GENERAL SUMMARY AND CONCLUSION.
Main conclusion that man is descended from some lower
form--Manner of development--Genealogy of man--Intellectual and
moral faculties--Sexual selection--Concluding remarks 385-405
INDEX 406
POSTSCRIPT.
Vol. I. pp. 297-299.--I have fallen into a serious and unfortunate
error, in relation to the sexual differences of animals, in attempting
to explain what seemed to me a singular coincidence in the late period
of life at which the necessary variations have arisen in many cases, and
the late period at which sexual selection acts. The explanation given is
wholly erroneous, as I have discovered by working out an illustration in
figures. Moreover, the supposed coincidence of period is far from
general, and is not remarkable; for, as I have elsewhere attempted to
show, variations arising early in life have often been accumulated
through sexual selection, being then commonly transmitted to both sexes.
On the other hand, variations arising late in life cannot fail to
coincide approximately in period with that of the process of sexual
selection. Allusions to these erroneous views reappear in Vol. II. pp.
161 and 237.
SEXUAL SELECTION.
CHAPTER XII.
SECONDARY SEXUAL CHARACTERS OF FISHES, AMPHIBIANS,
AND REPTILES.
FISHES: Courtship and battles of the males--Larger size of the
females--Males, bright colours and ornamental appendages; other
strange characters--Colours and appendages acquired by the
males during the breeding-season alone--Fishes with both sexes
brilliantly coloured--Protective colours--The less conspicuous
colours of the female cannot be accounted for on the principle
of protection--Male fishes building nests, and taking charge of
the ova and young. AMPHIBIANS: Differences in structure and
colour between the sexes--Vocal organs. REPTILES:
Chelonians--Crocodiles--Snakes, colours in some cases
protective--Lizards, battles of--Ornamental appendages--Strange
differences in structure between the sexes--Colours--Sexual
differences almost as great as with birds.
We have now arrived at the great sub-kingdom of the Vertebrata, and will
commence with the lowest class, namely Fishes. The males of
Plagiostomous fishes (sharks, rays) and of Chimaeroid fishes are provided
with claspers which serve to retain the female, like the various
structures possessed by so many of the lower animals. Besides the
claspers, the males of many rays have clusters of strong sharp spines on
their heads, and several rows along "the upper outer surface of their
pectoral fins." These are present in the males of some species, which
have the other parts of their bodies smooth. They are only temporarily
developed during the breeding-season; and Dr. Guenther suspects that they
are brought into action as prehensile organs by the doubling inwards and
downwards of the two sides of the body. It is a remarkable fact that the
females and not the males of some species, as of _Raia clavata_, have
their backs studded with large hook-formed spines.[1]
Owing to the element which fishes inhabit, little is known about their
courtship, and not much about their battles. The male stickleback
(_Gasterosteus leiurus_) has been described as "mad with delight" when
the female comes out of her hiding-place and surveys the nest which he
has made for her. "He darts round her in every direction, then to his
accumulated materials for the nest, then back again in an instant; and
as she does not advance he endeavours to push her with his snout, and
then tries to pull her by the tail and side-spine to the nest."[2] The
males are said to be polygamists;[3] they are extraordinarily bold and
pugnacious, whilst "the females are quite pacific." Their battles are at
times desperate; "for these puny combatants fasten tight on each other
for several seconds, tumbling over and over again, until their strength
appears completely exhausted." With the rough-tailed stickleback (_G.
trachurus_) the males whilst fighting swim round and round each other,
biting and endeavouring to pierce each other with their raised lateral
spines. The same writer adds,[4] "the bite of these little furies is
very severe. They also use their lateral spines with such fatal effect,
that I have seen one during a battle absolutely rip his opponent quite
open, so that he sank to the bottom and died." When a fish is conquered,
"his gallant bearing forsakes him; his gay colours fade away; and he
hides his disgrace among his peaceable companions, but is for some time
the constant object of his conqueror's persecution."
The male salmon is as pugnacious as the little stickleback; and so is
the male trout, as I hear from Dr. Guenther. Mr. Shaw saw a violent
contest between two male salmons which lasted the whole day; and Mr. R.
Buist, Superintendent of Fisheries, informs me that he has often watched
from the bridge at Perth the males driving away their rivals whilst the
females were spawning. The males "are constantly fighting and tearing
each other on the spawning-beds, and many so injure each other as to
cause the death of numbers, many being seen swimming near the banks of
the river in a state of exhaustion, and apparently in a dying state."[5]
The keeper of the Stormontfield breeding-ponds visited, as Mr. Buist
informs me, in June, 1868, the northern Tyne, and found about 300 dead
salmon, all of which with one exception were males; and he was convinced
that they had lost their lives by fighting.
[Illustration: Fig. 26. Head of male of common salmon (_Salmo salar_)
during the breeding-season.
(This drawing, as well as all the others in the present chapter, have
been executed by the well-known artist, Mr. G. Ford, under the kind
superintendence of Dr. Guenther, from specimens in the British Museum.)]
The most curious point about the male salmon is that during the
breeding-season, besides a slight change in colour, "the lower jaw
elongates, and a cartilaginous projection turns upwards from the point,
which, when the jaws are closed, occupies a deep cavity between the
intermaxillary bones of the upper jaw."[6] (Figs. 26 and 27.) In our
salmon this change of structure lasts only during the breeding-season;
but in the _Salmo lycaodon_ of N.W. America the change, as Mr. J. K.
Lord[7] believes, is permanent and best marked in the older males which
have previously ascended the rivers. In these old males the jaws become
developed into immense hook-like projections, and the teeth grow into
regular fangs, often more than half an inch in length. With the European
salmon, according to Mr. Lloyd,[8] the temporary hook-like structure
serves to strengthen and protect the jaws, when one male charges another
with wonderful violence; but the greatly developed teeth of the male
American salmon may be compared with the tusks of many male mammals, and
they indicate an offensive rather than a protective purpose.
[Illustration: Fig. 27. Head of female salmon.]
The salmon is not the only fish in which the teeth differ in the two
sexes. This is the case with many rays. In the thornback (_Raia
clavata_) the adult male has sharp, pointed teeth, directed backwards,
whilst those of the female are broad and flat, forming a pavement; so
that these teeth differ in the two sexes of the same species more than
is usual in distinct genera of the same family. The teeth of the male
become sharp only when he is adult: whilst young they are broad and flat
like those of the female. As so frequently occurs with secondary sexual
characters, both sexes of some species of rays, for instance _R. batis_,
possess, when adult, sharp, pointed teeth; and here a character, proper
to and primarily gained by the male, appears to have been transmitted to
the offspring of both sexes. The teeth are likewise pointed in both
sexes of _R. maculata_, but only when completely adult; the males
acquiring them at an earlier age than the females. We shall hereafter
meet with analogous cases with certain birds, in which the male acquires
the plumage common to both adult sexes, at a somewhat earlier age than
the female. With other species of rays the males even when old never
possess sharp teeth, and consequently both sexes when adult are provided
with broad, flat teeth like those of the young, and of the mature
females of the above-mentioned species.[9] As the rays are bold, strong
and voracious fishes, we may suspect that the males require their sharp
teeth for fighting with their rivals; but as they possess many parts
modified and adapted for the prehension of the female, it is possible
that their teeth may be used for this purpose.
In regard to size, M. Carbonnier[10] maintains that with almost all
fishes the female is larger than the male; and Dr. Guenther does not know
of a single instance in which the male is actually larger than the
female. With some Cyprinodonts the male is not even half as large as the
female. As with many kinds of fishes the males habitually fight
together; it is surprising that they have not generally become through
the effects of sexual selection larger and stronger than the females.
The males suffer from their small size, for according to M. Carbonnier
they are liable to be devoured by the females of their own species when
carnivorous, and no doubt by other species. Increased size must be in
some manner of more importance to the females, than strength and size
are to the males for fighting with other males; and this perhaps is to
allow of the production of a vast number of ova.
[Illustration: Fig. 28. Callionymus lyra. Upper figure, male; lower
figure, female.]
In many species the male alone is ornamented with bright colours; or
these are much brighter in the male than the female. The male, also, is
sometimes provided with appendages which appear to be of no more use to
him for the ordinary purposes of life than are the tail-feathers to the
peacock. I am indebted for most of the following facts to the great
kindness of Dr. Guenther. There is reason to suspect that many tropical
fishes differ sexually in colour and structure; and there are some
striking cases with our British fishes. The male _Callionymus lyra_ has
been called the _gemmeous dragonet_ "from its brilliant gem-like
colours." When freshly taken from the sea the body is yellow of various
shades, striped and spotted with vivid blue on the head; the dorsal fins
are pale brown with dark longitudinal bands; the ventral, caudal and
anal fins being bluish-black. The female, or sordid dragonet, was
considered by Linnaeus and by many subsequent naturalists as a distinct
species; it is of a dingy reddish-brown, with the dorsal fin brown and
the other fins white. The sexes differ also in the proportional size of
the head and mouth, and in the position of the eyes;[11] but the most
striking difference is the extraordinary elongation in the male (fig.
28) of the dorsal fin. The young males resemble in structure and colour
the adult females. Throughout the genus Callionymus,[12] the male is
generally much more brightly spotted than the female, and in several
species, not only the dorsal, but the anal fin of the male is much
elongated.
The male of the _Cottus scorpius_, or sea-scorpion, is more slender and
smaller than the female. There is also a great difference in colour
between them. It is difficult, as Mr. Lloyd[13] remarks, "for any one,
who has not seen this fish during the spawning-season, when its hues are
brightest, to conceive the admixture of brilliant colours with which it,
in other respects so ill-favoured, is at that time adorned." Both sexes
of the _Labrus mixtus_, although very different in colour, are
beautiful; the male being orange with bright-blue stripes, and the
female bright-red with some black spots on the back.
In the very distinct family of the Cyprinodontidae--inhabitants of the
fresh waters of foreign lands--the sexes sometimes differ much in
various characters. In the male of the _Mollienesia petenensis_,[14] the
dorsal fin is greatly developed and is marked with a row of large,
round, ocellated, bright-coloured spots; whilst the same fin in the
female is smaller, of a different shape, and marked only with
irregularly-curved brown spots. In the male the basal margin of the anal
fin is also a little produced and dark-coloured. In the male of an
allied form, the _Xiphophorus Hellerii_ (fig. 29), the inferior margin
of the anal fin is developed into a long filament, which is striped, as
I hear from Dr. Guenther, with bright colours. This filament does not
contain any muscles, and apparently cannot be of any direct use to the
fish. As in the case of the Callionymus, the males whilst young resemble
in colour and structure the adult females. Sexual differences such as
these may be strictly compared with those which are so frequent with
gallinaceous birds.[15]
[Illustration: Fig. 29. Xiphophorus Hellerii. Upper figure, male; lower
figure, female.]
In a siluroid fish, inhabiting the fresh waters of South America, namely
the _Plecostomus barbatus_[16] (fig. 30), the male has its mouth and
interoperculum fringed with a beard of stiff hairs, of which the female
shews hardly a trace. These hairs are of the nature of scales. In
another species of the same genus, soft flexible tentacles project from
the front part of the head of the male, which are absent in the
female. These tentacles are prolongations of the true skin, and
therefore are not homologous with the stiff hairs of the former species;
but it can hardly be doubted that both serve the same purpose. What this
purpose may be it is difficult to conjecture; ornament does not here
seem probable, but we can hardly suppose that stiff hairs and flexible
filaments can be useful in any ordinary way to the males alone. The
_Monacanthus scopas_, which was shewn to me in the British Museum by Dr.
Guenther, presents a nearly analogous case. The male has a cluster of
stiff, straight spines, like those of a comb, on the sides of the tail;
and these in a specimen six inches long were nearly an inch and a half
in length; the female has on the same place a cluster of bristles, which
may be compared with those of a tooth-brush. In another species, the _M.
peronii_, the male has a brush like that possessed by the female of the
last species, whilst the sides of the tail in the female are smooth. In
some other species the same part of the tail can be perceived to be a
little roughened in the male and perfectly smooth in the female; and
lastly in others, both sexes have smooth sides. In that strange monster,
the _Chimaera monstrosa_, the male has a hook-shaped bone on the top of
the head, directed forwards, with its rounded end covered with sharp
spines; in the female "this crown is altogether absent," but what its
use may be is utterly unknown.[17]
[Illustration: Fig. 30. Plecostomus barbatus. Upper figure, head of
male; lower figure, female.]
The structures as yet referred to are permanent in the male after he has
arrived at maturity; but with some Blennies and in another allied
genus[18] a crest is developed on the head of the male only during the
breeding-season, and their bodies at the same time become more
brightly-coloured. There can be little doubt that this crest serves as a
temporary sexual ornament, for the female does not exhibit a trace of
it. In other species of the same genus both sexes possess a crest, and
in at least one species neither sex is thus provided. In this case and
in that of the Monacanthus, we have good instances to how great an
extent the sexual characters of closely-allied forms may differ. In many
of the Chromidae, for instance in Geophagus and especially in Cichla, the
males, as I hear from Professor Agassiz,[19] have a conspicuous
protuberance on the forehead, which is wholly wanting in the females and
in the young males. Professor Agassiz adds, "I have often observed these
fishes at the time of spawning when the protuberance is largest, and at
other seasons when it is totally wanting and the two sexes shew no
difference whatever in the outline of the profile of the head. I never
could ascertain that it subserves any special function, and the Indians
on the Amazon know nothing about its use." These protuberances in their
periodical appearance resemble the fleshy caruncles on the heads of
certain birds; but whether they serve as ornaments must remain at
present doubtful.
The males of those fishes, which differ permanently in colour from the
females, often become more brilliant, as I hear from Professor Agassiz
and Dr. Guenther, during the breeding-season. This is likewise the case
with a multitude of fishes, the sexes of which at all other seasons of
the year are identical in colour. The tench, roach, and perch may be
given as instances. The male salmon at this season is "marked on the
cheeks with orange-coloured stripes, which give it the appearance of a
Labrus, and the body partakes of a golden-orange tinge. The females are
dark in colour, and are commonly called black-fish."[20] An analogous
and even greater change takes place with the _Salmo eriox_ or
bull-trout; the males of the char (_S. umbla_) are likewise at this
season rather brighter in colour than the females.[21] The colours of
the pike (_Esox reticulatus_) of the United States, especially of the
male, become, during the breeding-season, exceedingly intense,
brilliant, and iridescent.[22] Another striking instance out of many is
afforded by the male stickleback (_Gasterosteus leiurus_), which is
described by Mr. Warington,[23] as being then "beautiful beyond
description." The back and eyes of the female are simply brown, and the
belly white. The eyes of the male, on the other hand, are "of the most
splendid green, having a metallic lustre like the green feathers of some
humming-birds. The throat and belly are of a bright crimson, the back of
an ashy-green, and the whole fish appears as though it were somewhat
translucent and glowed with an internal incandescence." After the
breeding-season these colours all change, the throat and belly become of
a paler red, the back more green, and the glowing tints subside.
