one sees an individual

surrounded by six or eight amorous males." Whether this statement is

credible, I know not; but the native sportsmen shoot these females in

order to stuff them as decoys.[177]

With respect to female birds feeling a preference for particular males,

we must bear in mind that we can judge of choice being exerted, only by

placing ourselves in imagination in the same position. If an inhabitant

of another planet were to behold a number of young rustics at a fair,

courting and quarrelling over a pretty girl, like birds at one of their

places of assemblage, he would be able to infer that she had the power

of choice only by observing the eagerness of the wooers to please her,

and to display their finery. Now with birds, the evidence stands thus;

they have acute powers of observation, and they seem to have some taste

for the beautiful both in colour and sound. It is certain that the

females occasionally exhibit, from unknown causes, the strongest

antipathies and preferences for particular males. When the sexes differ

in colour or in other ornaments, the males with rare exceptions are the

most highly decorated, either permanently or temporarily during the

breeding-season. They sedulously display their various ornaments, exert

their voices, and perform strange antics in the presence of the females.

Even well-armed males, who, it might have been thought, would have

altogether depended for success on the law of battle, are in most cases

highly ornamented; and their ornaments have been acquired at the expense

of some loss of power. In other cases ornaments have been acquired, at

the cost of increased risk from birds and beasts of prey. With various

species many individuals of both sexes congregate at the same spot, and

their courtship is a prolonged affair. There is even reason to suspect

that the males and females within the same district do not always

succeed in pleasing each other and pairing.

What then are we to conclude from these facts and considerations? Does

the male parade his charms with so much pomp and rivalry for no purpose?

Are we not justified in believing that the female exerts a choice, and

that she receives the addresses of the male who pleases her most? It is

not probable that she consciously deliberates; but she is most excited

or attracted by the most beautiful, or melodious, or gallant males. Nor

need it be supposed that the female studies each stripe or spot of

colour; that the peahen, for instance, admires each detail in the

gorgeous train of the peacock--she is probably struck only by the

general effect. Nevertheless after hearing how carefully the male Argus

pheasant displays his elegant primary wing-feathers, and erects his

ocellated plumes in the right position for their full effect; or again,

how the male goldfinch alternately displays his gold-bespangled wings,

we ought not to feel too sure that the female does not attend to each

detail of beauty. We can judge, as already remarked, of choice being

exerted, only from the analogy of our own minds; and the mental powers

of birds, if reason be excluded, do not fundamentally differ from ours.

From these various considerations we may conclude that the pairing of

birds is not left to chance; but that those males, which are best able

by their various charms to please or excite the female, are under

ordinary circumstances accepted. If this be admitted, there is not much

difficulty in understanding how male birds have gradually acquired their

ornamental characters. All animals present individual differences, and

as man can modify his domesticated birds by selecting the individuals

which appear to him the most beautiful, so the habitual or even

occasional preference by the female of the more attractive males would

almost certainly lead to their modification; and such modifications

might in the course of time be augmented to almost any extent,

compatible with the existence of the species.

_Variability of Birds, and especially of their secondary Sexual

Characters._--Variability and inheritance are the foundations for the

work of selection. That domesticated birds have varied greatly, their

variations being inherited, is certain. That birds in a state of nature

present individual differences is admitted by every one; and that they

have sometimes been modified into distinct races, is generally

admitted.[178] Variations are of two kinds, which insensibly graduate

into each other, namely, slight differences between all the members of

the same species, and more strongly-marked deviations which occur only

occasionally. These latter are rare with birds in a state of nature, and

it is very doubtful whether they have often been preserved through

selection, and then transmitted to succeeding generations.[179]

Nevertheless, it may be worth while to give the few cases relating

chiefly to colour (simple albinism and melanism being excluded), which I

have been able to collect.

Mr. Gould is well known rarely to admit the existence of varieties, for

he esteems very slight differences as specific; now he states[180] that

near Bogota certain humming-birds belonging to the genus Cynanthus are

divided into two or three races or varieties, which differ from each

other in the colouring of the tail,--"some having the whole of the

feathers blue, while others have the eight central ones tipped with

beautiful green." It does not appear that intermediate gradations have

been observed in this or the following cases. In the males alone of one

of the Australian parrakeets "the thighs in some are scarlet, in others

grass-green." In another parrakeet of the same country "some individuals

have the band across the wing-coverts bright-yellow, while in others the

same part is tinged with red."[181] In the United States some few of the

males of the Scarlet Tanager (_Tanagra rubra_) have "a beautiful

transverse band of glowing red on the smaller wing-coverts;"[182] but

this variation seems to be somewhat rare, so that its preservation

through sexual selection would follow only under unusually favourable

circumstances. In Bengal the Honey buzzard (_Pernis cristata_) has

either a small rudimental crest on its head, or none at all; so slight a

difference however would not have been worth notice, had not this same

species possessed in Southern India "a well-marked occipital crest

formed of several graduated feathers."[183]

The following case is in some respects more interesting. A pied variety

of the raven, with the head, breast, abdomen, and parts of the wings and

tail-feathers white, is confined to the Feroe Islands. It is not very

rare there, for Graba saw during his visit from eight to ten living

specimens. Although the characters of this variety are not quite

constant, yet it has been named by several distinguished ornithologists

as a distinct species. The fact of the pied birds being pursued and

persecuted with much clamour by the other ravens of the island was the

chief cause which led Bruennich to conclude that it was specifically

distinct; but this is now known to be an error.[184]

In various parts of the northern seas a remarkable variety of the common

Guillemot (_Uria troile_) is found; and in Feroe, one out of every five

birds, according to Graba's estimation, consists of this variety. It is

characterised[185] by a pure white ring round the eye, with a curved

narrow white line, an inch and a half in length, extending back from the

ring. This conspicuous character has caused the bird to be ranked by

several ornithologists as a distinct species under the name of _U.

lacrymans_, but it is now known to be merely a variety. It often pairs

with the common kind, yet intermediate gradations have never been seen;

nor is this surprising, for variations which appear suddenly are often,

as I have elsewhere shewn,[186] transmitted either unaltered or not at

all. We thus see that two distinct forms of the same species may

co-exist in the same district, and we cannot doubt that if the one had

possessed any great advantage over the other, it would soon have been

multiplied to the exclusion of the latter. If, for instance, the male

pied ravens, instead of being persecuted and driven away by their

comrades, had been highly attractive, like the pied peacock before

mentioned, to the common black females, their numbers would have rapidly

increased. And this would have been a case of sexual selection.

With respect to the slight individual differences which are common, in

a greater or less degree, to all the members of the same species, we

have every reason to believe that they are by far the most important for

the work of selection. Secondary sexual characters are eminently liable

to vary, both with animals in a state of nature and under

domestication.[187] There is also reason to believe, as we have seen in

our eighth chapter, that variations are more apt to occur in the male

than in the female sex. All these contingencies are highly favourable

for sexual selection. Whether characters thus acquired are transmitted

to one sex or to both sexes, depends exclusively in most cases, as I

hope to shew in the following chapter, on the form of inheritance which

prevails in the groups in question.

It is sometimes difficult to form any opinion whether certain slight

differences between the sexes of birds are simply the result of

variability with sexually-limited inheritance, without the aid of sexual

selection, or whether they have been augmented through this latter

process. I do not here refer to the innumerable instances in which the

male displays splendid colours or other ornaments, of which the female

partakes only to a slight degree; for these cases are almost certainly

due to characters primarily acquired by the male, having been

transferred, in a greater or less degree, to the female. But what are we

to conclude with respect to certain birds in which, for instance, the

eyes differ slightly in colour in the two sexes?[188] In some cases the

eyes differ conspicuously; thus with the storks of the genus

_Xenorhynchus_ those of the male are blackish-hazel, whilst those of the

females are gamboge-yellow; with many hornbills (Buceros), as I hear

from Mr. Blyth,[189] the males have intense crimson, and the females

white eyes. In the _Buceros bicornis_, the hind margin of the casque and

a stripe on the crest of the beak are black in the male, but not so in

the female. Are we to suppose that these black marks and the crimson

colour of the eyes have been preserved or augmented through sexual

selection in the males? This is very doubtful; for Mr. Bartlett shewed

me in the Zoological Gardens that the inside of the mouth of this

Buceros is black in the male and flesh-coloured in the female; and their

external appearance or beauty would not be thus affected. I observed in

Chili[190] that the iris in the condor, when about a year old, is

dark-brown, but changes at maturity into yellowish-brown in the male,

and into bright red in the female. The male has also a small,

longitudinal, leaden-coloured, fleshy crest or comb. With many

gallinaceous birds the comb is highly ornamental, and assumes vivid

colours during the act of courtship; but what are we to think of the

dull-coloured comb of the condor, which does not appear to us in the

least ornamental? The same question may be asked in regard to various

other characters, such as the knob on the base of the beak of the

Chinese goose (_Anser cygnoides_), which is much larger in the male than

in the female. No certain answer can be given to these questions; but we

ought to be cautious in assuming that knobs and various fleshy

appendages cannot be attractive to the female, when we remember that

with savage races of man various hideous deformities--deep scars on the

face with the flesh raised into protuberances, the septum of the nose

pierced by sticks or bones, holes in the ears and lips stretched widely

open--are all admired as ornamental.

Whether or not unimportant differences between the sexes, such as those

just specified, have been preserved through sexual selection, these

differences, as well as all others, must primarily depend on the laws of

variation. On the principle of correlated development, the plumage often

varies on different parts of the body, or over the whole body, in the

same manner. We see this well illustrated in certain breeds of the fowl.

In all the breeds the feathers on the neck and loins of the males are

elongated, and are called hackles; now when both sexes acquire a

top-knot, which is a new character in the genus, the feathers on the

head of the male become hackle-shaped, evidently on the principle of

correlation; whilst those on the head of the female are of the ordinary

shape. The colour also of the hackles forming the top-knot of the male,

is often correlated with that of the hackles on the neck and loins, as

may be seen by comparing these feathers in the Golden and

Silver-spangled Polish, the Houdans, and Creve-coeur breeds. In some

natural species we may observe exactly the same correlation in the

colours of these same feathers, as in the males of the splendid Golden

and Amherst pheasants.

The structure of each individual feather generally causes any change in

its colouring to be symmetrical; we see this in the various laced,

spangled, and pencilled breeds of the fowl; and on the principle of

correlation the feathers over the whole body are often modified in the

same manner. We are thus enabled without much trouble to rear breeds

with their plumage marked and coloured almost as symmetrically as in

natural species. In laced and spangled fowls the coloured margins of the

feathers are abruptly defined; but in a mongrel raised by me from a

black Spanish cock glossed with green and a white game hen, all the

feathers were greenish-black, excepting towards their extremities, which

were yellowish-white; but between the white extremities and the black

bases, there was on each feather a symmetrical, curved zone of

dark-brown. In some instances the shaft of the feather determines the

distribution of the tints; thus with the body-feathers of a mongrel from

the same black Spanish cock and a silver-spangled Polish hen, the shaft,

together with a narrow space on each side, was greenish-black, and this

was surrounded by a regular zone of dark-brown, edged with

brownish-white. In these cases we see feathers becoming symmetrically

shaded, like those which give so much elegance to the plumage of many

natural species. I have also noticed a variety of the common pigeon with

the wing-bars symmetrically zoned with three bright shades, instead of

being simply black on a slaty-blue ground, as in the parent-species.

