COURTSHIP AMONG BIRDS
Generalities—Darwin v. Wallace—The Peacock in his Pride—The “Display”
of the Peacock Pheasant—The Splendour of the Argus Pheasant and the
Marvel of its Eyes—The Frill of the Amherst Pheasant—Birds of Paradise
in the Toils of Love—Inflated Suitors—Ruffs and Reeves—Fearsome Weapons
and their Uses—Birds which dance—Musical Birds—The Bird’s Voice-box—The
“Lek” of the Capercaillie—Instruments of Percussion—The Curious
Performance of the Wood-pecker.
The fact that so little is known about the mammals during that period
when the all-important work of securing mates is going on, and of the
subsequent events, is largely due to the difficulties which close
observation of this phase of their life-history entails. With the birds
matters are far otherwise; their haunts are more accessible; they
are far more numerous, and much more easily kept under observation.
Consequently, we have a tolerably complete knowledge of the lives
of some species, at any rate, during the reproductive period; that
is to say, as to the sequence of events from the beginning of the
reproductive activities onwards; but the interpretation of what is seen
is another matter. No attempt which has yet been made to fathom the
psychology of sex has yielded more than a slight insight into what is
taking place. Nevertheless, this is an aspect of the subject which
has a far more important bearing on the problems of evolution than
is generally realized. But these pages are concerned rather with the
relations between the sexes, than with the subtle forces which have
fashioned and control conduct in this regard.
In all that concerns the problems of sex, which is to say of
reproduction, birds, speaking generally, display a briefer and more
condensed sequence of events than the mammals; and, moreover, many
species compel the attention even of the most incurious, to their
behaviour at this time, through the development, either of song, or
of fantastic displays of their amorous feelings: while others force
themselves no less conspicuously under notice by their habit of nesting
in large, and often enormous colonies.
In the matter of the development of secondary sexual characters birds
stand conspicuous among the Vertebrates, and easily eclipse the
mammals; among which bright, strongly contrasted, colours are the
exception. Among the birds they may almost be said to be the rule.
Also, in this category we have to reckon song, and the production of
more or less musical sounds by the agency of internal resonators or of
specially modified feathers; as well as quaint forms of posturing which
may be included under the head of dances. Further, some species have
developed formidable weapons of offence. These things are interesting
enough in themselves, but they become still more so when we reflect
that they formed the corner-stone of Darwin’s theory of “Sexual
Selection,” and that Wallace’s criticisms thereof were inspired by
evidence from the same source.
The interests of this chapter will best be served if the evidence
on which this theory was founded be first surveyed: when Darwin’s
deductions and the criticism which they have aroused will be the more
readily appreciated.
Definitions are always liable to exceptions; and concrete cases are
better than abstract terms. Birds, then, perhaps better than any
other group, illustrate what is meant by the term “secondary sexual
characters,” if only because examples are so constantly at hand. Save
among experts, sex among birds cannot be determined except by the
differences in plumage, or sometimes in size, which the sexes display.
But even here, it is only among species which occupy what we may call a
mid-evolutionary phase in which this discrimination is possible. Among
“generalized” species, wherein the plumage is of sombre hue, there is
no external distinguishing mark between male and female; and the same
is true with species which have attained to the maximum of resplendent
plumage; as for example many Parrots and Kingfishers, where again both
sexes, and at all ages, display the same vivid hues. Thus, in the
case of either of the two extremes, the study of behaviour during the
breeding season is one of great difficulty and no less uncertainty.
Where the sexes are sharply distinguished by differences of coloration,
however, as with the Peacock, the matter is otherwise. This bird, from
time immemorial the symbol of vanity, illustrates in a singularly
effective manner the broad features of what is commonly meant by
“courtship” among birds, while it furnishes a no less striking example
of the development of “secondary sexual characters.”
One might have supposed that birds, under the spell of that
irresistible desire for sexual intercourse, would behave differently in
regard to their “courtship” according to whether they were monogamous,
polygamous, or polyandrous: but while their behaviour during this
period of the life-history presents an extraordinary variety, it is
only at any rate slightly determined by the plurality or otherwise of
mates; and the same rule holds in regard to the brilliancy or otherwise
of coloration.