That with fishes there exists some close relation between their colours
and their sexual functions we can clearly see;--firstly, from the adult
males of certain species being differently coloured from the females,
and often much more brilliantly;--secondly, from these same males,
whilst immature, resembling the mature females;--and, lastly, from the
males, even of those species which at all other times of the year are
identical in colour with the females, often acquiring brilliant tints
during the spawning-season. We know that the males are ardent in their
courtship and sometimes fight desperately together. If we may assume
that the females have the power of exerting a choice and of selecting
the more highly-ornamented males, all the above facts become
intelligible through the principle of sexual selection. On the other
hand, if the females habitually deposited and left their ova to be
fertilised by the first male which chanced to approach, this fact would
be fatal to the efficiency of sexual selection; for there could be no
choice of a partner. But, as far as is known, the female never willingly
spawns except in the close presence of a male, and the male never
fertilises the ova except in the close presence of a female. It is
obviously difficult to obtain direct evidence with respect to female
fishes selecting their partners. An excellent observer,[24] who
carefully watched the spawning of minnows (_Cyprinus phoxinus_), remarks
that owing to the males, which were ten times as numerous as the
females, crowding closely round them, he could "speak only doubtfully on
their operations. When a female came among a number of males they
immediately pursued her; if she was not ready for shedding her spawn,
she made a precipitate retreat; but if she was ready, she came boldly in
among them, and was immediately pressed closely by a male on each side;
and when they had been in that situation a short time, were superseded
by other two, who wedged themselves in between them and the female, who
appeared to treat all her lovers with the same kindness."
Notwithstanding this last statement, I cannot, from the several previous
considerations, give up the belief that the males which are the most
attractive to the females, from their brighter colours or other
ornaments, are commonly preferred by them; and that the males have thus
been rendered more beautiful in the course of ages.
We have next to inquire whether this view can be extended, through the
law of the equal transmission of characters to both sexes, to those
groups in which the males and females are brilliant in the same or
nearly the same degree and manner. In such a genus as Labrus, which
includes some of the most splendid fishes in the world, for instance,
the Peacock Labrus (_L. pavo_), described,[25] with pardonable
exaggeration, as formed of polished scales of gold encrusting
lapis-lazuli, rubies, sapphires, emeralds and amethysts, we may, with
much probability, accept this belief; for we have seen that the sexes in
at least one species differ greatly in colour. With some fishes, as with
many of the lowest animals, splendid colours may be the direct result of
the nature of their tissues and of the surrounding conditions, without
any aid from selection. The goldfish (_Cyprinus auratus_), judging from
the analogy of the golden variety of the common carp, is, perhaps, a
case in point, as it may owe its splendid colours to a single abrupt
variation, due to the conditions to which this fish has been subjected
under confinement. It is, however, more probable that these colours have
been intensified through artificial selection, as this species has been
carefully bred in China from a remote period.[26] Under natural
conditions it does not seem probable that beings so highly organised as
fishes, and which live under such complex relations, should become
brilliantly coloured without suffering some evil or receiving some
benefit from so great a change, and consequently without the
intervention of natural selection.
What, then, must we conclude in regard to the many fishes, both sexes of
which are splendidly coloured? Mr. Wallace[27] believes that the species
which frequent reefs, where corals and other brightly-coloured organisms
abound, are brightly coloured in order to escape detection by their
enemies; but according to my recollection they were thus rendered highly
conspicuous. In the fresh-waters of the Tropics there are no
brilliantly-coloured corals or other organisms for the fishes to
resemble; yet many species in the Amazons are beautifully coloured, and
many of the carnivorous Cyprinidae in India are ornamented with "bright
longitudinal lines of various tints."[28] Mr. M'Clelland, in describing
these fishes goes so far as to suppose that "the peculiar brilliancy of
their colours" serves as "a better mark for kingfishers, terns, and
other birds which are destined to keep the number of these fishes in
check;" but at the present day few naturalists will admit that any
animal has been made conspicuous as an aid to its own destruction. It is
possible that certain fishes may have been rendered conspicuous in order
to warn birds and beasts of prey (as explained when treating of
caterpillars) that they were unpalatable; but it is not, I believe,
known that any fish, at least any freshwater fish, is rejected from
being distasteful to fish-devouring animals. On the whole, the most
probable view in regard to the fishes, of which both sexes are
brilliantly coloured, is that their colours have been acquired by the
males as a sexual ornament, and have been transferred in an equal or
nearly equal degree to the other sex.
We have now to consider whether, when the male differs in a marked
manner from the female in colour or in other ornaments, he alone has
been modified, with the variations inherited only by his male offspring;
or whether the female has been specially modified and rendered
inconspicuous for the sake of protection, such modifications being
inherited only by the females. It is impossible to doubt that colour has
been acquired by many fishes as a protection: no one can behold the
speckled upper surface of a flounder, and overlook its resemblance to
the sandy bed of the sea on which it lives. One of the most striking
instances ever recorded of an animal gaining protection by its colour
(as far as can be judged in preserved specimens) and by its form, is
that given by Dr. Guenther[29] of a pipe-fish, which, with its reddish
streaming filaments, is hardly distinguishable from the sea-weed to
which it clings with its prehensile tail. But the question now under
consideration is whether the females alone have been modified for this
object. Fishes offer valuable evidence on this head. We can see that
one sex will not be modified through natural selection for the sake of
protection more than the other, supposing both to vary, unless one sex
is exposed for a longer period to danger, or has less power of escaping
from such danger than the other sex; and it does not appear that with
fishes the sexes differ in these respects. As far as there is any
difference, the males, from being generally of smaller size, and from
wandering more about, are exposed to greater danger than the females;
and yet, when the sexes differ, the males are almost always the most
conspicuously coloured. The ova are fertilised immediately after being
deposited, and when this process lasts for several days, as in the case
of the salmon,[30] the female, during the whole time, is attended by the
male. After the ova are fertilised they are, in most cases, left
unprotected by both parents, so that the males and females, as far as
oviposition is concerned, are equally exposed to danger, and both are
equally important for the production of fertile ova; consequently the
more or less brightly-coloured individuals of either sex would be
equally liable to be destroyed or preserved, and both would have an
equal influence on the colours of their offspring or the race.
Certain fishes, belonging to several families, make nests; and some of
these fishes take care of their young when hatched. Both sexes of the
brightly-coloured _Crenilabrus massa_ and _melops_ work together in
building their nests with sea-weed, shells, &c.[31] But the males of
certain fishes do all the work, and afterwards take exclusive charge of
the young. This is the case with the dull-coloured gobies,[32] in which
the sexes are not known to differ in colour, and likewise with the
sticklebacks (Gasterosteus), in which the males become brilliantly
coloured during the spawning-season. The male of the smooth-tailed
stickleback (_G. leiurus_) performs during a long time the duties of a
nurse with exemplary care and vigilance, and is continually employed in
gently leading back the young to the nest when they stray too far. He
courageously drives away all enemies, including the females of his own
species. It would indeed be no small relief to the male if the female,
after depositing her eggs, were immediately devoured by some enemy, for
he is forced incessantly to drive her from the nest.[33]
The males of certain other fishes inhabiting South America and Ceylon,
and belonging to two distinct orders, have the extraordinary habit of
hatching the eggs laid by the females within their mouths or branchial
cavities.[34] With the Amazonian species which follow this habit, the
males, as I am informed by the kindness of Professor Agassiz, "not only
are generally brighter than the females, but the difference is greater
at the spawning-season than at any other time." The species of Geophagus
act in the same manner; and in this genus, a conspicuous protuberance
becomes developed on the forehead of the males during the
breeding-season. With the various species of Chromids, as Professor
Agassiz likewise informs me, sexual differences in colour may be
observed, "whether they lay their eggs in the water among aquatic
plants, or deposit them in holes, leaving them to come out without
further care, or build shallow nests in the river-mud, over which they
sit, as our Promotis does. It ought also to be observed that these
sitters are among the brightest species in their respective families;
for instance, Hygrogonus is bright green, with large black ocelli,
encircled with the most brilliant red." Whether with all the species of
Chromids it is the male alone which sits on the eggs is not known. It
is, however, manifest that the fact of the eggs being protected or
unprotected, has had little or no influence on the differences in colour
between the sexes. It is further manifest, in all the cases in which the
males take exclusive charge of the nests and young, that the destruction
of the brighter-coloured males would be far more influential on the
character of the race, than the destruction of the brighter-coloured
females; for the death of the male during the period of incubation or
nursing would entail the death of the young, so that these could not
inherit his peculiarities; yet, in many of these very cases the males
are more conspicuously coloured than the females.
In most of the Lophobranchii (Pipe-fish, Hippocampi, &c.) the males have
either marsupial sacks or hemispherical depressions on the abdomen, in
which the ova laid by the female are hatched. The males also shew great
attachment to their young.[35] The sexes do not commonly differ much in
colour; but Dr. Guenther believes that the male Hippocampi are rather
brighter than the females. The genus Solenostoma, however, offers a
very curious exceptional case,[36] for the female is much more vividly
coloured and spotted than the male, and she alone has a marsupial sack
and hatches the eggs; so that the female of Solenostoma differs from all
the other Lophobranchii in this latter respect, and from almost all
other fishes, in being more brightly coloured than the male. It is
improbable that this remarkable double inversion of character in the
female should be an accidental coincidence. As the males of several
fishes which take exclusive charge of the eggs and young are more
brightly coloured than the females, and as here the female Solenostoma
takes the same charge and is brighter than the male, it might be argued
that the conspicuous colours of the sex which is the most important of
the two for the welfare of the offspring must serve, in some manner, as
a protection. But from the multitude of fishes, the males of which are
either permanently or periodically brighter than the females, but whose
life is not at all more important than that of the female for the
welfare of the species, this view can hardly be maintained. When we
treat of birds we shall meet with analogous cases in which there has
been a complete inversion of the usual attributes of the two sexes, and
we shall then give what appears to be the probable explanation, namely,
that the males have selected the more attractive females, instead of the
latter having selected, in accordance with the usual rule throughout the
animal kingdom, the more attractive males.
On the whole we may conclude, that with most fishes, in which the sexes
differ in colour or in other ornamental characters, the males
originally varied, with their variations transmitted to the same sex,
and accumulated through sexual selection by attracting or exciting the
females. In many cases, however, such characters have been transferred,
either partially or completely, to the females. In other cases, again,
both sexes have been coloured alike for the sake of protection; but in
no instance does it appear that the female alone has had her colours or
other characters specially modified for this purpose.
The last point which need be noticed is that in many parts of the world
fishes are known to make peculiar noises, which are described in some
cases as being musical. Very little has been ascertained with respect to
the means by which such sounds are produced, and even less about their
purpose. The drumming of the Umbrinas in the European seas is said to be
audible from a depth of twenty fathoms. The fishermen of Rochelle assert
"that the males alone make the noise during the spawning-time; and that
it is possible by imitating it, to take them without bait."[37] If this
statement is trustworthy, we have an instance in this, the lowest class
of the Vertebrata, of what we shall find prevailing throughout the other
vertebrate classes, and which prevails, as we have already seen, with
insects and spiders; namely, that vocal and instrumental sounds so
commonly serve as a love-call or as a love-charm, that the power of
producing them was probably first developed in connection with the
propagation of the species.
AMPHIBIANS.
[Illustration: Fig. 31. Triton cristatus (half natural size, from Bell's
'British Reptiles'). Upper figure, male during the breeding-season;
lower figure, female.]
_Urodela._--First for the tailed amphibians. The sexes of salamanders or
newts often differ much both in colour and structure. In some species
prehensile claws are developed on the forelegs of the males during the
breeding-season; and at this season in the male _Triton palmipes_ the
hind-feet are provided with a swimming web, which is almost completely
absorbed during the winter; so that their feet then resemble those of
the female.[38] This structure no doubt aids the male in his eager
search and pursuit of the female. With our common newts (_Triton
punctatus_ and _cristatus_) a deep, much-indented crest is developed
along the back and tail of the male during the breeding-season, being
absorbed during the winter. It is not furnished, as Mr. St. George
Mivart informs me, with muscles, and therefore cannot be used for
locomotion. As during the season of courtship it becomes edged with
bright colours, it serves, there can hardly be a doubt, as a masculine
ornament. In many species the body presents strongly contrasted, though
lurid tints; and these become more vivid during the breeding-season. The
male, for instance, of our common little newt (_Triton punctatus_) is
"brownish-grey above, passing into yellow beneath, which in the spring
becomes a rich bright orange, marked everywhere with round dark spots."
The edge of the crest also is then tipped with bright red or violet. The
female is usually of a yellowish-brown colour with scattered brown dots;
and the lower surface is often quite plain.[39] The young are obscurely
tinted. The ova are fertilised during the act of deposition and are not
subsequently tended by either parent. We may therefore conclude that the
males acquired their strongly-marked colours and ornamental appendages
through sexual selection; these being transmitted either to the male
offspring alone or to both sexes.
_Anura_ or _Batrachia_.--With many frogs and toads the colours evidently
serve as a protection, such as the bright green tints of tree-frogs and
the obscure mottled shades of many terrestrial species. The most
conspicuously coloured toad which I ever saw, namely the _Phryniscus
nigricans_[40] had the whole upper surface of the body as black as ink,
with the soles of the feet and parts of the abdomen spotted with the
brightest vermilion. It crawled about the bare sandy or open grassy
plains of La Plata under a scorching sun, and could not fail to catch
the eye of every passing creature. These colours may be beneficial by
making this toad known to all birds of prey as a nauseous mouthful; for
it is familiar to every one that these animals emit a poisonous
secretion, which causes the mouth of a dog to froth, as if attacked by
hydrophobia. I was the more struck with the conspicuous colours of this
toad, as close by I found a lizard (_Proctotretus multimaculatus_)
which, when frightened, flattened its body, closed its eyes, and then
from its mottled tints could hardly be distinguishable from the
surrounding sand.
With respect to sexual differences of colour, Dr. Guenther knows of no
striking instance with frogs or toads; yet he can often distinguish the
male from the female, by the tints of the former being a little more
intense. Nor does Dr. Guenther know of any striking difference in
external structure between the sexes, excepting the prominences which
become developed during the breeding-season on the front-legs of the
male, by which he is enabled to hold the female. The _Megalophrys
montana_[41] (fig. 32) offers the best case of a certain amount of
structural difference between the sexes; for in the male the tip of the
nose and the eyelids are produced into triangular flaps of skin, and
there is a little black tubercle on the back--characters which are
absent, or only feebly developed, in the females. It is surprising that
frogs and toads should not have acquired more strongly-marked sexual
differences; for though cold-blooded, their passions are strong. Dr.