In many large groups of birds it may be observed that the plumage is

differently coloured in each species, yet that certain spots, marks, or

stripes, though likewise differently coloured, are retained by all the

species. Analogous cases occur with the breeds of the pigeon, which

usually retain the two wing-bars, though they may be coloured red,

yellow, white, black, or blue, the rest of the plumage being of some

wholly different tint. Here is a more curious case, in which certain

marks are retained, though coloured in almost an exactly reversed manner

to what is natural; the aboriginal pigeon has a blue tail, with the

terminal halves of the outer webs of the two outer tail-feathers white;

now there is a sub-variety having a white instead of a blue tail,

with precisely that small part black which is white in the

parent-species.[191]

_Formation and variability of the Ocelli or eye-like Spots on the

Plumage of Birds._--As no ornaments are more beautiful than the ocelli

on the feathers of various birds, on the hairy coats of some mammals, on

the scales of reptiles and fishes, on the skin of amphibians, on the

wings of many Lepidoptera and other insects, they deserve to be

especially noticed. An ocellus consists of a spot within a ring of

another colour, like the pupil within the iris, but the central spot is

often surrounded by additional concentric zones. The ocelli on the

tail-coverts of the peacock offer a familiar example, as well as those

on the wings of the peacock-butterfly (Vanessa). Mr. Trimen has given me

a description of a S. African moth (_Gynanisa Isis_), allied to our

Emperor moth, in which a magnificent ocellus occupies nearly the whole

surface of each hinder wing; it consists of a black centre, including a

semi-transparent crescent-shaped mark, surrounded by successive

ochre-yellow, black, ochre-yellow, pink, white, pink, brown, and whitish

zones. Although we do not know the steps by which these wonderfully

beautiful and complex ornaments have been developed, the process at

least with insects has probably been a simple one; for, as Mr. Trimen

writes to me, "no characters of mere marking or coloration are so

unstable in the Lepidoptera as the ocelli, both in number and size." Mr.

Wallace, who first called my attention to this subject, shewed me a

series of specimens of our common meadow-brown butterfly (_Hipparchia

Janira_) exhibiting numerous gradations from a simple minute black spot

to an elegantly-shaded ocellus. In a S. African butterfly (_Cyllo Leda_)

belonging to the same family, the ocelli are even still more variable.

In some specimens (A, fig. 52) large spaces on the upper surface of the

wings are coloured black, and include irregular white marks; and from

this state a complete gradation can be traced into a tolerably perfect

(A^1) ocellus, and this results from the contraction of the irregular

blotches of colour. In another series of specimens a gradation can be

followed from excessively minute white dots, surrounded by a scarcely

visible black line (B), into perfectly symmetrical and large ocelli

(B^1).[192] In cases like these, the development of a perfect ocellus

does not require a long course of variation and selection.

[Illustration: Fig. 52. Cyllo leda, Linn., from a drawing by Mr. Trimen,

shewing the extreme range of variation in the ocelli.

A. Specimen, from Mauritius, upper B. Specimen, from Java, upper

surface of fore-wing. surface of hind-wing.

A^1. Specimen, from Natal, ditto. B^1. Specimen, from Mauritius,

ditto.]

With birds and many other animals it seems, from the comparison of

allied species, to follow, that circular spots are often generated by

the breaking up and contraction of stripes. In the Tragopan pheasant

faint white lines in the female represent the beautiful white spots in

the male;[193] and something of the same kind may be observed in the two

sexes of the Argus pheasant. However this may be, appearances strongly

favour the belief that, on the one hand, a dark spot is often formed by

the colouring-matter being drawn towards a central point from a

surrounding zone, which is thus rendered lighter. And, on the other

hand, that a white spot is often formed by the colour being driven away

from a central point, so that it accumulates in a surrounding darker

zone. In either case an ocellus is the result. The colouring matter

seems to be a nearly constant quantity, but is redistributed, either

centripetally or centrifugally. The feathers of the common guinea-fowl

offer a good instance of white spots surrounded by darker zones; and

wherever the white spots are large and stand near each other, the

surrounding dark zones become confluent. In the same wing-feather of the

Argus pheasant dark spots may be seen surrounded by a pale zone, and

white spots by a dark zone. Thus the formation of an ocellus in its

simplest state appears to be a simple affair. By what further steps the

more complex ocelli, which are surrounded by many successive zones of

colour, have been generated, I will not pretend to say. But bearing

in mind the zoned feathers of the mongrel offspring from

differently-coloured fowls, and the extraordinary variability of the

ocelli in many Lepidoptera, the formation of these beautiful ornaments

can hardly be a highly complex process, and probably depends on some

slight and graduated change in the nature of the tissues.

_Gradation of Secondary Sexual Characters._--Cases of gradation are

important for us, as they shew that it is at least possible that highly

complex ornaments may have been acquired by small successive steps. In

order to discover the actual steps by which the male of any existing

bird has acquired his magnificent colours or other ornaments, we ought

to behold the long line of his ancient and extinct progenitors; but this

is obviously impossible. We may, however, generally gain a clue by

comparing all the species of a group, if it be a large one; for some of

them will probably retain, at least in a partial manner, traces of their

former characters. Instead of entering on tedious details respecting

various groups, in which striking instances of gradation could be given,

it seems the best plan to take some one or two strongly-characterised

cases, for instance that of the peacock, in order to discover if any

light can thus be thrown on the steps by which this bird has become so

splendidly decorated. The peacock is chiefly remarkable from the

extraordinary length of his tail-coverts; the tail itself not being much

elongated. The barbs along nearly the whole length of these feathers

stand separate or are decomposed; but this is the case with the feathers

of many species, and with some varieties of the domestic fowl and

pigeon. The barbs coalesce towards the extremity of the shaft to form

the oval disc or ocellus, which is certainly one of the most beautiful

objects in the world. This consists of an iridescent, intensely blue,

indented centre, surrounded by a rich green zone, and this by a broad

coppery-brown zone, and this by five other narrow zones of

slightly-different iridescent shades. A trifling character in the disc

perhaps deserves notice; the barbs, for a space along one of the

concentric zones are destitute, to a greater or less degree, of their

barbules, so that a part of the disc is surrounded by an almost

transparent zone, which gives to it a highly-finished aspect. But I have

elsewhere described[194] an exactly analogous variation in the hackles

of a sub-variety of the game-cock, in which the tips, having a metallic

lustre, "are separated from the lower part of the feather by a

symmetrically-shaped transparent zone, composed of the naked portions of

the barbs." The lower margin or base of the dark-blue centre of the

ocellus is deeply indented on the line of the shaft. The surrounding

zones likewise shew traces, as may be seen in the drawing (fig. 53), of

indentations, or rather breaks. These indentations are common to the

Indian and Javan peacocks (_Pavo cristatus_ and _P. muticus_); and they

seemed to me to deserve particular attention, as probably connected with

the development of the ocellus; but for a long time I could not

conjecture their meaning.

If we admit the principle of gradual evolution, there must formerly have

existed many species which presented every successive step between the

wonderfully elongated tail-coverts of the peacock and the short tail

coverts of all ordinary birds; and again between the magnificent ocelli

of the former, and the simpler ocelli or mere coloured spots of other

birds; and so with all the other characters of the peacock. Let us look

to the allied Gallinaceae for any still-existing gradations. The species

and sub-species of Polyplectron inhabit countries adjacent to the native

land of the peacock; and they so far resemble this bird that they are

sometimes called peacock-pheasants. I am also informed by Mr. Bartlett

that they resemble the peacock in their voice and in some of their

habits. During the spring the males, as previously described, strut

about before the comparatively plain-coloured females, expanding and

erecting their tail and wing-feathers, which are ornamented with

numerous ocelli. I request the reader to turn back to the drawing (fig.

51, p. 90) of a Polyplectron. In _P. Napoleonis_ the ocelli are confined

to the tail, and the back is of a rich metallic blue, in which respects

this species approaches the Java peacock. _P. Hardwickii_ possesses a

peculiar top-knot, somewhat like that of this same kind of peacock. The

ocelli on the wings and tail of the several species of Polyplectron are

either circular or oval, and consist of a beautiful, iridescent,

greenish-blue or greenish-purple disc, with a black border. This border

in _P. chinquis_ shades into brown which is edged with cream-colour, so

that the ocellus is here surrounded with differently, though not

brightly, shaded concentric zones. The unusual length of the

tail-coverts is another highly remarkable character in Polyplectron; for

in some of the species they are half as long, and in others two-thirds

of the length of the true tail-feathers. The tail-coverts are ocellated,

as in the peacock. Thus the several species of Polyplectron manifestly

make a graduated approach in the length of their tail-coverts, in the

zoning of the ocelli, and in some other characters, to the peacock.

[Illustration: Fig. 53. Feather of Peacock, about two-thirds of natural

size, carefully drawn by Mr. Ford. The transparent zone is represented

by the outermost white zone, confined to the upper end of the disc.]

Notwithstanding this approach, the first species of Polyplectron which I

happened to examine almost made me give up the search; for I found not

only that the true tail-feathers, which in the peacock are quite plain,

were ornamented with ocelli, but that the ocelli on all the feathers

differed fundamentally from those of the peacock, in there being two on

the same feather, (fig. 54), one on each side of the shaft. Hence I

concluded that the early progenitors of the peacock could not have

resembled in any degree a Polyplectron. But on continuing my search, I

observed that in some of the species the two ocelli stood very near each

other; that in the tail-feathers of _P. Hardwickii_ they touched each

other; and, finally, that in the tail-coverts of this same species as

well as of _P. malaccense_ (fig. 55) they were actually confluent. As

the central part alone is confluent, an indentation is left at both the

upper and lower ends; and the surrounding coloured zones are likewise

indented.

[Illustration: Fig. 54. Part of a tail-covert of Polyplectron chinquis,

with two oval ocelli of nat. size.]

[Illustration: Fig. 55. Part of a tail-covert of Polyplectron

malaccense, with the two oval ocelli, partially confluent, of nat.

size.]

A single ocellus is thus formed on each tail-covert, though still

plainly betraying its double origin. These confluent ocelli differ from

the single ocelli of the peacock in having an indentation at both ends,

instead of at the lower or basal end alone. The explanation, however, of

this difference is not difficult; in some species of Polyplectron the

two oval ocelli on the same feather stand parallel to each other; in

other species (as in _P. chinquis_) they converge towards one end; now

the partial confluence of two convergent ocelli would manifestly leave a

much deeper indentation at the divergent than at the convergent end. It

is also manifest that if the convergence were strongly pronounced and

the confluence complete, the indentation at the convergent end would

tend to be quite obliterated.

The tail-feathers in both species of peacock are entirely destitute of

ocelli, and this apparently is related to their being covered up and

concealed by the long tail-coverts. In this respect they differ

remarkably from the tail-feathers of Polyplectron, which in most of the

species are ornamented with larger ocelli than those on the

tail-coverts. Hence I was led carefully to examine the tail-feathers of

the several species of Polyplectron in order to discover whether the

ocelli in any of them shewed any tendency to disappear, and, to my great

satisfaction, I was successful. The central tail-feathers of _P.

Napoleonis_ have the two ocelli on each side of the shaft perfectly

developed; but the inner ocellus becomes less and less conspicuous on

the more exterior tail-feathers, until a mere shadow or rudimentary

vestige is left on the inner side of the outermost feather. Again, in

_P. malaccense_, the ocelli on the tail-coverts are, as we have seen,

confluent; and these feathers are of unusual length, being two-thirds of

the length of the tail-feathers, so that in both these respects they

resemble the tail-coverts of the peacock. Now in this species the two

central tail-feathers alone are ornamented, each with two

brightly-coloured ocelli, the ocelli having completely disappeared from

the inner sides of all the other tail-feathers. Consequently the

tail-coverts and tail-feathers of this species of Polyplectron make a

near approach in structure and ornamentation to the corresponding

feathers of the peacock.