The most common manifestation of sexual desire among birds takes the
form of strange posturings which are, in some species, enormously
exaggerated by the display of vividly coloured frills, tufts, or other
conspicuous modifications of the normal plumage. The Peacock affords
a most excellent example of this combination of the contortionist and
the beau, though the nature of this display is by no means generally
understood. This applies more particularly to artists, who from time
immemorial to the present day, in essaying to paint the Peacock in his
pride, have invariably fallen into the error of treating the great
ocellated train as if it were the tail, placing it where, of course,
the tail ought to be, at the end of the body! As a matter of fact it
is nothing of the kind; these gorgeous plumes are really exaggerated
tail-coverts which, when set on end, appear to arise from an oval
shield of metallic green scales—the central back-feathers. When this
trailing glory is erected, the bird throws the body forwards and
downwards, so that the outermost train-feathers fall downwards on
either side in front of the wings, which are more or less trailed: so
that from the front only the head and neck are visible, the rest of the
body being hidden _behind_ the screen, as may be seen by a reference to
the accompanying photographs. The manner of this display is extremely
interesting, for the bird seems to be conscious of the effect produced:
though it cannot be supposed that this is really the case.
When displaying, the bird gradually approaches the nearest female
and slowly erects these extraordinary plumes. So soon as this is
accomplished he begins to walk backwards towards the object of his
attentions, presenting nothing but a great round shield of dull brown
feathers, backed up by the tail-feathers, and the dull-coloured wings.
So soon as he judges himself near enough, however, he suddenly swirls
round, confronting her in all his splendour, and heightening the effect
with a loud scream accompanied by a rapid, vibratory, motion of the
train-feathers which produces sounds like the pattering of rain on
leaves. Then he stands before her, with bowed head, as if to give her
an opportunity of drinking in his splendour to the full. Commonly,
however, she appears to be utterly indifferent, and either walks away
or continues a real, or affected hunt for food, as if no such thing as
a love-sick suitor were within a hundred miles of her! But sooner or
later his suggestive attitudes beget an answering response, and pairing
takes place.
The display of the beautiful Peacock Pheasant differs conspicuously
from that of the Peacock, and recalls that of the Argus Pheasant. In
the Peacock Pheasant, as will be seen from the adjoining photograph,
the wings, and tail, are alike bedecked with ocelli. The display is
made by the bird as it crouches close to the ground, with the wings and
tail raised to form a continuous, patterned surface, the head being
swiftly moved during the performance; hence its blurred outline in the
photograph.
[Illustration: Plate 15.
_Photo by D. Seth-Smith._
PEACOCK PHEASANT.
The display of this bird differs conspicuously from that of the Peacock
and recalls that of the Pigeon in some respects. The “ocelli” on the
wings afforded Darwin the interpretation he sought for as to the
meaning of the notch in the “eye” of the Peacock’s tail-feather.]
[Illustration: Plate 16.
_Photos by the Author._
“THE PEACOCK IN HIS PRIDE.”
In the upper figure it will be noticed the “train,” when erected,
encircles the base of the neck; the lower figure shows the train
supported by the tail and dropping on each side in front of the wings.
[Face page 96.]
The Argus Pheasant is an even more wonderful performer than the two
preceding species. In this bird, it should be remarked, the tail and
the secondary wing-feathers are enormously lengthened, the latter to
an extent met with in no other bird, showing that the struggle for
existence cannot be very severe with this species. For if long
journeys had to be undertaken in search of food, or to avoid extremes
of climate, or enemies had to be swiftly escaped, such cumbersome
wings would lead to speedy extermination. But an even more remarkable
feature of these wings is their wonderful coloration. The primaries
have blue shafts, and a most delicately mottled pattern formed by spots
of reddish chocolate on cream-coloured ground, while the secondaries
have their broad webs ornamented with large ocelli, to be described in
greater detail presently. When under the influence of sexual excitement
Darwin tells us, the wings are so spread as to form a deep concavity,
an effect which is gained by pressing the primaries close to the
ground, and turning the elbows upwards. Within this concavity lie the
ocelli, in radiating vertical rows. But to produce this effect the bird
has to turn its head under its wing, so that it lies behind the screen.