Guenther informs me that he has several times found an unfortunate female
toad dead and smothered from having been so closely embraced by three or
four males.
[Illustration: Fig. 32. Megalophrys montana. The two left-hand figures,
the male; the two right-hand figures, the female.]
These animals, however, offer one interesting sexual difference, namely
in the musical powers possessed by the males; but to speak of music,
when applied to the discordant and overwhelming sounds emitted by male
bull-frogs and some other species, seems, according to our taste, a
singularly inappropriate expression. Nevertheless certain frogs sing in
a decidedly pleasing manner. Near Rio de Janeiro I used often to sit in
the evening to listen to a number of little Hylae, which, perched on
blades of grass close to the water, sent forth sweet chirping notes in
harmony. The various sounds are emitted chiefly by the males during the
breeding-season, as in the case of the croaking of our common frog.[42]
In accordance with this fact the vocal organs of the males are more
highly developed than those of the females. In some genera the males
alone are provided with sacs which open into the larynx.[43] For
instance, in the edible frog (_Rana esculenta_) "the sacs are peculiar
to the males, and become, when filled with air in the act of croaking,
large globular bladders, standing out one on each side of the head, near
the corners of the mouth." The croak of the male is thus rendered
exceedingly powerful; whilst that of the female is only a slight
groaning noise.[44] The vocal organs differ considerably in structure in
the several genera of the family; and their development in all cases may
be attributed to sexual selection.
REPTILES.
_Chelonia._--Tortoises and turtles do not offer well-marked sexual
differences. In some species, the tail of the male is longer than that
of the female. In some, the plastron or lower surface of the shell of
the male is slightly concave in relation to the back of the female. The
male of the mud-turtle of the United States (_Chrysemys picta_) has
claws on its front-feet twice as long as those of the female; and these
are used when the sexes unite.[45] With the huge tortoise of the
Galapagos Islands (_Testudo nigra_) the males are said to grow to a
larger size than the females: during the pairing-season, and at no other
time, the male utters a hoarse, bellowing noise, which can be heard at
the distance of more than a hundred yards; the female, on the other
hand, never uses her voice.[46]
_Crocodilia._--The sexes apparently do not differ in colour; nor do I
know that the males fight together, though this is probable, for some
kinds make a prodigious display before the females. Bartram[47]
describes the male alligator as striving to win the female by splashing
and roaring in the midst of a lagoon, "swollen to an extent ready to
burst, with his head and tail lifted up, he spins or twirls round on the
surface of the water, like an Indian chief rehearsing his feats of war."
During the season of love, a musky odour is emitted by the submaxillary
glands of the crocodile, and pervades their haunts.[48]
_Ophidia._--I have little to say about Snakes. Dr. Guenther informs me
that the males are always smaller than the females, and generally have
longer and slenderer tails; but he knows of no other difference in
external structure. In regard to colour, Dr. Guenther can almost always
distinguish the male from the female by his more strongly-pronounced
tints; thus the black zigzag band on the back of the male English viper
is more distinctly defined than in the female. The difference is much
plainer in the Rattle-snakes of N. America, the male of which, as the
keeper in the Zoological Gardens shewed me, can instantly be
distinguished from the female by having more lurid yellow about its
whole body. In S. Africa the _Bucephalus capensis_ presents an analogous
difference, for the female "is never so fully variegated with yellow on
the sides, as the male."[49] The male of the Indian _Dipsas cynodon_, on
the other hand, is blackish-brown, with the belly partly black, whilst
the female is reddish or yellowish-olive with the belly either uniform
yellowish or marbled with black.
In the _Tragops dispar_ of the same country, the male is bright green,
and the female bronze-coloured.[50] No doubt the colours of some snakes
serve as a protection, as the green tints of tree-snakes and the various
mottled shades of the species which live in sandy places; but it is
doubtful whether the colours of many kinds, for instance of the common
English snake or viper, serve to conceal them; and this is still more
doubtful with the many foreign species which are coloured with extreme
elegance.
During the breeding-season their anal scent-glands are in active
function;[51] and so it is with the same glands in lizards, and as we
have seen with the submaxillary glands of crocodiles. As the males of
most animals search for the females, these odoriferous glands probably
serve to excite or charm the female, rather than to guide her to the
spot where the male may be found.[52] Male snakes, though appearing so
sluggish, are amorous; for many have been observed crowding round the
same female, and even round the dead body of a female. They are not
known to fight together from rivalry. Their intellectual powers are
higher than might have been anticipated. An excellent observer in
Ceylon, Mr. E. Layard,[53] saw a Cobra thrust its head through a narrow
hole and swallow a toad. "With this incumbrance he could not withdraw
himself; finding this, he reluctantly disgorged the precious morsel,
which began to move off; this was too much for snake philosophy to bear,
and the toad was again seized, and again was the snake, after violent
efforts to escape, compelled to part with its prey. This time, however,
a lesson had been learnt, and the toad was seized by one leg, withdrawn,
and then swallowed in triumph."
It does not, however, follow because snakes have some reasoning power
and strong passions, that they should likewise be endowed with
sufficient taste to admire brilliant colours in their partners, so as to
lead to the adornment of the species through sexual selection.
Nevertheless it is difficult to account in any other manner for the
extreme beauty of certain species; for instance, of the coral-snakes of
S. America, which are of a rich red with black and yellow transverse
bands. I well remember how much surprise I felt at the beauty of the
first coral-snake which I saw gliding across a path in Brazil. Snakes
coloured in this peculiar manner, as Mr. Wallace states on the authority
of Dr. Guenther,[54] are found nowhere else in the world except in S.
America, and here no less than four genera occur. One of these, Elaps,
is venomous; a second and widely-distinct genus is doubtfully venomous,
and the two others are quite harmless. The species belonging to these
distinct genera inhabit the same districts, and are so like each other,
that no one "but a naturalist would distinguish the harmless from the
poisonous kinds." Hence, as Mr. Wallace believes, the innocuous kinds
have probably acquired their colours as a protection, on the principle
of imitation; for they would naturally be thought dangerous by their
enemies. The cause, however, of the bright colours of the venomous Elaps
remains to be explained, and this may perhaps be sexual selection.
_Lacertilia._--The males of some, probably of many kinds of lizards
fight together from rivalry. Thus the arboreal _Anolis cristatellus_ of
S. America is extremely pugnacious: "During the spring and early part of
the summer, two adult males rarely meet without a contest. On first
seeing one another, they nod their heads up and down three or four
times, at the same time expanding the frill or pouch beneath the throat;
their eyes glisten with rage, and after waving their tails from side to
side for a few seconds, as if to gather energy, they dart at each other
furiously, rolling over and over, and holding firmly with their teeth.
The conflict generally ends in one of the combatants losing his tail,
which is often devoured by the victor." The male of this species is
considerably larger than the female;[55] and this, as far as Dr. Guenther
has been able to ascertain, is the general rule with lizards of all
kinds.
The sexes often differ greatly in various external characters. The male
of the above-mentioned Anolis is furnished with a crest, which runs
along the back and tail, and can be erected at pleasure; but of this
crest the female does not exhibit a trace. In the Indian _Cophotis
ceylanica_, the female possesses a dorsal crest, though much less
developed than in the male; and so it is, as Dr. Guenther informs me,
with the females of many Iguanas, Chameleons and other lizards. In some
species, however, the crest is equally developed in both sexes, as in
the _Iguana tuberculata_. In the genus Sitana, the males alone are
furnished with a large throat-pouch (fig. 33), which can be folded up
like a fan, and is coloured blue, black, and red; but these splendid
colours are exhibited only during the pairing-season. The female does
not possess even a rudiment of this appendage. In the _Anolis
cristatellus_, according to Mr. Austen, the throat-pouch, which is
bright red marbled with yellow, is present, though in a rudimental
condition, in the female. Again, in certain other lizards, both sexes
are equally well provided with throat-pouches. Here, as in so many
previous cases, we see with species belonging to the same group, the
same character confined to the males, or more largely developed in the
males than in the females, or equally developed in both sexes. The
little lizards of the genus Draco, which glide through the air on their
rib-supported parachutes, and which in the beauty of their colours
baffle description, are furnished with skinny appendages to the throat,
"like the wattles of gallinaceous birds." These become erected when the
animal is excited. They occur in both sexes, but are best developed in
the male when arrived at maturity, at which age the middle appendage is
sometimes twice as long as the head. Most of the species likewise have a
low crest running along the neck; and this is much more developed in the
full-grown males, than in the females or young males.[56]
[Illustration: Fig. 33. Sitana minor. Male, with the gular pouch
expanded (from Guenther's 'Reptiles of India').]
There are other and much more remarkable differences between the sexes
of certain lizards. The male of _Ceratophora aspera_ bears on the
extremity of his snout an appendage half as long as the head. It is
cylindrical, covered with scales, flexible, and apparently capable of
erection: in the female it is quite rudimental. In a second species of
the same genus a terminal scale forms a minute horn on the summit of the
flexible appendage; and in a third species (_C. Stoddartii_, fig. 34)
the whole appendage is converted into a horn, which is usually of a
white colour, but assumes a purplish tint when the animal is excited. In
the adult male of this latter species the horn is half an inch in
length, but is of quite minute size in the female and in the young.
These appendages, as Dr. Guenther has remarked to me, may be compared
with the combs of gallinaceous birds, and apparently serve as ornaments.
[Illustration: Fig. 34. Ceratophora Stoddartii. Upper figure, male;
lower figure, female.]
[Illustration: Fig. 35. Chamaeleon bifurcus. Upper figure, male; lower
figure, female.]
In the genus Chamaeleon we come to the climax of difference between the
sexes. The upper part of the skull of the male _C. bifurcus_ (fig. 35),
an inhabitant of Madagascar, is produced into two great, solid, bony
projections, covered with scales like the rest of the head; and of this
wonderful modification of structure the female exhibits only a rudiment.
Again, in _Chamaeleon Owenii_ (fig. 36), from the West Coast of Africa,
the male bears on his snout and forehead three curious horns, of which
the female has not a trace. These horns consist of an excrescence of
bone covered with a smooth sheath, forming part of the general
integuments of the body, so that they are identical in structure with
those of a bull, goat, or other sheath-horned ruminant. Although the
three horns differ so much in appearance from the two great
prolongations of the skull in _C. bifurcus_, we can hardly doubt that
they serve the same general purpose in the economy of these two animals.
The first conjecture which will occur to every one is that they are
used by the males for fighting together; but Dr. Guenther, to whom I am
indebted for the foregoing details, does not believe that such peaceable
creatures would ever become pugnacious. Hence we are driven to infer
that these almost monstrous deviations of structure serve as masculine
ornaments.
[Illustration: Fig. 36. Chamaeleon Owenii. Upper figure, male; lower
figure, female.]
With many kinds of lizards, the sexes differ slightly in colour, the
tints and stripes of the males being brighter and more distinctly
defined than in the females. This, for instance, is the case with the
previously-mentioned Cophotis and with the _Acanthodactylus capensis_ of
S. Africa. In a Cordylus of the latter country, the male is either much
redder or greener than the female. In the Indian _Calotes nigrilabris_
there is a greater difference in colour between the sexes; the lips also
of the male are black, whilst those of the female are green. In our
common little viviparous lizard (_Zootoca vivipara_) "the under side of
the body and base of the tail in the male are bright orange, spotted
with black; in the female these parts are pale greyish-green without
spots."[57] We have seen that the males alone of Sitana possess a
throat-pouch; and this is splendidly tinted with blue, black, and red.
In the _Proctotretus tenuis_ of Chile the male alone is marked with
spots of blue, green, and coppery-red.[58] I collected in S. America
fourteen species of this genus, and though I neglected to record the
sexes, I observed that certain individuals alone were marked with
emerald-like green spots, whilst others had orange-coloured gorges; and
these in both cases no doubt were the males.
In the foregoing species, the males are more brightly coloured than the
females, but with many lizards both sexes are coloured in the same
elegant or even magnificent manner; and there is no reason to suppose
that such conspicuous colours are protective. With some lizards,
however, the green tints no doubt serve for concealment; and an instance
has already been incidently given of one species of Proctotretus which
closely resembles the sand on which it lives. On the whole we may
conclude with tolerable safety that the beautiful colours of many
lizards, as well as various appendages and other strange modifications
of structure, have been gained by the males through sexual selection for
the sake of ornament, and have been transmitted either to their male
offspring alone or to both sexes. Sexual selection, indeed, seems to
have played almost as important a part with reptiles as with birds. But
the less conspicuous colours of the females in comparison with those of
the males cannot be accounted for, as Mr. Wallace believes to be the
case with birds, by the exposure of the females to danger during
incubation.
CHAPTER XIII.
SECONDARY SEXUAL CHARACTERS OF BIRDS.
Sexual differences--Law of battle--Special weapons--Vocal
organs--Instrumental music--Love-antics and
dances--Decorations, permanent and seasonal--Double and single
annual moults--Display of ornaments by the males.
Secondary sexual characters are more diversified and conspicuous in
birds, though not perhaps entailing more important changes of structure,
than in any other class of animals. I shall, therefore, treat the
subject at considerable length. Male birds sometimes, though rarely,
possess special weapons for fighting with each other. They charm the
females by vocal or instrumental music of the most varied kinds. They
are ornamented by all sorts of combs, wattles, protuberances, horns,
air-distended sacs, top-knots, naked shafts, plumes and lengthened
feathers gracefully springing from all parts of the body. The beak and
naked skin about the head, and the feathers are often gorgeously
coloured. The males sometimes pay their court by dancing, or by
fantastic antics performed either on the ground or in the air. In one
instance, at least, the male emits a musky odour which we may suppose
serves to charm or excite the female; for that excellent observer, Mr.
Ramsay,[59] says of the Australian musk-duck (_Biziura lobata_) that
"the smell which the male emits during the summer months is confined to
that sex, and in some individuals is retained throughout the year; I
have never even in the breeding-season, shot a female which had any
smell of musk." So powerful is this odour during the pairing-season,
that it can be detected long before the bird can be seen.[60] On the
whole, birds appear to be the most aesthetic of all animals, excepting of
course man, and they have nearly the same taste for the beautiful as we
have. This is shewn by our enjoyment of the singing of birds, and by our
women, both civilised and savage, decking their heads with borrowed
plumes, and using gems which are hardly more brilliantly coloured than
the naked skin and wattles of certain birds.