As far, then, as the principle of gradation throws light on the steps by

which the magnificent train of the peacock has been acquired, hardly

anything more is needed. We may picture to ourselves a progenitor of

the peacock in an almost exactly intermediate condition between the

existing peacock, with his enormously elongated tail-coverts, ornamented

with single ocelli, and an ordinary gallinaceous bird with short

tail-coverts, merely spotted with some colour; and we shall then see in

our mind's eye, a bird possessing tail-coverts, capable of erection and

expansion, ornamented with two partially confluent ocelli, and long

enough almost to conceal the tail-feathers,--the latter having already

partially lost their ocelli; we shall see in short, a Polyplectron. The

indentation of the central disc and surrounding zones of the ocellus in

both species of peacock, seems to me to speak plainly in favour of this

view; and this structure is otherwise inexplicable. The males of

Polyplectron are no doubt very beautiful birds, but their beauty, when

viewed from a little distance, cannot be compared, as I formerly saw in

the Zoological Gardens, with that of the peacock. Many female

progenitors of the peacock must, during a long line of descent, have

appreciated this superiority; for they have unconsciously, by the

continued preference of the most beautiful males, rendered the peacock

the most splendid of living birds.

_Argus pheasant._--Another excellent case for investigation is offered

by the ocelli on the wing-feathers of the Argus pheasant, which are

shaded in so wonderful a manner as to resemble balls lying within

sockets, and which consequently differ from ordinary ocelli. No one, I

presume, will attribute the shading, which has excited the admiration of

many experienced artists, to chance--to the fortuitous concourse of

atoms of colouring matter. That these ornaments should have been formed

through the selection of many successive variations, not one of which

was originally intended to produce the ball-and-socket effect, seems as

incredible, as that one of Raphael's Madonnas should have been formed by

the selection of chance daubs of paint made by a long succession of

young artists, not one of whom intended at first to draw the human

figure. In order to discover how the ocelli have been developed, we

cannot look to a long line of progenitors, nor to various closely-allied

forms, for such do not now exist. But fortunately the several feathers

on the wing suffice to give us a clue to the problem, and they prove to

demonstration that a gradation is at least possible from a mere spot to

a finished ball-and-socket ocellus.

The wing-feathers, bearing the ocelli, are covered with dark stripes or

rows of dark spots, each stripe or row running obliquely down the outer

side of the shaft to an ocellus. The spots are generally elongated in a

transverse line to the row in which they stand. They often become

confluent, either in the line of the row--and then they form a

longitudinal stripe--or transversely, that is, with the spots in the

adjoining rows, and then they form transverse stripes. A spot sometimes

breaks up into smaller spots, which still stand in their proper places.

[Illustration: Fig. 56. Part of Secondary wing-feather of Argus

pheasant, shewing two, _a_ and _b_, perfect ocelli. A, B, C, &c., dark

stripes running obliquely down, each to an ocellus.

(Much of the web on both sides, especially to the left of the shaft, has

been cut off.)]

It will be convenient first to describe a perfect ball-and-socket

ocellus. This consists of an intensely black circular ring, surrounding

a space shaded so as exactly to resemble a ball. The figure here given

has been admirably drawn by Mr. Ford, and engraved, but a woodcut cannot

exhibit the exquisite shading of the original. The ring is almost always

slightly broken or interrupted (see fig. 56) at a point in the upper

half, a little to the right of and above the white shade on the enclosed

ball; it is also sometimes broken towards the base on the right hand.

These little breaks have an important meaning. The ring is always much

thickened, with the edges ill-defined towards the left-hand upper

corner the feather being held erect, in the position in which it is

here drawn. Beneath this thickened part there is on the surface of the

ball an oblique almost pure-white mark, which shades off downwards into

a pale-leaden hue, and this into yellowish and brown tints, which

insensibly become darker and darker towards the lower part of the ball.

It is this shading which gives so admirably the effect of light shining

on a convex surface. If one of the balls be examined, it will be seen

that the lower part is of a browner tint and is indistinctly separated

by a curved oblique line from the upper part, which is yellower and more

leaden; this oblique line runs at right angles to the longer axis of the

white patch of light, and indeed of all the shading; but this difference

in the tints, which cannot of course be shewn in the woodcut, does not

in the least interfere with the perfect shading of the ball.[195] It

should be particularly observed that each ocellus stands in obvious

connection with a dark stripe, or row of dark spots, for both occur

indifferently on the same feather. Thus in fig. 56 stripe A runs to

ocellus _a_; B runs to ocellus _b_; stripe C is broken in the upper

part, and runs down to the next succeeding ocellus, not represented in

the woodcut; D to the next lower one, and so with the stripes E and F.

Lastly, the several ocelli are separated from each other by a pale

surface bearing irregular black marks.

[Illustration: Fig. 57. Basal part of the Secondary wing-feather,

nearest to the body.]

I will next describe the other extreme of the series, namely the first

trace of an ocellus. The short secondary wing-feather (fig. 57), nearest

to the body, is marked like the other feathers, with oblique,

longitudinal, rather irregular, rows of spots. The lowest spot, or that

nearest the shaft, in the five lower rows (excluding the basal row) is a

little larger than the other spots in the same row, and a little more

elongated in a transverse direction. It differs also from the other

spots by being bordered on its upper side with some dull fulvous

shading. But this spot is not in any way more remarkable than those on

the plumage of many birds, and might easily be quite overlooked. The

next higher spot in each row does not differ at all from the upper ones

in the same row, although in the following series it becomes, as we

shall see, greatly modified. The larger spots occupy exactly the same

relative position on this feather as those occupied by the perfect

ocelli on the longer wing-feathers.

By looking to the next two or three succeeding secondary wing-feathers,

an absolutely insensible gradation can be traced from one of the

above-described lower spots, together with the next higher one in the

same row, to a curious ornament, which cannot be called an ocellus, and

which I will name, from the want of a better term, an "elliptic

ornament." These are shewn in the accompanying figure (fig. 58). We here

see several oblique rows, A, B, C, D (see the lettered diagram), &c., of

dark spots of the usual character. Each row of spots runs down to and is

connected with one of the elliptic ornaments, in exactly the same manner

as each stripe in fig. 56 runs down to, and is connected with, one of

the ball-and-socket ocelli. Looking to any one row, for instance, B, the

lowest spot or mark (_b_) is thicker and considerably longer than the

upper spots, and has its left extremity pointed and curved upwards. This

black mark is abruptly bordered on its upper side by a rather broad

space of richly-shaded tints, beginning with a narrow brown zone, which

passes into orange, and this into a pale leaden tint, with the end

towards the shaft much paler. This mark corresponds in every respect

with the larger, shaded spot, described in the last paragraph (fig. 57),

but is more highly developed and more brightly coloured. To the right

and above this spot (_b_), with its bright shading, there is a long,

narrow, black mark (_c_), belonging to the same row, and which is arched

a little downwards so as to face (_b_). It is also narrowly edged on the

lower side with a fulvous tint. To the left of and above _c_, in the

same oblique direction, but always more or less distinct from it, there

is another black mark (_d_). This mark is generally sub-triangular and

irregular in shape, but in the one lettered in the diagram is unusually

narrow, elongated, and regular. It apparently consists of a lateral and

broken prolongation of the mark (_c_), as I infer from traces of

similar prolongations from the succeeding upper spots; but I do not feel

sure of this. These three marks, _b_, _c_, and _d_, with the intervening

bright shades, form together the so-called elliptic ornament. These

ornaments stand in a line parallel to the shaft, and manifestly

correspond in position with the ball-and-socket ocelli. Their extremely

elegant appearance cannot be appreciated in the drawing, as the orange

and leaden tints, contrasting so well with the black marks, cannot be

shewn.

[Illustration: Fig. 58. Portion of one of the Secondary wing-feathers

near to the body; shewing the so-called elliptic ornaments. The

right-hand figure is given merely as a diagram for the sake of the

letters of reference.

A, B, C, &c. Rows of spots running down to and forming the elliptic

ornaments.

_b_. Lowest spot or mark in row B.

_c_. The next succeeding spot or mark in the same row.

_d_. Apparently a broken prolongation of the spot _c_ in the same

row B.]

Between one of the elliptic ornaments and a perfect ball-and-socket

ocellus, the gradation is so perfect that it is scarcely possible to

decide when the latter term ought to be used. I regret that I have not

given an additional drawing, besides fig. 58, which stands about

half-way in the series between one of the simple spots and a perfect

ocellus. The passage from the elliptic ornament into an ocellus is

effected by the elongation and greater curvature in opposed directions

of the lower black mark (_b_), and more especially of the upper one

(_c_), together with the contraction of the irregular sub-triangular or

narrow mark (_d_), so that at last these three marks become confluent,

forming an irregular elliptic ring. This ring is gradually rendered more

and more circular and regular, at the same time increasing in diameter.

Traces of the junction of all three elongated spots or marks, especially

of the two upper ones, can still be observed in many of the most perfect

ocelli. The broken state of the black ring on the upper side of the

ocellus in fig. 56 was pointed out. The irregular sub-triangular or

narrow mark (_d_) manifestly forms, by its contraction and equalisation,

the thickened portion of the ring on the left upper side of the perfect

ball-and-socket ocellus. The lower part of the ring is invariably a

little thicker than the other parts (see fig. 56), and this follows

from the lower black mark of the elliptic ornament (_b_) having been

originally thicker than the upper mark (_c_). Every step can be followed

in the process of confluence and modification; and the black ring which

surrounds the ball of the ocellus is unquestionably formed by the union

and modification of the three black marks, _b_, _c_, _d_, of the

elliptic ornament. The irregular zigzag black marks between the

successive ocelli (see again fig. 56) are plainly due to the breaking up

of the somewhat more regular but similar marks between the elliptic

ornaments.

The successive steps in the shading of the ball-and-socket ocelli can be

followed out with equal clearness. The brown, orange, and pale-leaden

narrow zones which border the lower black mark of the elliptic ornament

can be seen gradually to become more and more softened and shaded into

each other, with the upper lighter part towards the left-hand corner

rendered still lighter, so as to become almost white. But even in the

most perfect ball-and-socket ocelli a slight difference in the tints,

though not in the shading, between the upper and lower parts of the ball

can be perceived (as was before especially noticed), the line of

separation being oblique, in the same direction with the bright coloured

shades of the elliptic ornaments. Thus almost every minute detail in the

shape and colouring of the ball-and-socket ocelli can be shewn to follow

from gradual changes in the elliptic ornaments; and the development of

the latter can be traced by equally small steps from the union of two

almost simple spots, the lower one (fig. 57) having some dull fulvous

shading on the upper side.

[Illustration: Fig. 59. Portion near summit of one of the Secondary

wing-feathers, bearing perfect ball-and-socket ocelli.

_a._ Ornamented upper part.

_b._ Uppermost, imperfect ball-and-socket ocellus. (The

shading above the white mark on the summit of the ocellus is

here a little too dark.)

_c._ Perfect ocellus.]