Hence it cannot see the female which is the object of these captivating
antics. As a consequence, to discover whether he has an audience for
she will often walk disdainfully away—he has constantly to thrust his
head through the curtain, and hence many of the feathers in this region
get much worn.
By nature it would seem the Argus Pheasant is a very solitary bird,
though we must assume it is polygamous. As the breeding season
advances, however, the male proceeds to choose some open space in the
depths of the forest—which it never leaves—and therefrom to clear all
the dead leaves, and twigs, for a space of some six or eight yards
square, so that nothing but the bare earth remains, and thereafter
this area is kept scrupulously clean. Here, in solitary state, for a
short season he remains, calling at frequent intervals to advertise the
fact that an eligible male is in the neighbourhood desiring mates. A
dozen times in succession he will break the stillness of the forest
gloom with a loud, “How-how, how, how, how!” Sooner or later comes a
responsive, “How-owoo, how-owoo!” and in a short time, guided by the
sound, one or more females discover the object of their quest. But the
pairing desire has not yet reached its full intensity, and doubtless to
kindle this the display just described is enacted, and not once, but
a dozen times probably, before the desired state of frenzy has been
aroused. Not seldom another male answers the cry, and this inevitably
leads to a duel whereby the fittest and strongest male is speedily
discovered.
A word as to these ocelli. This pattern is rare among birds, and Darwin
brought to light some extremely interesting facts regarding it. He was
led to investigate the matter by his curiosity as to the meaning of
the notch in the ocelli of the Peacock’s train-feathers. At last he
noticed that among the different species of Peacock Pheasants there was
one (_Polyplectron chinquis_), in which the ocelli were paired, one
lying on either side of the shaft, in another (_P. malaccense_) these
approached and partly fused with one another. Now, to get the indented
ocellus of the Peacock, we have only to imagine the fusion of two such
ocelli, whose long axes inclined obliquely to one another, to get the
“eye” of the Peacock with its indented lower edge; for such fusion
would give a continuous upper and an indented lower border.
The “eyes” of the Argus Pheasant are more interesting still, for, as
Darwin pointed out, these have the appearance, if the feathers are
held more or less vertically, of a number of balls lying each within
a socket, or cup: for each of these balls has a light area which
exactly simulates the light glancing across the upper pole of a sphere,
leaving the rest in shadow; and, singularly enough, this effect is
produced in the living bird only when the feathers are erected for
display. The probable steps in the evolution of these ocelli from
simple spots, and through elliptical bars, Darwin traced with his usual
skill and insight, and those who would follow this up should turn to
that wonderful book, “The Descent of Man.”
[Illustration: Plate 17.
PATTERNS WHICH PUZZLED DARWIN.
The notch in the “eyes” of the Peacock’s train-feathers puzzled Darwin
till he met with the ocelli of the Peacock-pheasant. The left-hand
lower figure represents the ocellus of the Argus, the right-hand that
of the Peacock-pheasant.
[Face page 98.]
It is probable that the erroneous interpretation of the display of the
Peacock is due to the more lasting and easily remembered impression
of what obtains in the case of the Turkey under like emotions. This
bird in his exultant moods, most people have seen. Herein the tail
plays a very important part, being raised and spread to form a great
half-circle, while at the same time the back-feathers, or at least
those of the lower back, are set on end, and the wings are trailed on
the ground. The effect is heightened by the suffusion of blood to the
bare skin of the head and neck, and the sudden inflation of a long,
pendent, fleshy wattle from the forehead, which hangs down over the
beak. Great display is made with this, and an additional importance is
added by the spasmodic vocal efforts which can best be described by
the “gobble” rapidly repeated, as the bird struts about with mincing
gait, turning the wheel-like tail now to one side now to the other.
But the Turkey possesses yet another “ornament” which commonly escapes
notice. This is the curious tuft of long, black, coarse, bristles which
projects forward in front of the breast. It is difficult to discern
what part this tuft may play, since it is quite inconspicuous. It seems
as though this must be added to the number of structural characters
which appear to survive without any apparent use.