Before treating of the characters with which we are here more
particularly concerned, I may just allude to certain differences between
the sexes which apparently depend on differences in their habits of
life; for such cases, though common in the lower, are rare in the higher
classes. Two humming-birds belonging to the genus Eustephanus, which
inhabit the island of Juan Fernandez, were long thought to be
specifically distinct, but are now known, as Mr. Gould informs me, to be
the sexes of the same species, and they differ slightly in the form of
the beak. In another genus of humming-birds (_Grypus_), the beak of the
male is serrated along the margin and hooked at the extremity, thus
differing much from that of the female. In the curious Neomorpha of New
Zealand, there is a still wider difference in the form of the beak; and
Mr. Gould has been informed that the male with his "straight and stout
beak" tears off the bark of trees, in order that the female may feed on
the uncovered larvae with her weaker and more curved beak. Something of
the same kind may be observed with our goldfinch (_Carduelis elegans_),
for I am assured by Mr. J. Jenner Weir that the bird-catchers can
distinguish the males by their slightly longer beaks. The flocks of
males, as an old and trustworthy bird-catcher asserted, are commonly
found feeding on the seeds of the teazle (Dipsacus) which they can reach
with their elongated beaks, whilst the females more commonly feed on the
seeds of the betony or Scrophularia. With a slight difference of this
nature as a foundation, we can see how the beaks of the two sexes might
be made to differ greatly through natural selection. In all these cases,
however, especially in that of the quarrelsome humming-birds, it is
possible that the differences in the beaks may have been first acquired
by the males in relation to their battles, and afterwards led to
slightly changed habits of life.
_Law of Battle._--Almost all male birds are extremely pugnacious, using
their beaks, wings, and legs for fighting together. We see this every
spring with our robins and sparrows. The smallest of all birds, namely
the humming-bird, is one of the most quarrelsome. Mr. Gosse[61]
describes a battle, in which a pair of humming-birds seized hold of each
other's beaks, and whirled round and round, till they almost fell to the
ground; and M. Montes de Oca, in speaking of another genus, says that
two males rarely meet without a fierce aerial encounter: when kept in
cages "their fighting has mostly ended in the splitting of the tongue of
one of the two, which then surely dies from being unable to feed."[62]
With Waders, the males of the common water-hen (_Gallinula chloropus_)
"when pairing, fight violently for the females: they stand nearly
upright in the water and strike with their feet." Two were seen to be
thus engaged for half an hour, until one got hold of the head of the
other which would have been killed, had not the observer interfered; the
female all the time looking on as a quiet spectator.[63] The males of an
allied bird (_Gallicrex cristatus_), as Mr. Blyth informs me, are one
third larger than the females, and are so pugnacious during the
breeding-season, that they are kept by the natives of Eastern Bengal for
the sake of fighting. Various other birds are kept in India for the same
purpose, for instance the Bulbuls (_Pycnonotus haemorrhous_) which "fight
with great spirit."[64]
The polygamous Ruff (_Machetes pugnax_, fig. 37) is notorious for his
extreme pugnacity; and in the spring, the males, which are considerably
larger than the females, congregate day after day at a particular spot,
where the females propose to lay their eggs. The fowlers discover these
spots by the turf being trampled somewhat bare. Here they fight very
much like game-cocks, seizing each other with their beaks and striking
with their wings. The great ruff of feathers round the neck is then
erected, and according to Col. Montagu "sweeps the ground as a shield to
defend the more tender parts;" and this is the only instance known to me
in the case of birds, of any structure serving as a shield. The ruff of
feathers, however, from its varied and rich colours probably serves in
chief part as an ornament. Like most pugnacious birds, they seem always
ready to fight, and when closely confined often kill each other; but
Montagu observed that their pugnacity becomes greater during the spring,
when the long feathers on their necks are fully developed; and at this
period the least movement by any one bird provokes a general
battle.[65] Of the pugnacity of web-footed birds, two instances will
suffice: in Guiana "bloody fights occur during the breeding-season
between the males of the wild musk-duck (_Cairina moschata_); and where
these fights have occurred the river is covered for some distance with
feathers."[66] Birds which seem ill-adapted for fighting engage in
fierce conflicts; thus with the pelican the stronger males drive away
the weaker ones, snapping with their huge beaks and giving heavy blows
with their wings. Male snipes fight together, "tugging and pushing each
other with their bills in the most curious manner imaginable." Some few
species are believed never to fight; this is the case, according to
Audubon, with one of the woodpeckers of the United States (_Picus
auratus_), although "the hens are followed by even half a dozen of their
gay suitors."[67]
[Illustration: Fig. 37. The Ruff or Machetes pugnax (from Brehm's
'Thierleben').]
The males of many birds are larger than the females, and this no doubt
is an advantage to them in their battles with their rivals, and has been
gained through sexual selection. The difference in size between the two
sexes is carried to an extreme point in several Australian species; thus
the male musk-duck (Biziura) and the male _Cincloramphus cruralis_
(allied to our pipits) are by measurement actually twice as large as
their respective females.[68] With many other birds the females are
larger than the males; and as formerly remarked, the explanation often
given, namely that the females have most of the work in feeding their
young, will not suffice. In some few cases, as we shall hereafter see,
the females apparently have acquired their greater size and strength for
the sake of conquering other females and obtaining possession of the
males.
The males of many gallinaceous birds, especially of the polygamous
kinds, are furnished with special weapons for fighting with their
rivals, namely spurs, which can be used with fearful effect. It has been
recorded by a trustworthy writer[69] that in Derbyshire a kite struck at
a game-hen accompanied by her chickens, when the cock rushed to the
rescue and drove his spur right through the eye and skull of the
aggressor. The spur was with difficulty drawn from the skull, and as the
kite though dead retained his grasp, the two birds were firmly locked
together; but the cock when disentangled was very little injured. The
invincible courage of the game-cock is notorious: a gentleman who long
ago witnessed the following brutal scene, told me that a bird had both
its legs broken by some accident in the cock-pit, and the owner laid a
wager that if the legs could be spliced so that the bird could stand
upright, he would continue fighting. This was effected on the spot, and
the bird fought with undaunted courage until he received his
death-stroke. In Ceylon a closely-allied and wild species, the _Gallus
Stanleyi_, is known to fight desperately "in defence of his seraglio,"
so that one of the combatants is frequently found dead.[70] An Indian
partridge (_Ortygornis gularis_), the male of which is furnished with
strong and sharp spurs, is so quarrelsome, "that the scars of former
fights disfigure the breast of almost every bird you kill."[71]
The males of almost all gallinaceous birds, even those which are not
furnished with spurs, engage during the breeding-season in fierce
conflicts. The Capercailzie and Black-cock (_Tetrao urogallus_ and _T.
tetrix_), which are both polygamists, have regular appointed places,
where during many weeks they congregate in numbers to fight together and
to display their charms before the females. M. W. Kowalevsky informs me
that in Russia he has seen the snow all bloody on the arenas where the
Capercailzie have fought; and the Black-cocks "make the feathers fly in
every direction," when several "engage in a battle royal." The elder
Brehm gives a curious account of the Balz, as the love-dance and
love-song of the Black-cock is called in Germany. The bird utters almost
continuously the most strange noises: "he holds his tail up and spreads
it out like a fan, he lifts up his head and neck with all the feathers
erect, and stretches his wings from the body. Then he takes a few jumps
in different directions, sometimes in a circle, and presses the under
part of his beak so hard against the ground that the chin-feathers are
rubbed off. During these movements he beats his wings and turns round
and round. The more ardent he grows the more lively he becomes, until at
last the bird appears like a frantic creature." At such times the
black-cocks are so absorbed that they become almost blind and deaf, but
less so than the capercailzie: hence bird after bird may be shot on the
same spot, or even caught by the hand. After performing these antics the
males begin to fight: and the same black-cock, in order to prove his
strength over several antagonists, will visit in the course of one
morning several Balz-places, which remain the same during successive
years.[72]
The peacock with his long train appears more like a dandy than a
warrior, but he sometimes engages in fierce contests: the Rev. W. Darwin
Fox informs me that two peacocks became so excited whilst fighting at
some little distance from Chester that they flew over the whole city,
still fighting, until they alighted on the top of St. John's tower.
The spur, in those gallinaceous birds which are thus provided, is
generally single; but Polyplectron (see fig. 51, p. 90) has two or more
on each leg; and one of the Blood-pheasants (_Ithaginis cruentus_) has
been seen with five spurs. The spurs are generally confined to the male,
being represented by mere knobs or rudiments in the female; but the
females of the Java peacock (_Pavo muticus_) and, as I am informed by
Mr. Blyth, of the small fire-backed pheasant (_Euplocamus
erythropthalmus_) possess spurs. In Galloperdix it is usual for the
males to have two spurs, and for the females to have only one on each
leg.[73] Hence spurs may safely be considered as a masculine character,
though occasionally transferred in a greater or less degree to the
females. Like most other secondary sexual characters, the spurs are
highly variable both in number and development in the same species.
[Illustration: Fig. 38. Palamedea cornuta (from Brehm), shewing the
double-wing-spurs, and the filament on the head.]
Various birds have spurs on their wings. But the Egyptian goose
(_Chenalopex aegyptiacus_) has only "bare obtuse knobs," and these
probably shew us the first steps by which true spurs have been developed
in other allied birds. In the spur-winged goose, _Plectropterus
gambensis_, the males have much larger spurs than the females; and they
use them, as I am informed by Mr. Bartlett, in fighting together, so
that, in this case, the wing-spurs serve as sexual weapons; but
according to Livingstone, they are chiefly used in the defence of the
young. The Palamedea (fig. 38) is armed with a pair of spurs on each
wing; and these are such formidable weapons that a single blow has
driven a dog howling away. But it does not appear that the spurs in this
case, or in that of some of the spur-winged rails, are larger in the
male than in the female.[74] In certain plovers, however, the wing-spurs
must be considered as a sexual character. Thus in the male of our common
peewit (_Vanellus cristatus_) the tubercle on the shoulder of the wing
becomes more prominent during the breeding-season, and the males are
known to fight together. In some species of Lobivanellus a similar
tubercle becomes developed during the breeding-season "into a short
horny spur." In the Australian _L. lobatus_ both sexes have spurs, but
these are much larger in the males than in the females. In an allied
bird, the _Hoplopterus armatus_, the spurs do not increase in size
during the breeding-season; but these birds have been seen in Egypt to
fight together, in the same manner as our peewits, by turning suddenly
in the air and striking sideways at each other, sometimes with a fatal
result. Thus also they drive away other enemies.[75]
The season of love is that of battle; but the males of some birds, as of
the game-fowl and ruff, and even the young males of the wild turkey and
grouse,[76] are ready to fight whenever they meet. The presence of the
female is the _teterrima belli causa_. The Bengali baboos make the
pretty little males of the amadavat (_Estrelda amandava_) fight together
by placing three small cages in a row, with a female in the middle;
after a little time the two males are turned loose, and immediately a
desperate battle ensues.[77] When many males congregate at the same
appointed spot and fight together, as in the case of grouse and various
other birds, they are generally attended by the females,[78] which
afterwards pair with the victorious combatants. But in some cases the
pairing precedes instead of succeeding the combat: thus, according to
Audubon,[79] several males of the Virginian goat-sucker (_Caprimulgus
Virginianus_) "court, in a highly entertaining manner, the female, and
no sooner has she made her choice, than her approved gives chase to all
intruders, and drives them beyond his dominions." Generally the males
try with all their power to drive away or kill their rivals before they
pair. It does not, however, appear that the females invariably prefer
the victorious males. I have indeed been assured by M. W. Kowalevsky
that the female capercailzie sometimes steals away with a young male who
has not dared to enter the arena with the older cocks; in the same
manner as occasionally happens with the does of the red-deer in
Scotland. When two males contend in presence of a single female, the
victor, no doubt, commonly gains his desire; but some of these battles
are caused by wandering males trying to distract the peace of an already
mated pair.[80]
Even with the most pugnacious species it is probable that the pairing
does not depend exclusively on the mere strength and courage of the
male: for such males are generally decorated with various ornaments,
which often become more brilliant during the breeding-season, and which
are sedulously displayed before the females. The males also endeavour to
charm or excite their mates by love-notes, songs, and antics; and the
courtship is, in many instances, a prolonged affair. Hence it is not
probable that the females are indifferent to the charms of the opposite
sex, or that they are invariably compelled to yield to the victorious
males. It is more probable that the females are excited, either before
or after the conflict, by certain males, and thus unconsciously prefer
them. In the case of _Tetrao umbellus_, a good observer[81] goes so far
as to believe that the battles of the males "are all a sham, performed
to show themselves to the greatest advantage before the admiring females
who assemble around; for I have never been able to find a maimed hero,
and seldom more than a broken feather." I shall have to recur to this
subject, but I may here add that with the _Tetrao cupido_ of the United
States, about a score of males assemble at a particular spot, and
strutting about make the whole air resound with their extraordinary
noises. At the first answer from a female the males begin to fight
furiously, and the weaker give way; but then, according to Audubon, both
the victors and vanquished search for the female, so that the females
must either then exert a choice, or the battle must be renewed. So,
again, with one of the Field-starlings of the United States (_Sturnella
ludoviciana_) the males engage in fierce conflicts, "but at the sight of
a female they all fly after her, as if mad."[82]
_Vocal and instrumental Music._--With birds the voice serves to express
various emotions, such as distress, fear, anger, triumph, or mere
happiness. It is apparently sometimes used to excite terror, as with the
hissing noise made by some nestling-birds. Audubon[83] relates that a
night-heron (_Ardea nycticorax_, Linn.) which he kept tame, used to hide
itself when a cat approached, and then "suddenly start up uttering one
of the most frightful cries, apparently enjoying the cat's alarm and
flight." The common domestic cock clucks to the hen, and the hen to her
chickens, when a dainty morsel is found. The hen, when she has laid an
egg, "repeats the same note very often, and concludes with the sixth
above, which she holds for a longer time;"[84] and thus she expresses
her joy. Some social birds apparently call to each other for aid; and as
they flit from tree to tree, the flock is kept together by chirp
answering chirp. During the nocturnal migrations of geese and other
water-fowl, sonorous clangs from the van may be heard in the darkness
overhead, answered by clangs in the rear. Certain cries serve as
danger-signals, which, as the sportsman knows to his cost, are well
understood by the same species and by others. The domestic cock crows,
and the humming-bird chirps, in triumph over a defeated rival. The true
song, however, of most birds and various strange cries are chiefly
uttered during the breeding-season, and serve as a charm, or merely as a
call-note, to the other sex.
Naturalists are much divided with respect to the object of the singing
of birds. Few more careful observers ever lived than Montagu, and he
maintained that the "males of song-birds and of many others do not in
general search for the female, but, on the contrary, their business in
the spring is to perch on some conspicuous spot breathing out their full
and amorous notes, which, by instinct, the female knows, and repairs to
the spot to choose her mate."[85] Mr. Jenner Weir informs me that this
is certainly the case with the nightingale. Bechstein, who kept birds
during his whole life, asserts, "that the female canary always chooses
the best singer, and that in a state of nature the female finch selects
that male out of a hundred whose notes please her most."[86] There can
be no doubt that birds closely attend to each other's song. Mr. Weir has
told me of the case of a bullfinch which had been taught to pipe a
German waltz, and who was so good a performer that he cost ten guineas;
when this bird was first introduced into a room where other birds were
kept and he began to sing, all the others, consisting of about twenty
linnets and canaries, ranged themselves on the nearest side of their
cages, and listened with the greatest interest to the new performer.