The extremities of the longer secondary feathers which bear the perfect

ball-and-socket ocelli are peculiarly ornamented. (Fig. 59.) The oblique

longitudinal stripes suddenly cease upwards and become confused, and

above this limit the whole upper end of the feather (_a_) is covered

with white dots, surrounded by little black rings, standing on a dark

ground. Even the oblique stripe belonging to the uppermost ocellus (_b_)

is represented only by a very short irregular black mark with the usual,

curved, transverse base. As this stripe is thus abruptly cut off above,

we can understand, from what has gone before, how it is that the upper

thickened part of the ring is absent in the uppermost ocellus; for, as

before stated, this thickened part is apparently formed by a broken

prolongation of the next higher spot in the same row. From the absence

of the upper and thickened part of the ring, the uppermost ocellus,

though perfect in all other respects, appears as if its top had been

obliquely sliced off. It would, I think, perplex any one, who believes

that the plumage of the Argus pheasant was created as we now see it, to

account for the imperfect condition of the uppermost ocelli. I should

add that in the secondary wing-feather farthest from the body all the

ocelli are smaller and less perfect than on the other feathers, with

the upper parts of the external black rings deficient, as in the case

just mentioned. The imperfection here seems to be connected with the

fact that the spots on this feather shew less tendency than usual to

become confluent into stripes; on the contrary, they are often broken up

into smaller spots, so that two or three rows run down to each ocellus.

We have now seen that a perfect series can be followed, from two almost

simple spots, at first quite distinct from each other, to one of the

wonderful ball-and-socket ornaments. Mr. Gould, who kindly gave me some

of these feathers, fully agrees with me in the completeness of the

gradation. It is obvious that the stages in development exhibited by the

feathers on the same bird do not at all necessarily shew us the steps

which have been passed through by the extinct progenitors of the

species; but they probably give us the clue to the actual steps, and

they at least prove to demonstration that a gradation is possible.

Bearing in mind how carefully the male Argus pheasant displays his

plumes before the female, as well as the many facts rendering it

probable that female birds prefer the more attractive males, no one who

admits the agency of sexual selection, will deny that a simple dark spot

with some fulvous shading might be converted, through the approximation

and modification of the adjoining spots, together with some slight

increase of colour, into one of the so-called elliptic ornaments. These

latter ornaments have been shewn to many persons, and all have admitted

that they are extremely pretty, some thinking them even more beautiful

than the ball-and-socket ocelli. As the secondary plumes became

lengthened through sexual selection, and as the elliptic ornaments

increased in diameter, their colours apparently became less bright; and

then the ornamentation of the plumes had to be gained by improvements in

the pattern and shading; and this process has been carried on until the

wonderful ball-and-socket ocelli have been finally developed. Thus we

can understand--and in no other way as it seems to me--the present

condition and origin of the ornaments on the wing-feathers of the Argus

pheasant.

From the light reflected by the principle of gradation; from what we

know of the laws of variation; from the changes which have taken place

in many of our domesticated birds; and, lastly, from the character (as

we shall hereafter more clearly see) of the immature plumage of young

birds--we can sometimes indicate with a certain amount of confidence,

the probable steps by which the males have acquired their brilliant

plumage and various ornaments; yet in many cases we are involved in

darkness. Mr. Gould several years ago pointed out to me a humming-bird,

the _Urosticte benjamini_, remarkable from the curious differences

presented by the two sexes. The male, besides a splendid gorget, has

greenish-black tail-feathers, with the four _central_ ones tipped with

white; in the female, as with most of the allied species, the three

_outer_ tail-feathers on each side are tipped with white, so that the

male has the four central, whilst the female has the six exterior

feathers ornamented with white tips. What makes the case curious is

that, although the colouring of the tail differs remarkably in both

sexes of many kinds of humming-birds, Mr. Gould does not know a single

species, besides the Urosticte, in which the male has the four central

feathers tipped with white.

The Duke of Argyll, in commenting on this case,[196] passes over sexual

selection, and asks, "What explanation does the law of natural selection

give of such specific varieties as these?" He answers "none whatever;"

and I quite agree with him. But can this be so confidently said of

sexual selection? Seeing in how many ways the tail-feathers of

humming-birds differ, why should not the four central feathers have

varied in this one species alone, so as to have acquired white tips? The

variations may have been gradual, or somewhat abrupt as in the case

recently given of the humming-birds near Bogota, in which certain

individuals alone have the "central tail-feathers tipped with beautiful

green." In the female of the Urosticte I noticed extremely minute or

rudimental white tips to the two outer of the four central black

tail-feathers; so that here we have an indication of change of some kind

in the plumage of this species. If we grant the possibility of the

central tail-feathers of the male varying in whiteness, there is nothing

strange in such variations having been sexually selected. The white

tips, together with the small white ear-tufts, certainly add, as the

Duke of Argyll admits, to the beauty of the male; and whiteness is

apparently appreciated by other birds, as may be inferred from such

cases as the snow-white male of the Bell-bird. The statement made by Sir

E. Heron should not be forgotten, namely that his peahens, when debarred

from access to the pied peacock, would not unite with any other male,

and during that season produced no offspring. Nor is it strange that

variations in the tail-feathers of the Urosticte should have been

specially selected for the sake of ornament, for the next succeeding

genus in the family takes its name of Metallura from the splendour of

these feathers. Mr. Gould, after describing the peculiar plumage of the

Urosticte, adds, "that ornament and variety is the sole object, I have

myself but little doubt."[197] If this be admitted, we can perceive that

the males which were decked in the most elegant and novel manner would

have gained an advantage, not in the ordinary struggle for life, but in

rivalry with other males, and would consequently have left a larger

number of offspring to inherit their newly-acquired beauty.

CHAPTER XV.

BIRDS--_continued_.

Discussion why the males alone of some species, and both sexes

of other species, are brightly coloured--On sexually-limited

inheritance, as applied to various structures and to

brightly-coloured plumage--Nidification in relation to

colour--Loss of nuptial plumage during the winter.

We have in this chapter to consider, why with many kinds of birds the

female has not received the same ornaments as the male; and why with

many others, both sexes are equally, or almost equally, ornamented? In

the following chapter we shall consider why in some few rare cases the

female is more conspicuously coloured than the male.

In my 'Origin of Species'[198] I briefly suggested that the long tail of

the peacock would be inconvenient, and the conspicuous black colour of

the male capercailzie dangerous, to the female during the period of

incubation; and consequently that the transmission of these characters

from the male to the female offspring had been checked through natural

selection. I still think that this may have occurred in some few

instances: but after mature reflection on all the facts which I have

been able to collect, I am now inclined to believe that when the sexes

differ, the successive variations have generally been from the first

limited in their transmission to the same sex in which they first

appeared. Since my remarks appeared, the subject of sexual coloration

has been discussed in some very interesting papers by Mr. Wallace,[199]

who believes that in almost all cases the successive variations tended

at first to be transmitted equally to both sexes; but that the female

was saved, through natural selection, from acquiring the conspicuous

colours of the male, owing to the danger which she would thus have

incurred during incubation.

This view necessitates a tedious discussion on a difficult point, namely

whether the transmission of a character, which is at first inherited by

both sexes, can be subsequently limited in its transmission, by means of

selection, to one sex alone. We must bear in mind, as shewn in the

preliminary chapter on sexual selection, that characters which are

limited in their development to one sex are always latent in the other.

An imaginary illustration will best aid us in seeing the difficulty of

the case: we may suppose that a fancier wished to make a breed of

pigeons, in which the males alone should be coloured of a pale blue,

whilst the females retained their former slaty tint. As with pigeons

characters of all kinds are usually transmitted to both sexes equally,

the fancier would have to try to convert this latter form of inheritance

into sexually-limited transmission. All that he could do would be to

persevere in selecting every male pigeon which was in the least degree

of a paler blue; and the natural result of this process, if steadily

carried on for a long time, and if the pale variations were strongly

inherited or often recurred, would be to make his whole stock of a

lighter blue. But our fancier would be compelled to match, generation

after generation, his pale blue males with slaty females, for he wishes

to keep the latter of this colour. The result would generally be the

production either of a mongrel piebald lot, or more probably the speedy

and complete loss of the pale-blue colour, for the primordial slaty tint

would be transmitted with prepotent force. Supposing, however, that some

pale-blue males and slaty females were produced during each successive

generation, and were always crossed together; then the slaty females

would have, if I may use the expression, much blue blood in their veins,

for their fathers, grandfathers, etc., will all have been blue birds.

Under these circumstances it is conceivable (though I know of no

distinct facts rendering it probable) that the slaty females might

acquire so strong a latent tendency to pale-blueness, that they would

not destroy this colour in their male offspring, their female offspring

still inheriting the slaty tint. If so, the desired end of making a

breed with the two sexes permanently different in colour might be

gained.

The extreme importance, or rather necessity, of the desired character in

the above case, namely, pale-blueness, being present though in a latent

state in the female, so that the male offspring should not be

deteriorated, will be best appreciated as follows: the male of

Soemmerring's pheasant has a tail thirty-seven inches in length,

whilst that of the female is only eight inches; the tail of the male

common pheasant is about twenty inches, and that of the female twelve

inches long. Now if the female Soemmerring pheasant with her _short_

tail were crossed with the male common pheasant, there can be no doubt

that the male hybrid offspring would have a much _longer_ tail than that

of the pure offspring of the common pheasant. On the other hand, if the

female common pheasant, with her tail nearly _twice as long_ as that of

the female Soemmerring pheasant, were crossed with the male of the

latter, the male hybrid offspring would have a much _shorter_ tail than

that of the pure offspring of Soemmerring's pheasant.[200]

Our fancier, in order to make his new breed with the males of a decided

pale-blue tint, and the females unchanged, would have to continue

selecting the males during many generations; and each stage of paleness

would have to be fixed in the males, and rendered latent in the females.

The task would be an extremely difficult one, and has never been tried,

but might possibly succeed. The chief obstacle would be the early and

complete loss of the pale-blue tint, from the necessity of reiterated

crosses with the slaty female, the latter not having at first any

_latent_ tendency to produce pale-blue offspring.

On the other hand, if one or two males were to vary ever so slightly in

paleness, and the variations were from the first limited in their

transmission to the male sex, the task of making a new breed of the

desired kind would be easy, for such males would simply have to be

selected and matched with ordinary females. An analogous case has

actually occurred, for there are breeds of the pigeon in Belgium[201] in

which the males alone are marked with black striae. In the case of the

fowl, variations of colour limited in their transmission to the male sex

habitually occur. Even when this form of inheritance prevails, it might

well happen that some of the successive steps in the process of

variation might be transferred to the female, who would then come to

resemble in a slight degree the male, as occurs in some breeds of the

fowl. Or again, the greater number, but not all, of the successive

steps might be transferred to both sexes, and the female would then

closely resemble the male. There can hardly be a doubt that this is the

cause of the male pouter pigeon having a somewhat larger crop, and of

the male carrier pigeon having somewhat larger wattles, than their

respective females; for fanciers have not selected one sex more than the

other, and have had no wish that these characters should be more

strongly displayed in the male than in the female, yet this is the case

with both breeds.

The same process would have to be followed, and the same difficulties

would be encountered, if it were desired to make a breed with the

females alone of some new colour.

Lastly, our fancier might wish to make a breed with the two sexes

differing from each other, and both from the parent-species. Here the

difficulty would be extreme, unless the successive variations were from

the first sexually limited on both sides, and then there would be no

difficulty. We see this with the fowl; thus the two sexes of the

pencilled Hamburghs differ greatly from each other, and from the two

sexes of the aboriginal _Gallus bankiva_; and both are now kept constant

to their standard of excellence by continued selection, which would be

impossible unless the distinctive characters of both were limited in

their transmission. The Spanish fowl offers a more curious case; the

male has an immense comb, but some of the successive variations, by the

accumulation of which it was acquired, appear to have been transferred

to the female; for she has a comb many times larger than that of the

females of the parent-species. But the comb of the female differs in one

respect from that of the male, for it is apt to lop over; and within a

recent period it has been ordered by the fancy that this should always

be the case, and success has quickly followed the order. Now the

lopping of the comb must be sexually limited in its transmission,

otherwise it would prevent the comb of the male from being perfectly

upright, which would be abhorrent to every fancier. On the other hand

the uprightness of the comb in the male must likewise be a

sexually-limited character, otherwise it would prevent the comb of the

female from lopping over.