The game-birds, it is significant to remark—and significant because
they are commonly polygamous—afford a quite remarkable series of
displays, only some of which can be summarized in these pages. In every
case, too, they are accompanied by conspicuous coloration and a more
or less excessive development of brightly-coloured plumes, or areas
of bare skin. In some, as in those wonderful birds the Tragopans, the
development of bare skin, vividly coloured, and produced into pendulous
folds, has attained a degree met with nowhere else among this group.
These flaps, or finger-like wattles, as the case may be, under the
influence of sexual excitement become turgid, and their hues enormously
intensified: though beyond this fact but little else is known of their
performances. In Swinhoe’s Pheasant the face is bare, the skin being
covered, as in the case of the common Pheasant, with tiny villi of a
vivid red colour. But when excited by the presence of a female the
upper part of this face area rises high above the head like a pair of
horns. With these turgid, and erect, the bird makes a series of short,
semicircular rushes around his prospective mate, accompanying each of
these gyrations with an angry hissing sound. The Golden, and Amherst
Pheasants are among the most gorgeously clad of birds. Not their least
conspicuous ornament is a cape-like frill of long, highly coloured
feathers of which the birds seem to be extremely conscious; for when
endeavouring to excite the female nearest him to the necessary pitch of
sexual desire, he places himself sideways before her, drawing the frill
round to the side facing her, and dropping the wing, in order, as it
would seem, that she may miss nothing of his resplendent livery. This
side of his nature he reserves for her. Intruding rivals are treated
after quite another fashion, for like most of the gallinaceous birds
his legs are armed with formidable spurs which can, and do, inflict the
most terrible wounds: as, indeed, has been shown from the evidence of
the Cock-pit in the case of game-cocks.
[Illustration: Plate 18.
THE “STRUTTING TURKEY.”
This should be contrasted with the Peacock. Herein the tail itself
is the principal ornament, the effect of which is heightened by the
erection of the back-feathers, and the vivid play of colour of the
“wattles” of the head.]
[Illustration: _Photo copyright by W. H. Quentin._
THE DISPLAY OF THE GREAT BUSTARD.
This is effected by the inflation of a great wind-bag in the neck, and
the eversion of the wing and tail feathers as described in the text.
[Face page 100.]
By way of contrast with the several displays just described, it would
be hard to find a more striking illustration than that afforded by
the Lesser Bird of Paradise (_Paradisea minor_), inasmuch as here the
display is associated with rivalry between a number of individuals.
For much of our knowledge on this subject we have to depend on the
descriptions of natives; but happily this has now been supplemented by
observations made by Mr. Ogilvie Grant on a captive in the Gardens of
the Zoological Society of London.
Impelled by the surging wave of sexual desire, as yet only seeking
consummation, these birds gather together at frequent intervals, on
certain of the forest trees of the Aru Islands, selected apparently
because they present an immense head of spreading branches, and large
but scattered leaves. Here ample space is found for the revels, which
take the form of “Sacaleli,” or dancing-parties, comparable to the
erotic dances of many barbaric races.
By the time the ball opens, the birds, to the number of twenty or more,
have worked themselves up into a state bordering on frenzy, and each
commences his performance with quivering wings and loud, penetrating
cries which may be syllabled as _walk—walk—walk—walk—walk—walk_,
rapidly repeated. Then the wings are suddenly held out on either side,
the tail is bent forward under the branch, and with a quick, barely
perceptible rustle, the gorgeous, golden, diaphanous side-plumes are
thrust upward and forward on each side of the body, forming an arched
cascade above the back. With every muscle tense the performer will
remain in this attitude from ten to twenty seconds, slightly quivering
the wings, and from time to time imparting a tremor to the upraised
plumes. Then follows a second phase. Each bird, seemingly possessed,
commences to dance and hop wildly backwards and forwards along the
bough, and with head bent forward, wings spread horizontally, and the
side plumes raised to their utmost, he gives vent to a series of loud
harsh cries—“ca! ca! ca! ca!” For some seconds he remains in a sort
of ecstasy, rubbing his beak on the bough, and occasionally glancing
backwards below his feet, and with the back fully arched. The climax
passed, he reverts once more to the earlier, more erect stage of the
display, when the paroxysm either gradually subsides or is renewed.