Many naturalists believe that the singing of birds is almost exclusively
"the effect of rivalry and emulation," and not for the sake of charming
their mates. This was the opinion of Daines Barrington and White of
Selborne, who both especially attended to this subject.[87] Barrington,
however, admits that "superiority in song gives to birds an amazing
ascendancy over others, as is well known to bird-catchers."
It is certain that there is an intense degree of rivalry between the
males in their singing. Bird-fanciers match their birds to see which
will sing longest; and I was told by Mr. Yarrell that a first-rate bird
will sometimes sing till he drops down almost dead, or, according to
Bechstein,[88] quite dead from rupturing a vessel in the lungs. Whatever
the cause may be, male birds, as I hear from Mr. Weir, often die
suddenly during the season of song. That the habit of singing is
sometimes quite independent of love is clear, for a sterile hybrid
canary-bird has been described[89] as singing whilst viewing itself in a
mirror, and then dashing at its own image; it likewise attacked with
fury a female canary when put into the same cage. The jealousy excited
by the act of singing is constantly taken advantage of by bird-catchers;
a male, in good song, is hidden and protected, whilst a stuffed bird,
surrounded by limed twigs, is exposed to view. In this manner a man, as
Mr. Weir informs me, has caught, in the course of a single day, fifty,
and in one instance seventy, male chaffinches. The power and inclination
to sing differ so greatly with birds that although the price of an
ordinary male chaffinch is only sixpence, Mr. Weir saw one bird for
which the bird-catcher asked three pounds; the test of a really good
singer being that it will continue to sing whilst the cage is swung
round the owner's head.
That birds should sing from emulation as well as for the sake of
charming the female, is not at all incompatible; and, indeed, might have
been expected to go together, like decoration and pugnacity. Some
authors, however, argue that the song of the male cannot serve to charm
the female, because the females of some few species, such as the canary,
robin, lark, and bullfinch, especially, as Bechstein remarks, when in a
state of widowhood, pour forth fairly melodious strains. In some of
these cases the habit of singing may be in part attributed to the
females having been highly fed and confined,[90] for this disturbs all
the usual functions connected with the reproduction of the species. Many
instances have already been given of the partial transference of
secondary masculine characters to the female, so that it is not at all
surprising that the females of some species should possess the power of
song. It has also been argued, that the song of the male cannot serve as
a charm, because the males of certain species, for instance, of the
robin, sing during the autumn.[91] But nothing is more common than for
animals to take pleasure in practising whatever instinct they follow at
other times for some real good. How often do we see birds which fly
easily, gliding and sailing through the air obviously for pleasure. The
cat plays with the captured mouse, and the cormorant with the captured
fish. The weaver-bird (Ploceus), when confined in a cage, amuses itself
by neatly weaving blades of grass between the wires of its cage. Birds
which habitually fight during the breeding-season are generally ready to
fight at all times; and the males of the capercailzie sometimes hold
their _balzens_ or _leks_ at the usual place of assemblage during the
autumn.[92] Hence it is not at all surprising that male birds should
continue singing for their own amusement after the season for courtship
is over.
Singing is to a certain extent, as shewn in a previous chapter, an art,
and is much improved by practice. Birds can be taught various tunes, and
even the unmelodious sparrow has learnt to sing like a linnet. They
acquire the song of their foster-parents,[93] and sometimes that of
their neighbours.[94] All the common songsters belong to the Order of
Insessores, and their vocal organs are much more complex than those of
most other birds; yet it is a singular fact that some of the Insessores,
such as ravens, crows, and magpies, possess the proper apparatus,[95]
though they never sing, and do not naturally modulate their voices to
any great extent. Hunter asserts[96] that with the true songsters the
muscles of the larynx are stronger in the males than in the females; but
with this slight exception there is no difference in the vocal organs of
the two sexes, although the males of most species sing so much better
and more continuously than the females.
It is remarkable that only small birds properly sing. The Australian
genus Menura, however, must be excepted; for the _Menura Alberti_, which
is about the size of a half-grown turkey, not only mocks other birds,
but "its own whistle is exceedingly beautiful and varied." The males
congregate and form "_corroborying_ places," where they sing, raising
and spreading their tails like peacocks and drooping their wings.[97]
It is also remarkable that the birds which sing are rarely decorated
with brilliant colours or other ornaments. Of our British birds,
excepting the bullfinch and goldfinch, the best songsters are
plain-coloured. The kingfisher, bee-eater, roller, hoopoe, woodpeckers,
&c., utter harsh cries; and the brilliant birds of the tropics are
hardly ever songsters.[98] Hence bright colours and the power of song
seem to replace each other. We can perceive that if the plumage did not
vary in brightness, or if bright colours were dangerous to the species,
other means would have to be employed to charm the females; and the
voice being rendered melodious would offer one such means.
[Illustration: Fig. 39. Tetrao cupido; male. (From Brehm.)]
In some birds the vocal organs differ greatly in the two sexes. In the
_Tetrao cupido_ (fig. 39) the male has two bare, orange-coloured sacks,
one on each side of the neck; and these are largely inflated when the
male, during the breeding-season, makes a curious hollow sound, audible
at a great distance. Audubon proved that the sound was intimately
connected with this apparatus, which reminds us of the air-sacks on each
side of the mouth of certain male frogs, for he found that the sound was
much diminished when one of the sacks of a tame bird was pricked, and
when both were pricked it was altogether stopped. The female has "a
somewhat similar, though smaller, naked space of skin on the neck; but
this is not capable of inflation."[99] The male of another kind of
grouse (_Tetrao urophasianus_), whilst courting the female, has his
"bare yellow oesophagus inflated to a prodigious size, fully half as
large as the body;" and he then utters various grating, deep hollow
tones. With his neck-feathers erect, his wings lowered and buzzing on
the ground, and his long pointed tail spread out like a fan, he displays
a variety of grotesque attitudes. The oesophagus of the female is not
in any way remarkable.[100]
It seems now well made out that the great throat-pouch of the European
male bustard (_Otis tarda_), and of at least four other species, does
not serve, as was formerly supposed, to hold water, but is connected
with the utterance during the breeding-season of a peculiar sound
resembling "ock." The bird whilst uttering this sound throws himself
into the most extraordinary attitudes. It is a singular fact that with
the males of the same species the sack is not developed in all the
individuals.[101] A crow-like bird inhabiting South America
(_Cephalopterus ornatus_, fig. 40) is called the umbrella-bird, from its
immense top-knot, formed of bare white quills surmounted by dark-blue
plumes, which it can elevate into a great dome no less than five inches
in diameter, covering the whole head. This bird has on its neck a long,
thin, cylindrical, fleshy appendage, which is thickly clothed with
scale-like blue feathers. It probably serves in part as an ornament, but
likewise as a resounding apparatus, for Mr. Bates found that it is
connected "with an unusual development of the trachea and vocal organs."
It is dilated when the bird utters its singularly deep, loud, and
long-sustained fluty note. The head-crest and neck-appendage are
rudimentary in the female.[102]
[Illustration: Fig. 40. The Umbrella-bird or Cephalopterus ornatus
(male, from Brehm).]
The vocal organs of various web-footed and wading birds are
extraordinarily complex, and differ to a certain extent in the two
sexes. In some cases the trachea is convoluted, like a French horn, and
is deeply embedded in the sternum. In the wild swan (_Cygnus ferus_) it
is more deeply embedded in the adult male than in the female or young
male. In the male Merganser the enlarged portion of the trachea is
furnished with an additional pair of muscles.[103] But the meaning of
these differences between the sexes of many Anatidae is not at all
understood; for the male is not always the more vociferous; thus with
the common duck, the male hisses, whilst the female utters a loud
quack.[104] In both sexes of one of the cranes (_Grus virgo_) the
trachea penetrates the sternum, but presents "certain sexual
modifications." In the male of the black stork there is also a
well-marked sexual difference in the length and curvature of the
bronchi.[105] So that highly important structures have in these cases
been modified according to sex.
It is often difficult to conjecture whether the many strange cries and
notes, uttered by male birds during the breeding-season, serve as a
charm or merely as a call to the female. The soft cooing of the
turtle-dove and of many pigeons, it may be presumed, pleases the female.
When the female of the wild turkey utters her call in the morning, the
male answers by a different note from the gobbling noise which he makes,
when with erected feathers, rustling wings and distended wattles, he
puffs and struts before her.[106] The _spel_ of the black-cock certainly
serves as a call to the female, for it has been known to bring four or
five females from a distance to a male under confinement; but as the
black-cock continues his _spel_ for hours during successive days, and in
the case of the capercailzie "with an agony of passion," we are led to
suppose that the females which are already present are thus
charmed.[107] The voice of the common rook is known to alter during the
breeding-season, and is therefore in some way sexual.[108] But what
shall we say about the harsh screams of, for instance, some kinds of
macaws; have these birds as bad taste for musical sounds as they
apparently have for colour, judging by the inharmonious contrast of
their bright yellow and blue plumage? It is indeed possible that the
loud voices of many male birds may be the result, without any advantage
being thus gained, of the inherited effects of the continued use of
their vocal organs, when they are excited by the strong passions of
love, jealousy, and rage; but to this point we shall recur when we treat
of quadrupeds.
We have as yet spoken only of the voice, but the males of various birds
practise, during their courtship, what may be called instrumental music.
Peacocks and Birds of Paradise rattle their quills together, and the
vibratory movement apparently serves merely to make a noise, for it can
hardly add to the beauty of their plumage. Turkey-cocks scrape their
wings against the ground, and some kinds of grouse thus produce a
buzzing sound. Another North American grouse, the _Tetrao umbellus_,
when with his tail erect, his ruffs displayed, "he shows off his finery
to the females, who lie hid in the neighbourhood," drums rapidly with
his "lowered wings on the trunk of a fallen tree," or, according to
Audubon, against his own body; the sound thus produced is compared by
some to distant thunder, and by others to the quick roll of a drum. The
female never drums, "but flies directly to the place where the male is
thus engaged." In the Himalayas the male of the Kalij pheasant "often
makes a singular drumming noise with his wings, not unlike the sound
produced by shaking a stiff piece of cloth." On the west coast of Africa
the little black-weavers (Ploceus?) congregate in a small party on the
bushes round a small open space, and sing and glide through the air with
quivering wings, "which make a rapid whirring sound like a child's
rattle." One bird after another thus performs for hours together, but
only during the courting-season. At this same season the males of
certain nightjars (Caprimulgus) make a most strange noise with their
wings. The various species of woodpeckers strike a sonorous branch with
their beaks, with so rapid a vibratory movement that "the head appears
to be in two places at once." The sound thus produced is audible at a
considerable distance, but cannot be described; and I feel sure that its
cause would never be conjectured by any one who heard it for the first
time. As this jarring sound is made chiefly during the breeding-season,
it has been considered as a love-song; but it is perhaps more strictly a
love-call. The female, when driven from her nest, has been observed thus
to call her mate, who answered in the same manner and soon appeared.
Lastly the male Hoopoe (_Upupa epops_) combines vocal and instrumental
music; for during the breeding-season this bird, as Mr. Swinhoe saw,
first draws in air and then taps the end of its beak perpendicularly
down against a stone or the trunk of a tree, "when the breath being
forced down the tubular bill produces the correct sound." When the male
utters its cry without striking his beak the sound is quite
different.[109]
[Illustration: Fig. 41. Outer tail-feather of Scolopax gallinago (from
Proc. Zool. Soc. 1858).]
In the foregoing cases sounds are made by the aid of structures already
present and otherwise necessary; but in the following cases certain
feathers have been specially modified for the express purpose of
producing the sounds. The drumming, or bleating, or neighing, or
thundering noise, as expressed by different observers, which is made by
the common snipe (_Scolopax gallinago_) must have surprised every one
who has ever heard it. This bird, during the pairing-season, flies to
"perhaps a thousand feet in height," and after zig-zagging about for a
time descends in a curved line, with outspread tail and quivering
pinions, with surprising velocity to the earth. The sound is emitted
only during this rapid descent. No one was able to explain the cause,
until M. Meves observed that on each side of the tail the outer feathers
are peculiarly formed (fig. 41), having a stiff sabre-shaped shaft, with
the oblique barbs of unusual length, the outer webs being strongly
bound together.
He found that by blowing on these feathers, or by fastening them to a
long thin stick and waving them rapidly through the air, he could
exactly reproduce the drumming noise made by the living bird. Both sexes
are furnished with these feathers, but they are generally larger in the
male than in the female, and emit a deeper note. In some species, as in
_S. frenata_ (fig. 42), four feathers, and in _S. javensis_ (fig. 43),
no less than eight on each side of the tail are greatly modified.
Different tones are emitted by the feathers of the different species
when waved through the air; and the _Scolopax Wilsonii_ of the United
States makes a switching noise whilst descending rapidly to the
earth.[110]
[Illustration: Fig. 42. Outer tail-feather of Scolopax frenata.]
[Illustration: Fig. 43. Outer tail-feather of Scolopax javensis.]
In the male of the _Chamaepetes unicolor_ (a large gallinaceous bird of
America) the first primary wing-feather is arched towards the tip and is
much more attenuated than in the female. In an allied bird, the
_Penelope nigra_, Mr. Salvin observed a male, which, whilst it flew
downwards "with outstretched wings, gave forth a kind of crashing,
rushing noise," like the falling of a tree.[111] The male alone of one
of the Indian bustards _(Sypheotides auritus_) has its primary
wing-feathers greatly acuminated; and the male of an allied species is
known to make a humming noise whilst courting the female.[112] In a
widely different group of birds, namely the Humming-birds, the males
alone of certain kinds have either the shafts of their primary
wing-feathers broadly dilated, or the webs abruptly excised towards the
extremity. The male, for instance, of _Selasphorus platycercus_, when
adult, has the first primary wing-feather (fig. 44), excised in this
manner. Whilst flying from flower to flower he makes "a shrill, almost
whistling, noise;"[113] but it did not appear to Mr. Salvin that the
noise was intentionally made.
[Illustration: Fig. 44. Primary wing-feather of a Humming-bird, the
_Selasphorus platycercus_ (from a sketch by Mr. Salvin). Upper figure,
that of male; lower figure, corresponding feather of female.]
Lastly, in several species of a sub-genus of Pipra or Manakin, the males
have their _secondary_ wing-feathers modified, as described by Mr.