From the foregoing illustrations, we see that even with almost unlimited

time at command, it would be an extremely difficult and complex process,

though perhaps not impossible, to change through selection one form of

transmission into the other. Therefore, without distinct evidence in

each case, I am unwilling to admit that this has often been effected

with natural species. On the other hand by means of successive

variations, which were from the first sexually limited in their

transmission, there would not be the least difficulty in rendering a

male bird widely different in colour or in any other character from the

female; the latter being left unaltered, or slightly altered, or

specially modified for the sake of protection.

As bright colours are of service to the males in their rivalry with

other males, such colours would be selected, whether or not they were

transmitted exclusively to the same sex. Consequently the females might

be expected often to partake of the brightness of the males to a greater

or less degree; and this occurs with a host of species. If all the

successive variations were transmitted equally to both sexes, the

females would be undistinguishable from the males; and this likewise

occurs with many birds. If, however, dull colours were of high

importance for the safety of the female during incubation, as with many

ground birds, the females which varied in brightness, or which received

through inheritance from the males any marked accession of brightness,

would sooner or later be destroyed. But the tendency in the males to

continue for an indefinite period transmitting to their female offspring

their own brightness, would have to be eliminated by a change in the

form of inheritance; and this, as shewn by our previous illustration,

would be extremely difficult. The more probable result of the

long-continued destruction of the more brightly-coloured females,

supposing the equal form of transmission to prevail, would be the

lessening or annihilation of the bright colours of the males, owing to

their continually crossing with the duller females. It would be tedious

to follow out all the other possible results; but I may remind the

reader, as shewn in the eighth chapter, that if sexually-limited

variations in brightness occurred in the females, even if they were not

in the least injurious to them and consequently were not eliminated, yet

they would not be favoured or selected, for the male usually accepts any

female, and does not select the more attractive individuals;

consequently these variations would be liable to be lost, and would have

little influence on the character of the race; and this will aid in

accounting for the females being commonly less brightly-coloured than

the males.

In the chapter just referred to, instances were given, and any number

might have been added, of variations occurring at different ages, and

inherited at the same age. It was also shewn that variations which occur

late in life are commonly transmitted to the same sex in which they

first appeared; whilst variations occurring early in life are apt to be

transmitted to both sexes; not that all the cases of sexually-limited

transmission can thus be accounted for. It was further shewn that if a

male bird varied by becoming brighter whilst young, such variations

would be of no service until the age for reproduction had arrived, and

there was competition between rival males. If we suppose that

three-fourths of the young males of any species are on an average

destroyed by various enemies; then the chances would be as three to one

against any one individual more brightly-coloured than usual surviving

to propagate its kind. But in the case of birds which live on the ground

and which commonly need the protection of dull colours, bright tints

would be far more dangerous to the young and inexperienced than to the

adult males. Consequently the males which varied in brightness whilst

young would suffer much destruction and be eliminated through natural

selection; on the other hand the males which varied in this manner when

nearly mature, notwithstanding that they were exposed to some additional

danger, might survive, and from being favoured through sexual selection,

would procreate their kind. The brightly-coloured young males being

destroyed and the mature ones being successful in their courtship, may

account, on the principle of a relation existing between the period of

variation and the form of transmission, for the males alone of many

birds, having acquired and transmitted brilliant colours to their male

offspring alone. But I by no means wish to maintain that the influence

of age on the form of transmission is indirectly the sole cause of the

great difference in brilliancy between the sexes of many birds.

As with all birds in which the sexes differ in colour, it is an

interesting question whether the males alone have been modified through

sexual selection, the females being left, as far as this agency is

concerned, unchanged or only partially changed; or whether the females

have been specially modified through natural selection for the sake of

protection, I will discuss this question at considerable length, even

at greater length than its intrinsic importance deserves; for various

curious collateral points may thus be conveniently considered.

Before we enter on the subject of colour, more especially in reference

to Mr. Wallace's conclusions, it may be useful to discuss under a

similar point of view some other differences between the sexes. A breed

of fowls formerly existed in Germany[202] in which the hens were

furnished with spurs; they were good layers, but they so greatly

disturbed their nests with their spurs that they could not be allowed to

sit on their own eggs. Hence at one time it appeared to me probable that

with the females of the wild Gallinaceae the development of spurs had

been checked through natural selection, from the injury thus caused to

their nests. This seemed all the more probable as the wing-spurs, which

could not be injurious during nidification, are often as well developed

in the female as in the male; though in not a few cases they are rather

larger in the male. When the male is furnished with leg-spurs the female

almost always exhibits rudiments of them,--the rudiment sometimes

consisting of a mere scale, as with the species of Gallus. Hence it

might be argued that the females had aboriginally been furnished with

well-developed spurs, but that these had subsequently been lost either

through disuse or natural selection. But if this view be admitted, it

would have to be extended to innumerable other cases; and it implies

that the female progenitors of the existing spur-bearing species were

once encumbered with an injurious appendage.

In some few genera and species, as in Galloperdix, Acomus, and the Javan

peacock (_Pavo muticus_), the females, as well as the males, possess

well-developed spurs. Are we to infer from this fact that they construct

a different sort of nest, not liable to be injured by their spurs, from

that made by their nearest allies, so that there has been no need for

the removal of their spurs? Or are we to suppose that these females

especially require spurs for their defence? It is a more probable

conclusion that both the presence and absence of spurs in the females

result from different laws of inheritance having prevailed,

independently of natural selection. With the many females in which spurs

appear as rudiments, we may conclude that some few of the successive

variations, through which they were developed in the males, occurred

very early in life, and were as a consequence transferred to the

females. In the other and much rarer cases, in which the females possess

fully developed spurs, we may conclude that all the successive

variations were transferred to them; and that they gradually acquired

the inherited habit of not disturbing their nests.

The vocal organs and the variously-modified feathers for producing

sound, as well as the proper instincts for using them, often differ in

the two sexes, but are sometimes the same in both. Can such differences

be accounted for by the males having acquired these organs and

instincts, whilst the females have been saved from inheriting them, on

account of the danger to which they would have been exposed by

attracting the attention of birds or beasts of prey? This does not seem

to me probable, when we think of the multitude of birds which with

impunity gladden the country with their voices during the spring.[203]

It is a safer conclusion that as vocal and instrumental organs are of

special service only to the males during their courtship, these organs

were developed through sexual selection and continued use in this sex

alone--the successive variations and the effects of use having been from

the first limited in their transmission in a greater or less degree to

the male offspring.''

Many analogous cases could be advanced; for instance the plumes on the

head, which are generally longer in the male than in the female,

sometimes of equal length in both sexes, and occasionally absent in the

female,--these several cases sometimes occurring in the same group of

birds. It would be difficult to account for a difference of this kind

between the sexes on the principle of the female having been benefited

by possessing a slightly shorter crest than the male, and its consequent

diminution or complete suppression through natural selection. But I will

take a more favourable case, namely, the length of the tail. The long

train of the peacock would have been not only inconvenient but dangerous

to the peahen during the period of incubation and whilst accompanying

her young. Hence there is not the least _a priori_ improbability in the

development of her tail having been checked through natural selection.

But the females of various pheasants, which apparently are exposed on

their open nests to as much danger as the peahen, have tails of

considerable length. The females as well as the males of the _Menura

superba_ have long tails, and they build a domed nest, which is a great

anomaly in so large a bird. Naturalists have wondered how the female

Menura could manage her tail during incubation; but it is now

known[204] that she "enters the nest head first, and then turns round

with her tail sometimes over her back, but more often bent round by her

side. Thus in time the tail becomes quite askew, and is a tolerable

guide to the length of time the bird has been sitting." Both sexes of an

Australian kingfisher (_Tanysiptera sylvia_) have the middle

tail-feathers greatly lengthened; and as the female makes her nest in a

hole, these feathers become, as I am informed by Mr. R. B. Sharpe, much

crumpled during nidification.

In these two cases the great length of the tail-feathers must be in some

degree inconvenient to the female; and as in both species the

tail-feathers of the female are somewhat shorter than those of the male,

it might be argued that their full development had been prevented

through natural selection. Judging from these cases, if with the peahen,

the development of the tail had been checked only when it became

inconveniently or dangerously long, she would have acquired a much

longer tail than she actually possesses; for her tail is not nearly so

long, relatively to the size of her body, as that of many female

pheasants, nor longer than that of the female turkey. It must also be

borne in mind, that in accordance with this view as soon as the tail of

the peahen became dangerously long, and its development was consequently

checked, she would have continually reacted on her male progeny, and

thus have prevented the peacock from acquiring his present magnificent

train. We may therefore infer that the length of the tail in the peacock

and its shortness in the peahen are the result of the requisite

variations in the male having been from the first transmitted to the

male offspring alone.

We are led to a nearly similar conclusion with respect to the length of

the tail in the various species of pheasants. In the Eared pheasant

(_Crossoptilon auritum_) the tail is of equal length in both sexes,

namely, sixteen or seventeen inches; in the common pheasant it is about

twenty inches long in the male, and twelve in the female; in

Soemmerring's pheasant, thirty-seven inches in the male, and only

eight in the female; and lastly in Reeve's pheasant it is sometimes

actually seventy-two inches long in the male and sixteen in the female.

Thus in the several species, the tail of the female differs much in

length, irrespectively of that of the male; and this can be accounted

for as it seems to me, with much more probability, by the laws of

inheritance,--that is by the successive variations having been from the

first more or less closely limited in their transmission to the male

sex,--than by the agency of natural selection, owing to the length of

tail having been injurious in a greater or less degree to the females of

the several species.

We may now consider Mr. Wallace's arguments, in regard to the sexual

coloration of birds. He believes that the bright tints originally

acquired through sexual selection by the males, would in all or almost

all cases have been transmitted to the females, unless the transference

had been checked through natural selection. I may here remind the reader

that various facts bearing on this view have already been given under

reptiles, amphibians, fishes, and lepidoptera. Mr. Wallace rests his

belief chiefly, but not exclusively, as we shall see in the next

chapter, on the following statement,[205] that when both sexes are

coloured in a strikingly-conspicuous manner the nest is of such a

nature as to conceal the sitting bird; but when there is a marked

contrast of colour between the sexes, the male being gay and the female

dull-coloured, the nest is open and exposes the sitting bird to view.

This coincidence, as far as it goes, certainly supports the belief that

the females which sit on open nests have been specially modified for the

sake of protection. Mr. Wallace admits that there are, as might have

been expected, some exceptions to his two rules, but it is a question

whether the exceptions are not so numerous as seriously to invalidate

them.

There is in the first place much truth in the Duke of Argyll's

remark[206] that a large domed nest is more conspicuous to an enemy,

especially to all tree-haunting carnivorous animals, than a smaller open

nest. Nor must we forget that with many birds which build open nests the

males sit on the eggs and aid in feeding the young as well as the

females: this is the case, for instance, with _Pyranga aestiva_,[207] one

of the most splendid birds in the United States, the male being

vermilion, and the female light brownish-green. Now if brilliant colours

had been extremely dangerous to birds whilst sitting on their open

nests, the males in these cases would have suffered greatly. It might,

however, be of such paramount importance to the male to be brilliantly

coloured, in order to beat his rivals, that this would more than

compensate for some additional danger.

Mr. Wallace admits that with the King-crows (Dicrurus), Orioles, and

Pittidae, the females are conspicuously coloured, yet they build open

nests; but he urges that the birds of the first group are highly

pugnacious and could defend themselves; that those of the second group

take extreme care in concealing their open nests, but this does not

invariably hold good;[208] and that with the birds of the third group

the females are brightly coloured chiefly on the under surface. Besides

these cases the whole great family of pigeons, which are sometimes

brightly, and almost always conspicuously coloured, and which are

notoriously liable to the attacks of birds of prey, offers a serious

exception to the rule, for pigeons almost always build open and exposed

nests. In another large family, that of the Humming-birds, all the

species build open nests, yet with some of the most gorgeous species the

sexes are alike; and in the majority, the females, though less brilliant

than the males, are very brightly coloured. Nor can it be maintained

that all female humming-birds, which are brightly coloured, escape

detection by their tints being green, for some display on their upper

surfaces red, blue, and other colours.[209]

In regard to birds which build in holes or construct domed nests, other

advantages, as Mr. Wallace remarks, besides concealment are gained, such

as shelter from the rain, greater warmth, and in hot countries

protection from the rays of the sun;[210] so that it is no valid

objection to his view that many birds having both sexes obscurely

coloured build concealed nests.[211] The female Hornbills (_Buceros_),

for instance, of India and Africa are protected, during nidification,

with extraordinary care, for the male plaisters up the hole in which the

female sits on her eggs, and leaves only a small orifice through which

he feeds her; she is thus kept a close prisoner during the whole period

of incubation;[212] yet female hornbills are not more conspicuously

coloured than many other birds of equal size which build open nests. It

is a more serious objection to Mr. Wallace's view, as is admitted by

him, that in some few groups the males are brilliantly coloured and the

females obscure, and yet the latter hatch their eggs in domed nests.

This is the case with the Grallinae of Australia, the Superb Warblers

(Maluridae) of the same country, the Sun-birds (Nectariniae), and with

several of the Australian Honey-suckers or Meliphagidae.[213]

If we look to the birds of England we shall see that there is no close

and general relation between the colours of the female and the nature of

the nest constructed by her. About forty of our British birds (excluding

those of large size which could defend themselves) build in holes in

banks, rocks, or trees, or construct domed nests. If we take the colours

of the female goldfinch, bullfinch, or blackbird, as a standard of the

degree of conspicuousness, which is not highly dangerous to the sitting

female, then out of the above forty birds, the females of only twelve

can be considered as conspicuous to a dangerous degree, the remaining

twenty-eight being inconspicuous.[214] Nor is there any close relation

between a well-pronounced difference in colour between the two sexes,

and the nature of the nest constructed. Thus the male house-sparrow

(_Passer domesticus_) differs much from the female, the male

tree-sparrow (_P. montanus_) differs hardly at all, and yet both build

well-concealed nests. The two sexes of the common fly-catcher

(_Muscicapa grisola_) can hardly be distinguished, whilst the sexes of

the pied fly-catcher (_M. luctuosa_) differ considerably, and both build

in holes. The female blackbird (_Turdus merula_) differs much, the

female ring-ouzel (_T. torquatus_) differs less, and the female common

thrush (_T. musicus_) hardly at all from their respective males; yet all

build open nests. On the other hand, the not very distantly-allied

water-ouzel (_Cinclus aquaticus_) builds a domed nest, and the sexes

differ about as much as in the case of the ring-ouzel. The black and red

grouse (_Tetrao tetrix_ and _T. Scoticus_) build open nests, in equally

well-concealed spots, but in the one species the sexes differ greatly,

and in the other very little.

Notwithstanding the foregoing objections, I cannot doubt, after reading

Mr. Wallace's excellent essay, that looking to the birds of the world,

a large majority of the species in which the females are conspicuously

coloured (and in this case the males with rare exceptions are equally

conspicuous), build concealed nests for the sake of protection. Mr.

Wallace enumerates[215] a long series of groups in which this rule holds

good; but it will suffice here to give, as instances, the more familiar

groups of kingfishers, toucans, trogons, puff-birds (Capitonidae),

plaintain-eaters (Musophagae), woodpeckers, and parrots. Mr. Wallace

believes that in these groups, as the males gradually acquired through

sexual selection their brilliant colours, these were transferred to the

females and were not eliminated by natural selection, owing to the

protection which they already enjoyed from their manner of nidification.

According to this view, their present manner of nesting was acquired

before their present colours. But it seems to me much more probable that

in most cases as the females were gradually rendered more and more

brilliant from partaking of the colours of the male, they were gradually

led to change their instincts (supposing that they originally built open

nests), and to seek protection by building domed or concealed nests. No

one who studies, for instance, Audubon's account of the differences in

the nests of the same species in the Northern and Southern United

States,[216] will feel any great difficulty in admitting that birds,

either by a change (in the strict sense of the word) of their habits, or

through the natural selection of so-called spontaneous variations of

instinct, might readily be led to modify their manner of nesting.

This way of viewing the relation, as far as it holds good, between the

bright colours of female birds and their manner of nesting, receives

some support from certain analogous cases occurring in the Sahara

Desert. Here, as in most other deserts, various birds, and many other

animals, have had their colours adapted in a wonderful manner to the

tints of the surrounding surface. Nevertheless there are, as I am

informed by the Rev. Mr. Tristram, some curious exceptions to the rule;

thus the male of the _Monticola cyanea_ is conspicuous from his bright

blue colour, and the female almost equally conspicuous from her mottled

brown and white plumage; both sexes of two species of Dromolaea are of a

lustrous black; so that these three birds are far from receiving

protection from their colours, yet they are able to survive, for they

have acquired the habit, when in danger, of taking refuge in holes or

crevices in the rocks.

With respect to the above-specified groups of birds, in which the

females are conspicuously coloured and build concealed nests, it is not

necessary to suppose that each separate species had its nidifying

instinct specially modified; but only that the early progenitors of each

group were gradually led to build domed or concealed nests; and

afterwards transmitted this instinct, together with their bright

colours, to their modified descendants. This conclusion, as far as it

can be trusted, is interesting, namely, that sexual selection, together

with equal or nearly equal inheritance by both sexes, have indirectly

determined the manner of nidification of whole groups of birds.

Even in the groups in which, according to Mr. Wallace, the females from

being protected during nidification, have not had their bright colours

eliminated through natural selection, the males often differ in a

slight, and occasionally in a considerable degree, from the females.

This is a significant fact, for such differences in colour must be

accounted for on the principle of some of the variations in the males

having been from the first limited in their transmission to the same

sex; as it can hardly be maintained that these differences, especially

when very slight, serve as a protection to the female. Thus all the

species in the splendid group of the Trogons build in holes; and Mr.

Gould gives figures[217] of both sexes of twenty-five species, in all of

which, with one partial exception, the sexes differ sometimes slightly,

sometimes conspicuously, in colour,--the males being always more

beautiful than the females, though the latter are likewise beautiful.

All the species of kingfisher build in holes, and with most of the

species the sexes are equally brilliant, and thus far Mr. Wallace's rule

holds good; but in some of the Australian species the colours of the

females are rather less vivid than those of the male; and in one

splendidly-coloured species, the sexes differ so much that they were at

first thought to be specifically distinct.[218] Mr. R. B. Sharpe, who

has especially studied this group, has shewn me some American species

(Ceryle) in which the breast of the male is belted with black. Again, in

Carcineutes, the difference between the sexes is conspicuous: in the

male the upper surface is dull-blue banded with black, the lower surface

being partly fawn-coloured, and there is much red about the head; in the

female the upper surface is reddish-brown banded with black, and the

lower surface white with black markings. It is an interesting fact, as

shewing how the same peculiar style of sexual colouring often

characterises allied forms, that in three species of Dacelo the male

differs from the female only in the tail being dull-blue banded with

black, whilst that of the female is brown with blackish bars; so that

here the tail differs in colour in the two sexes in exactly the same

manner as the whole upper surface in the sexes of Carcineutes.

With parrots, which likewise build in holes, we find analogous cases: in

most of the species both sexes are brilliantly coloured and

undistinguishable, but in not a few species the males are coloured

rather more vividly than the females, or even very differently from

them. Thus, besides other strongly-marked differences, the whole under

surface of the male King Lory (_Aprosmictus scapulatus_) is scarlet,

whilst the throat and chest of the female is green tinged with red: in

the _Euphema splendida_ there is a similar difference, the face and

wing-coverts moreover of the female being of a paler blue than in the

male.[219] In the family of the tits (_Parinae_), which build concealed

nests, the female of our common blue tomtit (_Parus caeruleus_) is "much

less brightly coloured" than the male; and in the magnificent Sultan

yellow tit of India the difference is greater.[220]

Again in the great group of the woodpeckers,[221] the sexes are

generally nearly alike, but in the _Megapicus validus_ all those parts

of the head, neck, and breast, which are crimson in the male are pale

brown in the female. As in several woodpeckers the head of the male is

bright crimson, whilst that of the female is plain, it occurred to me

that this colour might possibly make the female dangerously conspicuous,

whenever she put her head out of the hole containing her nest, and

consequently that this colour, in accordance with Mr. Wallace's belief,

had been eliminated. This view is strengthened by what Malherbe states

with respect to _Indopicus carlotta_; namely, that the young females,

like the young males, have some crimson about their heads, but that this

colour disappears in the adult female, whilst it is intensified in the

adult male. Nevertheless the following considerations render this view

extremely doubtful: the male takes a fair share in incubation,[222] and

would be thus far almost equally exposed to danger; both sexes of many

species have their heads of an equally bright crimson; in other species

the difference between the sexes in the amount of scarlet is so slight

that it can hardly make any appreciable difference in the danger

incurred; and lastly, the colouring of the head in the two sexes often

differs slightly in other ways.

The cases, as yet given, of slight and graduated differences in colour

between the males and females in the groups, in which as a general rule

the sexes resemble each other, all relate to species which build domed

or concealed nests. But similar gradations may likewise be observed in

groups in which the sexes as a general rule resemble each other, but

which build open nests. As I have before instanced the Australian

parrots, so I may here instance, without giving any details, the

Australian pigeons.[223] It deserves especial notice that in all these

cases the slight differences in plumage between the sexes are of the

same general nature as the occasionally greater differences. A good

illustration of this fact has already been afforded by those kingfishers

in which either the tail alone or the whole upper surface of the plumage

differs in the same manner in the two sexes. Similar cases may be

observed with parrots and pigeons. The differences in colour between the

sexes of the same species are, also, of the same general nature as the

differences in colour between the distinct species of the same group.

For when in a group in which the sexes are usually alike, the male

differs considerably from the female, he is not coloured in a quite new

style. Hence we may infer that within the same group the special colours

of both sexes when they are alike, and the colours of the male, when he

differs slightly or even considerably from the female, have in most

cases been determined by the same general cause; this being sexual

selection.

It is not probable, as has already been remarked, that differences in

colour between the sexes, when very slight, can be of service to the

female as a protection. Assuming, however, that they are of service,

they might be thought to be cases of transition; but we have no reason

to believe that many species at any one time are undergoing change.