Sclater, in a still more remarkable manner. In the brilliantly-coloured
_P. deliciosa_ the first three secondaries are thick-stemmed and curved
towards the body; in the fourth and fifth (fig. 45, _a_) the change is
greater; and in the sixth and seventh (_b_, _c_) the shaft "is thickened
to an extraordinary degree, forming a solid horny lump." The barbs also
are greatly changed in shape, in comparison with the corresponding
feathers (_d_, _e_, _f_) in the female. Even the bones of the wing which
support these singular feathers in the male are said by Mr. Fraser to be
much thickened. These little birds make an extraordinary noise, the
first "sharp note being not unlike the crack of a whip."[114]
[Illustration: Fig. 45. Secondary wing-feathers of _Pipra
deliciosa_(from Mr. Sclater, in Proc, Zool. Soc. 1860). The three upper
feathers, _a_, _b_, _c_, from the male; the three lower corresponding
feathers, _d_, _e_, _f_, from the female.
_a._ and _d._ Fifth secondary wing-feather of male and female, upper
surface. _b_ and _e_. Sixth secondary, upper surface. _c_ and _f_.
Seventh secondary, lower surface.]
The diversity of the sounds, both vocal and instrumental, made by the
males of many species during the breeding-season, and the diversity of
the means for producing such sounds, are highly remarkable. We thus gain
a high idea of their importance for sexual purposes, and are reminded of
the same conclusion with respect to insects. It is not difficult to
imagine the steps by which the notes of a bird, primarily used as a mere
call or for some other purpose, might have been improved into a
melodious love-song. This is somewhat more difficult in the case of the
modified feathers, by which the drumming, whistling, or roaring noises
are produced. But we have seen that some birds during their courtship
flutter, shake, or rattle their unmodified feathers together; and if the
females were led to select the best performers, the males which
possessed the strongest or thickest, or most attenuated feathers,
situated on any part of the body, would be the most successful; and thus
by slow degrees the feathers might be modified to almost any extent. The
females, of course, would not notice each slight successive alteration
in shape, but only the sounds thus produced. It is a curious fact that
in the same class of animals, sounds so different as the drumming of the
snipe's tail, the tapping of the woodpecker's beak, the harsh
trumpet-like cry of certain water-fowl, the cooing of the turtle-dove,
and the song of the nightingale, should all be pleasing to the females
of the several species. But we must not judge the tastes of distinct
species by a uniform standard; nor must we judge by the standard of
man's taste. Even with man, we should remember what discordant noises,
the beating of tom-toms and the shrill notes of reeds, please the ears
of savages. Sir S. Baker remarks,[115] that "as the stomach of the Arab
prefers the raw meat and reeking liver taken hot from the animal, so
does his ear prefer his equally coarse and discordant music to all
other."
_Love-Antics and Dances._--The curious love-gestures of various birds,
especially of the Gallinaceae, have already been incidentally noticed; so
that little need here be added. In Northern America, large numbers of a
grouse, the _Tetrao phasianellus_, meet every morning during the
breeding-season on a selected level spot, and here they run round and
round in a circle of about fifteen or twenty feet in diameter, so that
the ground is worn quite bare, like a fairy-ring. In these
Partridge-dances, as they are called by the hunters, the birds assume
the strangest attitudes, and run round, some to the left and some to the
right. Audubon describes the males of a heron (_Ardea herodias_) as
walking about on their long legs with great dignity before the females,
bidding defiance to their rivals. With one of the disgusting
carrion-vultures (_Cathartes jota_) the same naturalist states that "the
gesticulations and parade of the males at the beginning of the
love-season are extremely ludicrous." Certain birds perform their
love-antics on the wing, as we have seen with the black African weaver,
instead of on the ground. During the spring our little white-throat
(_Sylvia cinerea_) often rises a few feet or yards in the air above some
bush, and "flutters with a fitful and fantastic motion, singing all the
while, and then drops to its perch." The great English bustard throws
himself into indescribably odd attitudes whilst courting the female, as
has been figured by Wolf. An allied Indian bustard (_Otis bengalensis_)
at such times "rises perpendicularly into the air with a hurried
flapping of his wings, raising his crest and puffing out the feathers of
his neck and breast, and then drops to the ground;" he repeats this
manoeuvre several times successively, at the same time humming in a
peculiar tone. Such females as happen to be near "obey this saltatory
summons," and when they approach he trails his wings and spreads his
tail like a turkey-cock.[116]
But the most curious case is afforded by three allied genera of
Australian birds, the famous Bower-birds,--no doubt the co-descendants
of some ancient species which first acquired the strange instinct of
constructing bowers for performing their love-antics. The bowers (fig.
46), which, as we shall hereafter see, are highly decorated with
feathers, shells, bones and leaves, are built on the ground for the sole
purpose of courtship, for their nests are formed in trees. Both sexes
assist in the erection of the bowers, but the male is the principal
workman. So strong is this instinct that it is practised under
confinement, and Mr. Strange has described[117] the habits of some Satin
Bower-birds, which he kept in his aviary in New South Wales. "At times
the male will chase the female all over the aviary, then go to the
bower, pick up a gay feather or a large leaf, utter a curious kind of
note, set all his feathers erect, run round the bower and become so
excited that his eyes appear ready to start from his head; he continues
opening first one wing, and then the other, uttering a low, whistling
note, and, like the domestic cock, seems to be picking up something
from the ground, until at last the female goes gently towards him."
Captain Stokes has described the habits and "play-houses" of another
species, the Great Bower-bird, which was seen "amusing itself by flying
backwards and forwards, taking a shell alternately from each side, and
carrying it through the archway in its mouth." These curious structures,
formed solely as halls of assemblages, where both sexes amuse themselves
and pay their court, must cost the birds much labour. The bower, for
instance, of the fawn-breasted species, is nearly four feet in length,
eighteen inches in height, and is raised on a thick platform of sticks.
[Illustration: Fig. 46. Bower-bird, Chlamydera maculata, with bower (from
Brehm).]
_Decoration._--I will first discuss the cases in which the males are
ornamented either exclusively or in a much higher degree than the
females; and in a succeeding chapter those in which both sexes are
equally ornamented, and finally the rare cases in which the female is
somewhat more brightly-coloured than the male. As with the artificial
ornaments used by savage and civilised men, so with the natural
ornaments of birds, the head is the chief seat of decoration.[118] The
ornaments, as mentioned at the commencement of this chapter, are
wonderfully diversified. The plumes on the front or back of the head
consist of variously-shaped feathers, sometimes capable of erection or
expansion, by which their beautiful colours are fully displayed. Elegant
ear-tufts (see fig. 39 ante) are occasionally present. The head is
sometimes covered with velvety down like that of the pheasant; or is
naked and vividly coloured; or supports fleshy appendages, filaments,
and solid protuberances. The throat, also, is sometimes ornamented with
a beard, or with wattles or caruncles. Such appendages are generally
brightly coloured, and no doubt serve as ornaments, though not always
ornamental in our eyes; for whilst the male is in the act of courting
the female, they often swell and assume more vivid tints, as in the case
of the male turkey. At such times the fleshy appendages about the head
of the male Tragopan pheasant (_Ceriornis temminckii_) swell into a
large lappet on the throat and into two horns, one on each side of the
splendid top-knot; and these are then coloured of the most intense blue
which I have ever beheld. The African hornbill (_Bucorax abyssinicus_)
inflates the scarlet bladder-like wattle on its neck, and with its wings
drooping and tail expanded "makes quite a grand appearance."[119] Even
the iris of the eye is sometimes more brightly coloured in the male than
in the female; and this is frequently the case with the beak, for
instance, in our common blackbird. In _Buceros corrugatus_, the whole
beak and immense casque are coloured more conspicuously in the male than
in the female; and "the oblique grooves upon the sides of the lower
mandible are peculiar to the male sex."[120]
The males are often ornamented with elongated feathers or plumes
springing from almost every part of the body. The feathers on the throat
and breast are sometimes developed into beautiful ruffs and collars. The
tail-feathers are frequently increased in length; as we see in the
tail-coverts of the peacock, and in the tail of the Argus pheasant. The
body of this latter bird is not larger than that of a fowl; yet the
length from the end of the beak to the extremity of the tail is no less
than five feet three inches.[121] The wing-feathers are not elongated
nearly so often as the tail-feathers; for their elongation would impede
the act of flight. Yet the beautifully ocellated secondary wing-feathers
of the male Argus pheasant are nearly three feet in length; and in a
small African nightjar (_Cosmetornis vexillarius_) one of the primary
wing-feathers, during the breeding-season, attains a length of
twenty-six inches, whilst the bird itself is only ten inches in length.
In another closely-allied genus of nightjars, the shafts of the
elongated wing-feathers are naked, except at the extremity, where there
is a disc.[122] Again, in another genus of nightjars, the tail-feathers
are even still more prodigiously developed; so that we see the same kind
of ornament gained by the males of closely-allied birds, through the
development of widely different feathers.
It is a curious fact that the feathers of birds belonging to distinct
groups have been modified in almost exactly the same peculiar manner.
Thus the wing-feathers in one of the above-mentioned nightjars are bare
along the shaft and terminate in a disc; or are, as they are sometimes
called, spoon or racket-shaped. Feathers of this kind occur in the tail
of a motmot (_Eumomota superciliaris_), of a kingfisher, finch,
humming-bird, parrot, several Indian drongos (_Dicrurus_ and _Edolius_,
in one of which the disc stands vertically), and in the tail of certain
Birds of Paradise. In these latter birds, similar feathers, beautifully
ocellated, ornament the head, as is likewise the case with some
gallinaceous birds. In an Indian bustard (_Sypheotides auritus_) the
feathers forming the ear-tufts, which are about four inches in length,
also terminate in discs.[123] The barbs of the feathers in various
widely-distinct birds are filamentous or plumose, as with some Herons,
Ibises, Birds of Paradise and Gallinaceae. In other cases the barbs
disappear, leaving the shafts bare; and these in the tail of the
_Paradisea apoda_ attain a length of thirty-four inches.[124] Smaller
feathers when thus denuded appear like bristles, as on the breast of the
turkey-cock. As any fleeting fashion in dress comes to be admired by
man, so with birds a change of almost any kind in the structure or
colouring of the feathers in the male appears to have been admired by
the female. The fact of the feathers in widely distinct groups, having
been modified in an analogous manner, no doubt depends primarily on all
the feathers having nearly the same structure and manner of development,
and consequently tending to vary in the same manner. We often see a
tendency to analogous variability in the plumage of our domestic breeds
belonging to distinct species. Thus top-knots have appeared in several
species. In an extinct variety of the turkey, the top-knot consisted of
bare quills surmounted with plumes of down, so that they resembled, to a
certain extent, the racket-shaped feathers above described. In certain
breeds of the pigeon and fowl the feathers are plumose, with some
tendency in the shafts to be naked. In the Sebastopol goose the scapular
feathers are greatly elongated, curled, or even spirally twisted, with
the margins plumose.[125]
[Illustration: Fig. 47. Paradisea rubra, male (from Brehm)]
[Illustration: Fig. 48. Lophornis ornatus, male and female (from
Brehm).]
In regard to colour hardly anything need here be said; for every one
knows how splendid are the tints of birds, and how harmoniously they
are combined. The colours are often metallic and iridescent. Circular
spots are sometimes surrounded by one or more differently shaded zones,
and are thus converted into ocelli. Nor need much be said on the
wonderful differences between the sexes, or of the extreme beauty of the
males of many birds. The common peacock offers a striking instance.
Female Birds of Paradise are obscurely coloured and destitute of all
ornaments, whilst the males are probably the most highly decorated of
all birds, and in so many ways, that they must be seen to be
appreciated. The elongated and golden-orange plumes which spring from
beneath the wings of the _Paradisea apoda_ (see fig. 47 of _P. rubra_, a
much less beautiful species), when vertically erected and made to
vibrate, are described as forming a sort of halo, in the centre of which
the head "looks like a little emerald sun with its rays formed by the
two plumes."[126] In another most beautiful species the head is bald,
"and of a rich cobalt blue, crossed by several lines of black velvety
feathers."[127]
[Illustration: Fig. 49. Spathura underwoodi, male and female (from
Brehm).]
Male humming-birds (figs. 48 and 49) almost vie with Birds of Paradise
in their beauty, as every one will admit who has seen Mr. Gould's
splendid volumes or his rich collection. It is very remarkable in how
many different ways these birds are ornamented. Almost every part of the
plumage has been taken advantage of and modified; and the modifications
have been carried, as Mr. Gould shewed me, to a wonderful extreme in
some species belonging to nearly every sub-group. Such cases are
curiously like those which we see in our fancy breeds, reared by man for
the sake of ornament: certain individuals originally varied in one
character, and other individuals belonging to the same species in other
characters; and these have been seized on by man and augmented to an
extreme point--as the tail of the fantail-pigeon, the hood of the
jacobin, the beak and wattle of the carrier, and so forth. The sole
difference between these cases is that in the one the result is due to
man's selection, whilst in the other, as with Humming-birds, Birds of
Paradise, &c., it is due to sexual selection,--that is to the selection
by the females of the more beautiful males.
I will mention only one other bird, remarkable from the extreme
contrast in colour between the sexes, namely the famous Bell-bird
(_Chasmorhynchus niveus_) of S. America, the note of which can be
distinguished at the distance of nearly three miles, and astonishes
every one who first hears it. The male is pure white, whilst the female
is dusky-green; and the former colour with terrestrial species of
moderate size and inoffensive habits is very rare. The male, also, as
described by Waterton, has a spiral tube, nearly three inches in length,
which rises from the base of the beak. It is jet-black, dotted over with
minute downy feathers. This tube can be inflated with air, through a
communication with the palate; and when not inflated hangs down on one
side. The genus consists of four species, the males of which are very
distinct, whilst the females, as described by Mr. Sclater in a most
interesting paper, closely resemble each other, thus offering an
excellent instance of the common rule that within the same group the
males differ much more from each other than do the females. In a second
species (_C. nudicollis_) the male is likewise snow-white, with the
exception of a large space of naked skin on the throat and round the
eyes, which during the breeding-season is of a fine green colour. In a
third species (_C. tricarunculatus_) the head and neck alone of the male
are white, the rest of the body being chesnut-brown, and the male of
this species is provided with three filamentous projections half as long
as the body--one rising from the base of the beak and the two others
from the corners of the mouth.[128]
The coloured plumage and certain other ornaments of the males when
adult are either retained for life or are periodically renewed during
the summer and breeding-season. At this season the beak and naked skin
about the head frequently change colour, as with some herons, ibises,
gulls, one of the bell-birds just noticed, &c. In the white ibis, the
cheeks, the inflatable skin of the throat, and the basal portion of the
beak, then become crimson.[129] In one of the rails, _Gallicrex
cristatus_ a large red caruncle is developed during this same period on
the head of the male. So it is with a thin horny crest on the beak of
one of the pelicans, _P. erythrorhynchus_; for after the
breeding-season, these horny crests are shed, like horns from the heads
of stags, and the shore of an island in a lake in Nevada was found
covered with these curious exuviae.[130]
Changes of colour in the plumage according to the season depend firstly
on a double annual moult, secondly on an actual change of colour in the
feathers themselves, and thirdly on their dull-coloured margins being
periodically shed, or on these three processes more or less combined.