Therefore we can hardly admit that the numerous females which differ

very slightly in colour from their males are now all commencing to

become obscure for the sake of protection. Even if we consider somewhat

more marked sexual differences, is it probable, for instance, that the

head of the female chaffinch, the crimson on the breast of the female

bullfinch,--the green of the female greenfinch,--the crest of the female

golden-crested wren, have all been rendered less bright by the slow

process of selection for the sake of protection? I cannot think so; and

still less with the slight differences between the sexes of those birds

which build concealed nests. On the other hand, the differences in

colour between the sexes, whether great or small, may to a large extent

be explained on the principle of the successive variations, acquired by

the males through sexual selection, having been from the first more or

less limited in their transmission to the females. That the degree of

limitation should differ in different species of the same group will not

surprise any one who has studied the laws of inheritance, for they are

so complex that they appear to us in our ignorance to be capricious in

their action.[224]

As far as I can discover there are very few groups of birds containing a

considerable number of species, in which all have both sexes brilliantly

coloured and alike; but this appears to be the case, as I hear from Mr.

Sclater, with the Musophagae or plaintain-eaters. Nor do I believe that

any large group exists in which the sexes of all the species are widely

dissimilar in colour: Mr. Wallace informs me that the chatterers of S.

America (_Cotingidae_) offer one of the best instances; but with some of

the species, in which the male has a splendid red breast, the female

exhibits some red on her breast; and the females of other species shew

traces of the green and other colours of the males. Nevertheless we have

a near approach to close sexual similarity or dissimilarity throughout

several groups: and this, from what has just been said of the

fluctuating nature of inheritance, is a somewhat surprising

circumstance. But that the same laws should largely prevail with allied

animals is not surprising. The domestic fowl has produced a great

number of breeds and sub-breeds, and in these the sexes generally differ

in plumage; so that it has been noticed as a remarkable circumstance

when in certain sub-breeds they resemble each other. On the other hand,

the domestic pigeon has likewise produced a vast number of distinct

breeds and sub-breeds, and in these, with rare exceptions, the two sexes

are identically alike. Therefore if other species of Gallus and Columba

were domesticated and varied, it would not be rash to predict that the

same general rules of sexual similarity and dissimilarity, depending on

the form of transmission, would, in both cases, hold good. In a similar

manner the same form of transmission has generally prevailed throughout

the same natural groups, although marked exceptions to this rule occur.

Within the same family or even genus, the sexes may be identically alike

or very different in colour. Instances have already been given relating

to the same genus, as with sparrows, fly-catchers, thrushes and grouse.

In the family of pheasants the males and females of almost all the

species are wonderfully dissimilar, but are quite similar in the eared

pheasant or _Crossoptilon auritum_. In two species of Chloephaga, a genus

of geese, the males cannot be distinguished from the females, except by

size; whilst in two others, the sexes are so unlike that they might

easily be mistaken for distinct species.[225]

The laws of inheritance can alone account for the following cases, in

which the female by acquiring at a late period of life certain

characters proper to the male, ultimately comes to resemble him in a

more or less complete manner. Here protection can hardly have come into

play. Mr. Blyth informs me that the females of _Oriolus melanocephalus_

and of some allied species, when sufficiently mature to breed, differ

considerably in plumage from the adult males; but after the second or

third moults they differ only in their beaks having a slight greenish

tinge. In the dwarf bitterns (Ardetta), according to the same authority,

"the male acquires his final livery at the first moult, the female not

before the third or fourth moult; in the meanwhile she presents an

intermediate garb, which is ultimately exchanged for the same livery as

that of the male." So again the female _Falco peregrinus_ acquires her

blue plumage more slowly than the male. Mr. Swinhoe states that with one

of the Drongo shrikes (_Dicrurus macrocercus_) the male whilst almost a

nestling, moults his soft brown plumage and becomes of a uniform glossy

greenish-black; but the female retains for a long time the white striae

and spots on the axillary feathers; and does not completely assume the

uniform black colour of the male for the first three years. The same

excellent observer remarks that in the spring of the second year the

female spoonbill (Platalea) of China resembles the male of the first

year, and that apparently it is not until the third spring that she

acquires the same adult plumage as that possessed by the male at a much

earlier age. The female _Bombycilla carolinensis_ differs very little

from the male, but the appendages, which like beads of red sealing-wax

ornament the wing-feathers, are not developed in her so early in life as

in the male. The upper mandible in the male of an Indian parrakeet

(_Palaeornis Javanicus_) is coral-red from his earliest youth, but in the

female, as Mr. Blyth has observed with caged and wild birds, it is at

first black and does not become red until the bird is at least a year

old, at which age the sexes resemble each other in all respects. Both

sexes of the wild turkey are ultimately furnished with a tuft of

bristles on the breast, but in two-year-old birds the tuft is about four

inches long in the male and hardly apparent in the female; when,

however, the latter has reached her fourth year, it is from four to five

inches in length.[226]

In these cases, the females follow a normal course of development in

ultimately becoming like the males; and such cases must not be

confounded with those in which diseased or old females assume masculine

characters, or with those in which perfectly fertile females, whilst

young, acquire through variation or some unknown cause the characters of

the male.[227] But all these cases have so much in common that they

depend, according to the hypothesis of pangenesis, on gemmules derived

from each part of the male being present, though latent, in the female;

their development following on some slight change in the elective

affinities of her constituent tissues.

A few words must be added on changes of plumage in relation to the

season of the year. From reasons formerly assigned there can be little

doubt that the elegant plumes, long pendant feathers, crests, &c., of

egrets, herons, and many other birds, which are developed and retained

only during the summer, serve exclusively for ornamental or nuptial

purposes, though common to both sexes. The female is thus rendered more

conspicuous during the period of incubation than during the winter; but

such birds as herons and egrets would be able to defend themselves. As,

however, plumes would probably be inconvenient and certainly of no use

during the winter, it is possible that the habit of moulting twice in

the year may have been gradually acquired through natural selection for

the sake of casting off inconvenient ornaments during the winter. But

this view cannot be extended to the many waders, in which the summer and

winter plumages differ very little in colour. With defenceless species,

in which either both sexes or the males alone become extremely

conspicuous during the breeding-season,--or when the males acquire at

this season such long wing or tail-feathers as to impede their flight,

as with Cosmetornis and Vidua,--it certainly at first appears highly

probable that the second moult has been gained for the special purpose

of throwing off these ornaments. We must, however, remember that many

birds, such as Birds of Paradise, the Argus pheasant and peacock, do not

cast their plumes during the winter; and it can hardly be maintained

that there is something in the constitution of these birds, at least of

the Gallinaceae, rendering a double moult impossible, for the ptarmigan

moults thrice in the year.[228] Hence it must be considered as doubtful

whether the many species which moult their ornamental plumes or lose

their bright colours during the winter, have acquired this habit on

account of the inconvenience or danger which they would otherwise have

suffered.

I conclude, therefore, that the habit of moulting twice in the year was

in most or all cases first acquired for some distinct purpose, perhaps

for gaining a warmer winter covering; and that variations in the plumage

occurring during the summer were accumulated through sexual selection,

and transmitted to the offspring at the same season of the year. Such

variations being inherited either by both sexes or by the males alone,

according to the form of inheritance which prevailed. This appears more

probable than that these species in all cases originally tended to

retain their ornamental plumage during the winter, but were saved from

this through natural selection, owing to the inconvenience or danger

thus caused.

I have endeavoured in this chapter to shew that the arguments are not

trustworthy in favour of the view that weapons, bright colours, and

various ornaments, are now confined to the males owing to the

conversion, by means of natural selection, of a tendency to the equal

transmission of characters to both sexes into transmission to the male

sex alone. It is also doubtful whether the colours of many female birds

are due to the preservation, for the sake of protection, of variations

which were from the first limited in their transmission to the female

sex. But it will be convenient to defer any further discussion on this

subject until I treat, in the following chapter, on the differences in

plumage between the young and old.

CHAPTER XVI.

Birds--_concluded_.

The immature plumage in relation to the character of the

plumage in both sexes when adult--Six classes of cases--Sexual

differences between the males of closely-allied or

representative species--The female assuming the characters of

the male--Plumage of the young in relation to the summer and

winter plumage of the adults--On the increase of beauty in the

Birds of the World--Protective

colouring--Conspicuously-coloured birds--Novelty

appreciated--Summary of the four chapters on Birds.

We must now consider the transmission of characters as limited by age in

reference to sexual selection. The truth and importance of the principle

of inheritance at corresponding ages need not here be discussed, as

enough has already been said on the subject. Before giving the several

rather complex rules or classes of cases, under which all the

differences in plumage between the young and the old, as far as known to

me, may be included, it will be well to make a few preliminary remarks.

With animals of all kinds when the young differ in colour from the

adults, and the colours of the former are not, as far as we can see, of

any special service, they may generally be attributed, like various

embryological structures, to the retention by the young of the character

of an early progenitor. But this view can be maintained with confidence,

only when the young of several species closely resemble each other, and

likewise resemble other adult species belonging to the same group; for

the latter are the living proofs that such a state of things was

formerly possible. Young lions and pumas are marked with feeble stripes

or rows of spots, and as many allied species both young and old are

similarly marked, no naturalist, who believes in the gradual evolution

of species, will doubt that the progenitor of the lion and puma was a

striped animal, the young having retained vestiges of the stripes, like

the kittens of black cats, which when grown up are not in the least

striped. Many species of deer, which when mature are not spotted, are

whilst young covered with white spots, as are likewise some few species

in their adult state. So again the young in the whole family of pigs

(Suidae), and in certain rather distantly-allied animals, such as the

tapir, are marked with dark longitudinal stripes; but here we have a

character apparently derived from an extinct progenitor, and now

preserved by the young alone. In all such cases the old have had their

colours changed in the course of time, whilst the young have remained

but little altered, and this has been effected through the principle of

inheritance at corresponding ages.

This same principle applies to many birds belonging to various groups,

in which the young closely resemble each other, and differ much from

their respective adult parents. The young of almost all the Gallinaceae,

and of some distantly-allied birds such as ostriches, are whilst covered

with down longitudinally striped; but this character points back to a

state of things so remote that it hardly concerns us. Young crossbills

(Loxia) have at first straight beaks like those of other finches, and in

their immature striated plumage they resemble the mature redpole and

female siskin, as well as the young of the goldfinch, greenfinch, and

some other allied species. The young of many kinds of buntings

(Emberiza) resemble each other, and likewise the adult state of the

common bunting, _E. miliaria_. In almost the whole large group of

thrushes the young have their breasts spotted--a character which is

retained by many species throughout life, but is quite lost by others,

as by the _Turdus migratorius_. So again with many thrushes, the

feathers on the back are mottled before they are moulted for the first

time, and this character is retained for life by certain eastern

species. The young of many species of shrikes (Lanius), of some

woodpeckers, and of an Indian pigeon (_Chalcophaps Indicus_), are

transversely striped on the under surface; and certain allied species or

genera when adult are similarly marked. In some closely-allied and

resplendent Indian cuckoos (Chrysococcyx), the species when mature

differ considerably from each other in colour, but the young cannot be

distinguished. The young of an Indian goose (_Sarkidiornis melanonotus_)

closely resemble in plumage an allied genus, Dendrocygna, when

mature.[229] Similar facts will hereafter be given in regard to certain

herons. Young black grouse (_Tetrao tetrix_) resemble the young as well

as the old of certain other species, for instance the red grouse or _T.

scoticus_. Finally, as Mr. Blyth, who has attended closely to this

subject, has well remarked, the natural affinities of many species are

best exhibited in their immature plumage; and as the true affinities of

all organic beings depend on their descent from a common progenitor,

this remark strongly confirms the belief that the immature plumage

approximately shews us the former or ancestral condition of the species.

Although many young birds belonging to various orders thus give us a

glimpse of the plumage of their remote progenitors, yet there are many

other birds, both dull-coloured and bright-coloured, in which the young

closely resemble their parents. With such species the young of the

different species cannot resemble each other more closely than do the

parents; nor can they present striking resemblances to allied forms in

their adult state. They give us but little insight into the plumage of

their progenitors, excepting in so far that when the young and the old

are coloured in the same general manner throughout a whole group of

species, it is probable that their progenitors were similarly coloured.

We may now consider the classes of cases or rules under which the

differences and resemblances, between the plumage of the young and the

old, of both sexes or of one sex alone, may be grouped. Rules of this

kind were first enounced by Cuvier; but with the progress of knowledge

they require some modification and amplification. This I have attempted

to do, as far as the extreme complexity of the subject permits, from

information derived from various sources; but a full essay on this

subject by some competent ornithologist is much needed. In order to

ascertain to what extent each rule prevails, I have tabulated the facts

given in four great works, namely, by Macgillivray on the birds of

Britain, Audubon on those of North America, Jerdon on those of India,

and Gould on those of Australia. I may here premise, firstly, that the

several cases or rules graduate into each other; and secondly, that when

the young are said to resemble their parents, it is not meant that they

are identically alike, for their colours are almost always rather less

vivid, and the feathers are softer and often of a different shape.

RULES OR CLASSES OF CASES.

I. When the adult male is more beautiful or conspicuous than the adult

female, the young of both sexes in their first plumage closely resemble

the adult female, as with the common fowl and peacock; or, as

occasionally occurs, they resemble her much more closely than they do

the adult male.

II. When the adult female is more conspicuous than the adult male, as

sometimes though rarely occurs, the young of both sexes in their first

plumage resemble the adult male.

III. When the adult male resembles the adult female, the young of both

sexes have a peculiar first plumage of their own, as with the robin.

IV. When the adult male resembles the adult female, the young of both

sexes in their first plumage resemble the adults, as with the

kingfisher, many parrots, crows, hedge-warblers.

V. When the adults of both sexes have a distinct winter and summer

plumage, whether or not the male differs from the female, the young

resemble the adults of both sexes in their winter dress, or much more

rarely in their summer dress, or they resemble the females alone; or the

young may have an intermediate character; or again they may differ

greatly from the adults in both their seasonal plumages.

VI. In some few cases the young in their first plumage differ from each

other according to sex; the young males resembling more or less closely

the adult males, and the young females more or less closely the adult

females.

CLASS I.--In this class, the young of both sexes resemble, more or less

closely, the adult female, whilst the adult male differs, often in the

most conspicuous manner, from the adult female. Innumerable instances

in all Orders could be given; it will suffice to call to mind the common

pheasant, duck, and house-sparrow. The cases under this class graduate

into others. Thus the two sexes when adult may differ so slightly, and

the young so slightly from the adults, that it is doubtful whether such

cases ought to come under the present, or under the third or fourth

classes. So again the young of both sexes, instead of being quite alike,

may differ in a slight degree from each other, as in our sixth class.

These transitional cases, however, are few in number, or at least are

not strongly pronounced, in comparison with those which come strictly

under the present class.

The force of the present law is well shewn in those groups, in which, as

a general rule, the two sexes and the young are all alike; for when the

male in these groups does differ from the female, as with certain

parrots, kingfishers, pigeons, &c., the young of both sexes resemble the

adult female.[230] We see the same fact exhibited still more clearly in

certain anomalous cases; thus the male of _Heliothrix auriculata_ (one

of the humming-birds) differs conspicuously from the female in having a

splendid gorget and fine ear-tufts, but the female is remarkable from

having a much longer tail than that of the male; now the young of both

sexes resemble (with the exception of the breast being spotted with

bronze) the adult female in all respects including the length of her

tail, so that the tail of the male actually becomes shorter as he

reaches maturity, which is a most unusual circumstance.[231] Again, the

plumage of the male goosander (_Mergus merganser_) is more conspicuously

coloured, with the scapular and secondary wing-feathers much longer than

in the female, but differently from what occurs, as far as I know, in

any other bird, the crest of the adult male, though broader than that of

the female, is considerably shorter, being only a little above an inch

in length; the crest of the female being two and a half inches long. Now

the young of both sexes resemble in all respects the adult female, so

that their crests are actually of greater length though narrower than in

the adult male.[232]

When the young and the females closely resemble each other and both

differ from the male, the most obvious conclusion is that the male alone

has been modified. Even in the anomalous cases of the Heliothrix and

Mergus, it is probable that originally both adult sexes were furnished,

the one species with a much elongated tail, and the other with a much

elongated crest, these characters having since been partially lost by

the adult males from some unexplained cause, and transmitted in their

diminished state to their male offspring alone, when arrived at the

corresponding age of maturity. The belief that in the present class the

male alone has been modified, as far as the differences between the male

and the female together with her young are concerned, is strongly

supported by some remarkable facts recorded by Mr. Blyth,[233] with

respect to closely-allied species which represent each other in distinct

countries. For with several of these representative species the adult

males have undergone a certain amount of change and can be

distinguished; the females and the young being undistinguishable, and

therefore absolutely unchanged. This is the case with certain Indian

chats (Thamnobia), with certain honey-suckers (Nectarinia), shrikes

(Tephrodornis), certain kingfishers (Tanysiptera), Kallij pheasants

(Gallophasis), and tree-partridges (Arboricola).

In some analogous cases, namely with birds having a distinct summer and

winter plumage, but with the two sexes nearly alike, certain

closely-allied species can easily be distinguished in their summer or

nuptial plumage, yet are undistinguishable in their winter as well as in

their immature plumage. This is the case with some of the closely-allied

Indian wagtails or Motacillae. Mr. Swinhoe[234] informs me that three

species of Ardeola, a genus of herons, which represent each other on

separate continents, are "most strikingly different" when ornamented

with their summer plumes, but are hardly, if at all, distinguishable

during the winter. The young also of these three species in their

immature plumage closely resemble the adults in their winter dress. This

case is all the more interesting because with two other species of

Ardeola both sexes retain, during the winter and summer, nearly the same

plumage as that possessed by the three first species during the winter

and in their immature state; and this plumage, which is common to

several distinct species at different ages and seasons, probably shews

us how the progenitor of the genus was coloured. In all these cases, the

nuptial plumage which we may assume was originally acquired by the adult

males during the breeding-season, and transmitted to the adults of both

sexes at the corresponding season, has been modified, whilst the winter

and immature plumages have been left unchanged.

The question naturally arises, how is it that in these latter cases the

winter plumage of both sexes, and in the former cases the plumage of the

adult females, as well as the immature plumage of the young, have not

been at all affected? The species which represent each other in distinct

countries will almost always have been exposed to somewhat different

conditions, but we can hardly attribute the modification of the plumage

in the males alone to this action, seeing that the females and the

young, though similarly exposed, have not been affected. Hardly any fact

in nature shews us more clearly how subordinate in importance is the

direct action of the conditions of life, in comparison with the

accumulation through selection of indefinite variations, than the

surprising difference between the sexes of many birds; for both sexes

must have consumed the same food and have been exposed to the same

climate. Nevertheless we are not precluded from believing that in the

course of time new conditions may produce some direct effect; we see

only that this is subordinate in importance to the accumulated results

of selection. When, however, a species migrates into a new country, and

this must precede the formation of representative species, the changed

conditions to which they will almost always have been exposed will

cause them to undergo, judging from a widely-spread analogy, a certain

amount of fluctuating variability. In this case sexual selection, which

depends on an element eminently liable to change--namely the taste or

admiration of the female--will have had new shades of colour or other

differences to act on and accumulate; and as sexual selection is always

at work, it would (judging from what we know of the results on domestic

animals of man's unintentional selection), be a surprising fact if

animals inhabiting separate districts, which can never cross and thus

blend their newly-acquired characters, were not, after a sufficient

lapse of time, differently modified. These remarks likewise apply to the

nuptial or summer plumage, whether confined to the males or common to

both sexes.

Although the females of the above closely-allied species, together with

their young, differ hardly at all from each other, so that the males

alone can be distinguished, yet in most cases the females of the species

within the same genus obviously differ from each other. The differences,

however, are rarely as great as between the males. We see this clearly

in the whole family of the Gallinaceae: the females, for instance, of the

common and Japan pheasant, and especially of the gold and Amherst

pheasant--of the silver pheasant and the wild fowl--resemble each other

very closely in colour, whilst the males differ to an extraordinary

degree. So it is with the females of most of the Cotingidae, Fringillidae,

and many other families. There can indeed be no doubt that, as a general

rule, the females have been modified to a less extent than the males.

Some few birds, however, offer a singular and inexplicable exception;

thus the females of _Paradisea apoda_ and _P. papuana_ differ from each

other more than do their respective males;[235] the female of the

latter species having the under surface pure white, whilst the female

_P. apoda_ is deep brown beneath. So, again, as I hear from Professor

Newton, the males of two species of Oxynotus (shrikes), which represent

each other in the islands of Mauritius and Bourbon,[236] differ but

little in colour, whilst the females differ much. In the Bourbon species

the female appears to have partially retained an immature condition of

plumage, for at first sight she "might be taken for the young of the

Mauritian species." These differences may be compared with those which

occur, independently of selection by man, and which we cannot explain,

in certain sub-breeds of the game-fowl, in which the females are very

different, whilst the males can hardly be distinguished.[237]

As I account so largely by sexual selection for the differences between

the males of allied species, how can the differences between the females

be accounted for in all ordinary cases? We need not here consider the

species which belong to distinct genera; for with these, adaptation to

different habits of life, and other agencies, will have come into play.

In regard to the differences between the females within the same genus,

it appears to me almost certain, after looking through various large

groups, that the chief agent has been the transference, in a greater or

less degree, to the female of the characters acquired by the males

through sexual selection. In the several British finches, the two sexes

differ either very slightly or considerably; and if we compare the

females of the greenfinch, chaffinch, goldfinch, bullfinch, crossbill,

sparrow, &c., we shall see that they differ from each other chiefly in

the points in which they partially resemble their respective males; and

the colours of the males may safely be attributed to sexual selection.

With many gallinaceous species the sexes differ to an extreme degree, as

with the peacock, pheasant, and fowl, whilst with other species there

has been a partial or even complete transference of character from the

male to the female. The females of the several species of Polyplectron

exhibit in a dim condition, and chiefly on the tail, the splendid ocelli

of their males. The female partridge differs from the male only in the

red mark on her breast being smaller; and the female wild turkey only in

her colours being much duller. In the guinea-fowl the two sexes are

undistinguishable. There is no improbability in the plain, though

peculiar spotted plumage of this latter bird having been acquired

through sexual selection by the males, and then transmitted to both

sexes; for it is not essentially different from the much more

beautifully-spotted plumage, characteristic of the males alone of the

Tragopan pheasants.

It should be observed that, in some instances, the transference of

characters from the male to the female has been effected apparently at a

remote period, the male having subsequently undergone great changes,

without transferring to the female any of his later-gained characters.

For instance, the female and the young of the black-grouse (_Tetrao

tetrix_) resemble pretty closely both sexes and the young of the

red-grouse _T. Scoticus_; and we may consequently infer that the

black-grouse is descended from some ancient species, of which both sexes

were coloured in nearly the same manner as the red-grouse. As both sexes

of this latter species are more plainly barred during the

breeding-season than at any other time, and as the male differs

slightly from the female in his more strongly-pronounced red and brown

tints,[238] we may conclude that his plumage has been, at least to a

certain extent, influenced by sexual selection. If so, we may further

infer that the nearly similar plumage of the female black-grouse was

similarly produced at some former period. But since this period the male

black-grouse has acquired his fine black plumage, with his forked and

outwardly-curled tail-feathers; but of these characters there has hardly

been any transference to the female, excepting that she shews in her

tail a trace of the curved fork.