The shedding of the deciduary margins may be compared with the shedding
by very young birds of their down; for the down in most cases arises
from the summits of the first true feathers.[131]
With respect to the birds which annually undergo a double moult, there
are, firstly, some kinds, for instance snipes, swallow-plovers
(Glareolae), and curlews, in which the two sexes resemble each other and
do not change colour at any season. I do not know whether the
winter-plumage is thicker and warmer than the summer-plumage, which
seems, when there is no change of colour, the most probable cause of a
double moult. Secondly, there are birds, for instance certain species of
Totanus and other grallatores, the sexes of which resemble each other,
but have a slightly different summer and winter plumage. The difference,
however, in colour in these cases is so slight that it can hardly be an
advantage to them; and it may, perhaps, be attributed to the direct
action of the different conditions to which the birds are exposed during
the two seasons. Thirdly, there are many other birds the sexes of which
are alike, but which are widely different in their summer and winter
plumage. Fourthly, there are birds, the sexes of which differ from each
other in colour; but the females, though moulting twice, retain the same
colours throughout the year, whilst the males undergo a change,
sometimes, as with certain bustards, a great change of colour. Fifthly
and lastly, there are birds the sexes of which differ from each other in
both their summer and winter plumage, but the male undergoes a greater
amount of change at each recurrent season than the female--of which the
Ruff (_Machetes pugnax_) offers a good instance.
With respect to the cause or purpose of the differences in colour
between the summer and winter plumage, this may in some instances, as
with the ptarmigan,[132] serve during both seasons as a protection. When
the difference between the two plumages is slight it may perhaps be
attributed, as already remarked, to the direct action of the conditions
of life. But with many birds there can hardly be a doubt that the summer
plumage is ornamental, even when both sexes are alike. We may conclude
that this is the case with many herons, egrets, &c., for they acquire
their beautiful plumes only during the breeding-season. Moreover, such
plumes, top-knots, &c., though possessed by both sexes, are occasionally
a little more highly developed in the male than in the female; and they
resemble the plumes and ornaments possessed by the males alone of other
birds. It is also known that confinement, by affecting the reproductive
system of male birds, frequently checks the development of their
secondary sexual characters, but has no immediate influence on any other
characters; and I am informed by Mr. Bartlett that eight or nine
specimens of the Knot (_Tringa canutus_) retained their unadorned winter
plumage in the Zoological Gardens throughout the year, from which fact
we may infer that the summer plumage though common to both sexes
partakes of the nature of the exclusively masculine plumage of many
other birds.[133]
From the foregoing facts, more especially from neither sex of certain
birds changing colour during either annual moult, or changing so
slightly that the change can hardly be of any service to them, and from
the females of other species moulting twice yet retaining the same
colours throughout the year, we may conclude that the habit of moulting
twice in the year has not been acquired in order that the male should
assume during the breeding-season an ornamental character; but that the
double moult, having been originally acquired for some distinct purpose,
has subsequently been taken advantage of in certain cases for gaining a
nuptial plumage.
It appears at first sight a surprising circumstance that with
closely-allied birds, some species should regularly undergo a double
annual moult, and others only a single one. The ptarmigan, for instance,
moults twice or even thrice in the year, and the black-cock only once:
some of the splendidly-coloured honey-suckers (Nectariniae) of India and
some sub-genera of obscurely-coloured pipits (Anthus) have a double,
whilst others have only a single annual moult.[134] But the gradations
in the manner of moulting, which are known to occur with various birds,
shew us how species, or whole groups of species, might have originally
acquired their double annual moult, or having once gained the habit,
have again lost it. With certain bustards and plovers the vernal moult
is far from complete, some feathers being renewed, and some changed in
colour. There is also reason to believe that with certain bustards and
rail-like birds, which properly undergo a double moult, some of the
older males retain their nuptial plumage throughout the year. A few
highly modified feathers may alone be added during the spring to the
plumage, as occurs with the disc-formed tail-feathers of certain drongos
(_Bhringa_) in India, and with the elongated feathers on the back, neck,
and crest of certain herons. By such steps as these, the vernal moult
might be rendered more and more complete, until a perfect double moult
was acquired. A gradation can also be shewn to exist in the length of
time during which either annual plumage is retained; so that the one
might come to be retained for the whole year, the other being completely
lost. Thus the _Machetes pugnax_ retains his ruff in the spring for
barely two months. The male widow-bird (_Chera progne_) acquires in
Natal his fine plumage and long tail-feathers in December or January and
loses them in March; so that they are retained during only about three
months. Most species which undergo a double moult keep their ornamental
feathers for about six months. The male, however, of the wild _Gallus
bankiva_ retains his neck-hackles for nine or ten months; and when these
are cast off, the underlying black feathers on the neck are fully
exposed to view. But with the domesticated descendant of this species,
the neck-hackles of the male are immediately replaced by new ones; so
that we here see, with respect to part of the plumage, a double moult
changed under domestication into a single moult.[135]
The common drake (_Anas boschas_) is well known after the
breeding-season to lose his male plumage for a period of three months,
during which time he assumes that of the female. The male pintail-duck
(_Anas acuta_) loses his plumage for the shorter period of six weeks or
two months; and Montagu remarks that "this double moult within so short
a time is a most extraordinary circumstance, that seems to bid defiance
to all human reasoning." But he who believes in the gradual modification
of species will be far from feeling surprise at finding gradations of
all kinds. If the male pintail were to acquire his new plumage within a
still shorter period, the new male feathers would almost necessarily be
mingled with the old, and both with some proper to the female; and this
apparently is the case with the male of a not distantly-allied bird,
namely the _Merganser serrator_, for the males are said to "undergo a
change of plumage, which assimilates them in some measure to the
female." By a little further acceleration in the process, the double
moult would be completely lost.[136]
Some male birds, as before stated, become more brightly coloured in the
spring, not by a vernal moult, but either by an actual change of colour
in the feathers, or by their obscurely-coloured deciduary margins being
shed. Changes of colour thus caused may last for a longer or shorter
time. With the _Pelecanus onocrotalus_ a beautiful rosy tint, with
lemon-coloured marks on the breast, overspreads the whole plumage in the
spring; but these tints, as Mr. Sclater states, "do not last long,
disappearing generally in about six weeks or two months after they have
been attained." Certain finches shed the margins of their feathers in
the spring, and then become brighter-coloured, while other finches
undergo no such change. Thus the _Fringilla tristis_ of the United
States (as well as many other American species), exhibits its bright
colours only when the winter is past, whilst our goldfinch, which
exactly represents this bird in habits, and our siskin, which
represents it still more closely in structure, undergo no such annual
change. But a difference of this kind in the plumage of allied species
is not surprising, for with the common linnet, which belongs to the same
family, the crimson forehead and breast are displayed only during the
summer in England, whilst in Madeira these colours are retained
throughout the year.[137]
_Display by Male Birds of their Plumage._--Ornaments of all kinds,
whether permanently or temporarily gained, are sedulously displayed by
the males, and apparently serve to excite, or attract, or charm the
females. But the males will sometimes display their ornaments, when not
in the presence of the females, as occasionally occurs with grouse at
their balz-places, and as may be noticed with the peacock; this latter
bird, however, evidently wishes for a spectator of some kind, and will
shew off his finery, as I have often seen, before poultry or even
pigs.[138] All naturalists who have closely attended to the habits of
birds, whether in a state of nature or under confinement, are
unanimously of opinion that the males delight to display their beauty.
Audubon frequently speaks of the male as endeavouring in various ways to
charm the female. Mr. Gould, after describing some peculiarities in a
male humming-bird, says he has no doubt that it has the power of
displaying them to the greatest advantage before the female. Dr.
Jerdon[139] insists that the beautiful plumage of the male serves "to
fascinate and attract the female." Mr. Bartlett, at the Zoological
Gardens, expressed himself to me in the strongest terms to the same
effect.
It must be a grand sight in the forests of India "to come suddenly on
twenty or thirty peafowl, the males displaying their gorgeous trains,
and strutting about in all the pomp of pride before the gratified
females." The wild turkey-cock erects his glittering plumage, expands
his finely-zoned tail and barred wing-feathers, and altogether, with his
gorged crimson and blue wattles, makes a superb, though, to our eyes,
grotesque appearance. Similar facts have already been given with respect
to grouse of various kinds. Turning to another Order. The male _Rupicola
crocea_ (fig. 50) is one of the most beautiful birds in the world, being
of a splendid orange, with some of the feathers curiously truncated and
plumose. The female is brownish-green, shaded with red, and has a much
smaller crest. Sir R. Schomburgk has described their courtship; he found
one of their meeting-places where ten males and two females were
present. The space was from four to five feet in diameter, and appeared
to have been cleared of every blade of grass and smoothed as if by human
hands. A male "was capering to the apparent delight of several others.
Now spreading its wings, throwing up its head, or opening its tail like
a fan; now strutting about with a hopping gait until tired, when it
gabbled some kind of note, and was relieved by another. Thus three of
them successively took the field, and then, with self-approbation,
withdrew to rest." The Indians, in order to obtain their skins, wait at
one of the meeting-places till the birds are eagerly engaged in dancing,
and then are able to kill, with their poisoned arrows, four or five
males, one after the other.[140] With Birds of Paradise a dozen or more
full-plumaged males congregate in a tree to hold a dancing-party, as it
is called by the natives; and here flying about, raising their wings,
elevating their exquisite plumes, and making them vibrate, the whole
tree seems, as Mr. Wallace remarks, to be filled with waving plumes.
When thus engaged, they become so absorbed that a skilful archer may
shoot nearly the whole party. These birds, when kept in confinement in
the Malay Archipelago, are said to take much care in keeping their
feathers clean; often spreading them out, examining them, and removing
every speck of dirt. One observer, who kept several pairs alive, did not
doubt that the display of the male was intended to please the
female.[141]
[Illustration: Fig. 50. Rupicola crocea, male (from Brehm).]
The gold pheasant (_Thaumalea picta_) during his courtship not only
expands and raises his splendid frill, but turns it, as I have myself
seen, obliquely towards the female on whichever side she may be
standing, obviously in order that a large surface may be displayed
before her.[142] Mr. Bartlett has observed a male Polyplectron (fig. 51)
in the act of courtship, and has shewn me a specimen stuffed in the
attitude then assumed. The tail and wing-feathers of this bird are
ornamented with beautiful ocelli, like those on the peacock's train. Now
when the peacock displays himself, he expands and erects his tail
transversely to his body, for he stands in front of the female, and has
to shew off, at the same time, his rich blue throat and breast. But the
breast of the Polyplectron is obscurely coloured, and the ocelli are not
confined to the tail-feathers. Consequently the Polyplectron does not
stand in front of the female; but he erects and expands his
tail-feathers a little obliquely, lowering the expanded wing on the
same side, and raising that on the opposite side. In this attitude the
ocelli over the whole body are exposed before the eyes of the admiring
female in one grand bespangled expanse. To whichever side she may turn,
the expanded wings and the obliquely-held tail are turned towards her.
The male Tragopan pheasant acts in nearly the same manner, for he raises
the feathers of the body, though not the wing itself, on the side which
is opposite to the female, and which would otherwise be concealed, so
that nearly all the beautifully-spotted feathers are exhibited at the
same time.
[Illustration: Fig. 51. Polyplectron chinquis, male (from Brehm)]
The case of the Argus pheasant is still more striking. The immensely
developed secondary wing-feathers, which are confined to the male, are
ornamented with a row of from twenty to twenty-three ocelli, each above
an inch in diameter. The feathers are also elegantly marked with oblique
dark stripes and rows of spots, like those on the skin of a tiger and
leopard combined. The ocelli are so beautifully shaded that, as the Duke
of Argyll remarks,[143] they stand out like a ball lying loosely within
a socket. But when I looked at the specimen in the British Museum, which
is mounted with the wings expanded and trailing downwards, I was greatly
disappointed, for the ocelli appeared flat or even concave. Mr. Gould,
however, soon made the case clear to me, for he had made a drawing of a
male whilst he was displaying himself. At such times the long secondary
feathers in both wings are vertically erected and expanded; and these,
together with the enormously elongated tail-feathers, make a grand
semicircular upright fan. Now as soon as the wing-feathers are held in
this position, and the light shines on them from above, the full effect
of the shading comes out, and each ocellus at once resembles the
ornament called a ball and socket. These feathers have been shewn to
several artists, and all have expressed their admiration at the perfect
shading.
It may well be asked, could such artistically-shaded ornaments have been
formed by means of sexual selection? But it will be convenient to defer
giving an answer to this question until we treat in the next chapter of
the principle of gradation.
The primary wing-feathers, which in most gallinaceous birds are
uniformly coloured, are in the Argus pheasant not less wonderful objects
than the secondary wing-feathers. They are of a soft brown tint with
numerous dark spots, each of which consists of two or three black dots
with a surrounding dark zone. But the chief ornament is a space parallel
to the dark-blue shaft, which in outline forms a perfect second feather
lying within the true feather. This inner part is coloured of a lighter
chesnut, and is thickly dotted with minute white points. I have shewn
this feather to several persons, and many have admired it even more than
the ball-and-socket feathers, and have declared that it was more like a
work of art than of nature. Now these feathers are quite hidden on all
ordinary occasions, but are fully displayed when the long secondary
feathers are erected, though in a widely different manner; for they are
expanded in front like two little fans or shields, one on each side of
the breast near the ground.
The case of the male Argus pheasant is eminently interesting, because it
affords good evidence that the most refined beauty may serve as a charm
for the female, and for no other purpose. We must conclude that this is
the case, as the primary wing-feathers are never displayed, and the
ball-and-socket ornaments are not exhibited in full perfection, except
when the male assumes the attitude of courtship. The Argus pheasant does
not possess brilliant colours, so that his success in courtship appears
to have depended on the great size of his plumes, and on the
elaboration of the most elegant patterns. Many will declare that it is
utterly incredible that a female bird should be able to appreciate fine
shading and exquisite patterns. It is undoubtedly a marvellous fact that
she should possess this almost human degree of taste, though perhaps she
admires the general effect rather than each separate detail. He who
thinks that he can safely gauge the discrimination and taste of the
lower animals, may deny that the female Argus pheasant can appreciate
such refined beauty; but he will then be compelled to admit that the
extraordinary attitudes assumed by the male during the act of courtship,
by which the wonderful beauty of his plumage is fully displayed, are
purposeless; and this is a conclusion which I for one will never admit.
Although so many pheasants and allied gallinaceous birds carefully
display their beautiful plumage before the females, it is remarkable, as
Mr. Bartlett informs me, that this is not the case with the
dull-coloured Eared and Cheer pheasants (_Crossoptilon auritum_ and
_Phasianus Wallichii_); so that these birds seem conscious that they
have little beauty to display. Mr. Bartlett has never seen the males of
either of these species fighting together, though he has not had such
good opportunities for observing the Cheer as the Eared pheasant. Mr.
Jenner Weir, also, finds that all male birds with rich or
strongly-characterised plumage are more quarrelsome than the
dull-coloured species belonging to the same groups. The goldfinch, for
instance, is far more pugnacious than the linnet, and the blackbird
than the thrush. Those birds which undergo a seasonal change of plumage
likewise become much more pugnacious at the period when they are most
gaily ornamented. No doubt the males of some obscurely-coloured birds
fight desperately together, but it appears that when sexual selection
has been highly influential, and has given bright colours to the males
of any species, it has also very often given a strong tendency to
pugnacity. We shall meet with nearly analogous cases when we treat of
mammals. On the other hand, with birds the power of song and brilliant
colours have rarely been both acquired by the males of the same species;
but in this case, the advantage gained would have been identically the
same, namely success in charming the female. Nevertheless it must be
owned that the males of several brilliantly-coloured birds have had
their feathers specially modified for the sake of producing instrumental
music, though the beauty of this cannot be compared, at least according
to our taste, with that of the vocal music of many songsters.
We will now turn to male birds which are not ornamented in any very high
degree, but which nevertheless display, during their courtship, whatever
attractions they may possess. These cases are in some respects more
curious than the foregoing, and have been but little noticed. I owe the
following facts, selected from a large body of valuable notes, sent to
me by Mr. Jenner Weir, who has long kept birds of many kinds, including
all the British Fringillidae and Emberizidae. The bullfinch makes his
advances in front of the female, and then puffs out his breast, so that
many more of the crimson feathers are seen at once than otherwise would
be the case. At the same time he twists and bows his black tail from
side to side in a ludicrous manner. The male chaffinch also stands in
front of the female, thus shewing his red breast, and "blue bell," as
the fanciers call his head; the wings at the same time being slightly
expanded, with the pure white bands on the shoulders thus rendered
conspicuous. The common linnet distends his rosy breast, slightly
expands his brown wings and tail, so as to make the best of them by
exhibiting their white edgings. We must, however, be cautious in
concluding that the wings are spread out solely for display, as some
birds act thus whose wings are not beautiful. This is the case with the
domestic cock, but it is always the wing on the side opposite to the
female which is expanded, and at the same time scraped on the ground.
The male goldfinch behaves differently from all other finches: his wings
are beautiful, the shoulders being black, with the dark-tipped
wing-feathers spotted with white and edged with golden yellow. When he
courts the female, he sways his body from side to side, and quickly
turns his slightly expanded wings first to one side then to the other,
with a golden flashing effect. No other British finch, as Mr. Weir
informs me, turns during his courtship from side to side in this manner;
not even the closely-allied male siskin, for he would not thus add to
his beauty.
Most of the British Buntings are plain-coloured birds; but in the spring
the feathers on the head of the male reed-bunting (_Emberiza
schoeniculus_) acquire a fine black colour by the abrasion of the
dusky tips; and these are erected during the act of courtship. Mr. Weir
has kept two species of Amadina from Australia: the _A. castanotis_ is a
very small and chastely-coloured finch, with a dark tail, white rump,
and jet-black upper tail-coverts, each of the latter being marked with
three large conspicuous oval spots of white.[144] This species, when
courting the female, slightly spreads out and vibrates these
parti-coloured tail-coverts in a very peculiar manner. The male _Amadina
Lathami_ behaves very differently, exhibiting before the female his
brilliantly-spotted breast and scarlet rump and scarlet upper
tail-coverts. I may here add from Dr. Jerdon, that the Indian Bulbul
(_Pycnonotus haemorrhous_) has crimson _under_ tail-coverts, and the
beauty of these feathers, it might be thought, could never be well
exhibited; but the bird "when excited often spreads them out laterally,
so that they can be seen even from above."[145] The common pigeon has
iridescent feathers on the breast, and every one must have seen how the
male inflates his breast whilst courting the female, thus showing off
these feathers to the best advantage. One of the beautiful bronze-winged
pigeons of Australia (_Ocyphaps lophotes_) behaves, as described to me
by Mr. Weir, very differently: the male, whilst standing before the
female, lowers his head almost to the ground, spreads out and raises
perpendicularly his tail, and half expands his wings. He then
alternately and slowly raises and depresses his body, so that the
iridescent metallic feathers are all seen at once, and glitter in the
sun.
Sufficient facts have now been given to shew with what care male birds
display their various charms, and this they do with the utmost skill.
Whilst preening their feathers, they have frequent opportunities for
admiring themselves and of studying how best to exhibit their beauty.
But as all the males of the same species display themselves in exactly
the same manner, it appears that actions, at first perhaps intentional,
have become instinctive. If so, we ought not to accuse birds of
conscious vanity; yet when we see a peacock strutting about, with
expanded and quivering tail-feathers, he seems the very emblem of pride
and vanity.
The various ornaments possessed by the males are certainly of the
highest importance to them, for they have been acquired in some cases at
the expense of greatly impeded powers of flight or of running. The
African nightjar (_Cosmetornis_), which during the pairing-season has
one of its primary wing-feathers developed into a streamer of extreme
length, is thus much retarded in its flight, although at other times
remarkable for its swiftness. The "unwieldy size" of the secondary
wing-feathers of the male Argus pheasant are said "almost entirely to
deprive the bird of flight." The fine plumes of male Birds of Paradise
trouble them during a high wind. The extremely long tail-feathers of the
male widow-birds (Vidua) of Southern Africa render "their flight heavy;"
but as soon as these are cast off they fly as well as the females. As
birds always breed when food is abundant, the males probably do not
suffer much inconvenience in searching for food from their impeded
powers of movement; but there can hardly be a doubt that they must be
much more liable to be struck down by birds of prey. Nor can we doubt
that the long train of the peacock and the long tail and wing-feathers
of the Argus pheasant must render them a more easy prey to any prowling
tiger-cat than would otherwise be the case. Even the bright colours of
many male birds cannot fail to make them conspicuous to their enemies of
all kinds. Hence it probably is, as Mr. Gould has remarked, that such
birds are generally of a shy disposition, as if conscious that their
beauty was a source of danger, and are much more difficult to discover
or approach, than the sombre-coloured and comparatively tame females, or
than the young and as yet unadorned males.[146]
It is a more curious fact that the males of some birds which are
provided with special weapons for battle, and which in a state of nature
are so pugnacious that they often kill each other, suffer from
possessing certain ornaments. Cock-fighters trim the hackles and cut off
the comb and gills of their cocks; and the birds are then said to be
dubbed. An undubbed bird, as Mr. Tegetmeier insists, "is at a fearful
disadvantage: the comb and gills offer an easy hold to his adversary's
beak, and as a cock always strikes where he holds, when once he has
seized his foe, he has him entirely in his power. Even supposing that
the bird is not killed, the loss of blood suffered by an undubbed cock
is much greater than that sustained by one that has been trimmed."[147]
Young turkey-cocks in fighting always seize hold of each other's
wattles; and I presume that the old birds fight in the same manner. It
may perhaps be objected that the comb and wattles are not ornamental,
and cannot be of service to the birds in this way; but even to our eyes,
the beauty of the glossy black Spanish cock is much enhanced by his
white face and crimson comb; and no one who has ever seen the splendid
blue wattles of the male Tragopan pheasant, when distended during the
act of courtship, can for a moment doubt that beauty is the object
gained. From the foregoing facts we clearly see that the plumes and
other ornaments of the male must be of the highest importance to him;
and we further see that beauty in some cases is even more important than
success in battle.
CHAPTER XIV.
BIRDS--_continued_.
Choice exerted by the female--Length of courtship--Unpaired
birds--Mental qualities and taste for the
beautiful--Preference or antipathy shewn by the female for
particular males--Variability of birds--Variations sometimes
abrupt--Laws of variation--Formation of ocelli--Gradations of
character--Case of Peacock, Argus pheasant, and Urosticte.
When the sexes differ in beauty, in the power of singing, or in
producing what I have called instrumental music, it is almost invariably
the male which excels the female. These qualities, as we have just seen,
are evidently of high importance to the male. When they are gained for
only a part of the year, this is always shortly before the
breeding-season. It is the male alone who elaborately displays his
varied attractions, and often performs strange antics on the ground or
in the air, in the presence of the female. Each male drives away or, if
he can, kills all his rivals. Hence we may conclude, that it is the
object of the male to induce the female to pair with him, and for this
purpose he tries to excite or charm her in various ways; and this is the
opinion of all those who have carefully studied the habits of living
birds. But there remains a question which has an all important bearing
on sexual selection, namely, does every male of the same species equally
excite and attract the female? or does she exert a choice, and prefer
certain males? This question can be answered in the affirmative by much
direct and indirect evidence. It is much more difficult to decide what
qualities determine the choice of the females; but here again we have
some direct and indirect evidence that it is to a large extent the
external attractions of the male, though no doubt his vigour, courage,
and other mental qualities come into play. We will begin with the
indirect evidence.
_Length of Courtship._--The lengthened period during which both sexes of
certain birds meet day after day at an appointed place, probably depends
partly on the courtship being a prolonged affair, and partly on the
reiteration of the act of pairing. Thus in Germany and Scandinavia the
balzens or leks of the Black-cocks, last from the middle of March, all
through April into May. As many as forty or fifty, or even more birds
congregate at the leks; and the same place is often frequented during
successive years. The lek of the Capercailzie lasts from the end of
March to the middle or even end of May. In North America "the partridge
dances" of the _Tetrao phasianellus_ "last for a month or more." Other
kinds of grouse both in North America and Eastern Siberia[148] follow
nearly the same habits. The fowlers discover the hillocks where the
Ruffs congregate by the grass being trampled bare, and this shews that
the same spot is long frequented. The Indians of Guiana are well
acquainted with the cleared arenas, where they expect to find the
beautiful Cocks of the Rock; and the natives of New Guinea know the
trees where from ten to twenty full-plumaged male Birds of
Paradise congregate. In this latter case it is not expressly stated that
the females meet on the same trees, but the hunters, if not specially
asked, would not probably mention their presence, as their skins are
valueless. Small parties of an African weaver (_Ploceus_) congregate,
during the breeding-season, and perform for hours their graceful
evolutions. Large numbers of the Solitary snipe (_Scolopax major_)
assemble during the dusk in a morass; and the same place is frequented
for the same purpose during successive years; here they may be seen
running about "like so many large rats," puffing out their feathers,
flapping their wings, and uttering the strangest cries.[149]
Some of the above-mentioned birds, namely, the black-cock, capercailzie,
pheasant-grouse, the ruff, the Solitary snipe, and perhaps some others,
are, as it is believed, polygamists. With such birds it might have been
thought that the stronger males would simply have driven away the
weaker, and then at once have taken possession of as many females as
possible; but if it be indispensable for the male to excite or please
the female, we can understand the length of the courtship and the
congregation of so many individuals of both sexes at the same spot.
Certain species which are strictly monogamous likewise hold nuptial
assemblages; this seems to be the case in Scandinavia with one of the
ptarmigans, and their leks last from the middle of March to the middle
of May. In Australia the lyre-bird or _Menura superba_ forms "small
round hillocks," and the _M. Alberti_ scratches for itself shallow
holes, or, as they are called by the natives, _corroborying places_,
where it is believed both sexes assemble. The meetings of the _M.
superba_ are sometimes very large; and an account has lately been
published[150] by a traveller, who heard in a valley beneath him,
thickly covered with scrub, "a din which completely astonished" him; on
crawling onwards he beheld to his amazement about one hundred and fifty
of the magnificent lyre-cocks, "ranged in order of battle, and fighting
with indescribable fury." The bowers of the Bower-birds are the resort
of both sexes during the breeding-season; and "here the males meet and
contend with each other for the favours of the female, and here the
latter assemble and coquet with the males." With two of the genera, the
same bower is resorted to during many years.[151]
The common magpie (_Corvus pica_, Linn.), as I have been informed by the
Rev. W. Darwin Fox, used to assemble from all parts of Delamere Forest,
in order to celebrate the "great magpie marriage." Some years ago these
birds abounded in extraordinary numbers, so that a gamekeeper killed in
one morning nineteen males, and another killed by a single shot seven
birds at roost together. Whilst they were so numerous, they had the
habit very early in the spring of assembling at particular spots, where
they could be seen in flocks, chattering, sometimes fighting, bustling
and flying about the trees. The whole affair was evidently considered by
the birds as of the highest importance. Shortly after the meeting they
all separated, and were then observed by Mr. Fox and others to be
paired for the season. In any district in which a species does not exist
in large numbers, great assemblages cannot, of course, be held, and the
same species may have different habits in different countries. For
instance, I have never met with any account of regular assemblages of
black game in Scotland, yet these assemblages are so well known in
Germany and Scandinavia that they have special names.
_Unpaired Birds._--From the facts now given, we may conclude that with
birds belonging to widely-different groups their courtship is often a
prolonged, delicate, and troublesome affair. There is even reason to
suspect, improbable as this will at first appear, that some males and
females of the same species, inhabiting the same district, do not always
please each other and in consequence do not pair. Many accounts have
been published of either the male or female of a pair having been shot,
and quickly replaced by another. This has been observed more frequently
with the magpie than with any other bird, owing perhaps to its
conspicuous appearance and nest. The illustrious Jenner states that in
Wiltshire one of a pair was daily shot no less than seven times
successively, "but all to no purpose, for the remaining magpie soon
found another mate;" and the last pair reared their young. A new partner
is generally found on the succeeding day; but Mr. Thompson gives the
case of one being replaced on the evening of the same day. Even after
the eggs are hatched, if one of the old birds is destroyed a mate will
often be found; this occurred after an interval of two days, in a case
recently observed by one of Sir J. Lubbock's keepers.[152] The first and
most obvious conjecture is that male magpies must be much more numerous
than the females; and that in the above cases, as well in many others
which could be given, the males alone had been killed. This apparently
holds good in some instances, for the gamekeepers in Delamere Forest
assured Mr. Fox that the magpies and carrion-crows which they formerly
killed in succession in large numbers near their nests were all males;
and they accounted for this fact by the males being easily killed whilst
bringing food to the sitting females. Macgillivray, however, gives, on
the authority of an excellent observer, an instance of three magpies
successively killed on the same nest which were all females; and another
case of six magpies successively killed whilst sitting on the same eggs,
which renders it probable that most of them were females, though the
male will sit on the eggs, as I hear from Mr. Fox, when the female is
killed.