No less extraordinary is the behaviour of the King-bird of Paradise
(_Cicinnurus regius_), which has been described by Sir William Ingram,
who for a time had a captive in his aviaries. As the illustration
shows, its posturing is quite remarkable. Before this is described,
however, a brief description of its coloration should be given,
which, it must be remarked, cannot possibly convey more than a very
vague idea of its sumptuous character. Picture a bird no bigger than
a thrush, but of a wonderful cinnabar red, with a gloss as of spun
glass: the head clothed in short, velvety, orange-hued feathers; and
with a white breast, having the softness and sheen of satin, and
crossed by a band of deep metallic green, contrasting with the red
of the throat. Add a yellow beak, and legs of cobalt blue, and you
will have the features which catch the eye at the first glance. But a
little closer examination will reveal yet other points for wonderment.
Along each side of the body the upper flank-feathers become elongated
and delicately tinted, and, furthermore, they are erectile: so that
they can be raised up on each side of the body to form an almost
circular shield of delicate ash grey, bordered with buff and emerald
green. These play a most important part during the sexual frenzy,
and the effect thereof is not a little heightened by the middle pair
of tail-feathers, which have been modified to form a pair of slender
stalks, some ten inches long, bearing at the ends a curious disc of
emerald green formed by coiling upon itself—like a watch-spring—the
only piece of the vane of the feather which remains.
So much for its fine feathers; now for the manner of their use. “He
always commences his display,” writes Sir William Ingram, “by giving
forth several short notes and squeaks, sometimes resembling the call
of a quail, sometimes the whine of a pet dog. Next he spreads out
his wings, occasionally quite hiding his head; at times, stretched
upright, he flaps them, as if he intended to take flight, and then,
with a sudden movement, gives himself a half turn, so that he faces the
spectators, puffing out his silky-white lower feathers; now he bursts
into his beautiful melodious warbling song, so enchanting to hear but
so difficult to describe. Some weeks ago I was crossing a meadow and
heard the song of a skylark high up in the heavens, and I exclaimed at
once: ‘That is the love-chant of my King-bird.’ He sings a low bubbling
note, displaying all the while his beautiful fan-like side-plumes,
which he opens and closes in time with the variations of his song.
These fan-plumes can only be expanded when his wings are closed, and
during this part of the display he closes his wings and spreads out
his short tail, pressing it close over his back, so as to throw the
long tail-wires over his head, while he gently swings his body from
side to side. The spiral tips of the wires look like small balls of
burnished green metal, and the swaying movement gives them the effect
of being slowly tossed from one side to the other, so that I have
named this part of the display the ‘Juggling.’ The swaying of the body
seems to keep time with the song, and at intervals, with a swallowing
movement of his throat, the bird raises and lowers his head. Then comes
the finale, which lasts only a few seconds. He suddenly turns right
round and shows his back, the white fluffy feathers under the tail
bristling in his excitement; he bends down on the perch in the attitude
of a fighting cock, his widely-opened bill showing distinctly the
extraordinary light apple-green colour of the inside of the mouth, and
sings the same gurgling notes without once closing his bill, and with a
slow dying-away movement of his tail and body. A single drawn-out note
is then uttered, the tail and wires are lowered, and the dance and song
are over.
“The King-bird has another form of display which he very rarely
exhibits, and only on three or four occasions have I seen him go
through this performance. Dropping under the perch, the bird walks
backwards and forwards in an inverted position with his wings expanded.
Suddenly he closes his wings and lets his body fall straight downwards,
looking exactly like a crimson pear, his blue legs being stretched
out to the full length and his feet clinging to the perch. The effect
is very curious and weird, and the performance is so like that of
an acrobat suddenly dropping on to his toes on the cross-bar of a
trapeze that I have named this the ‘Acrobatic’ display. It has been
witnessed on different days to his ‘Juggling’ display. While giving his
‘Acrobatic’ performance he sings the whole time, but never shows his
side-plumes, and when he is in the pendulous position his body sways
gently as if it were influenced by a fitful breeze. The whole of this
performance takes but a very few seconds.”
[Illustration: Plate 19.
_From a Drawing by Roland Green, Jun., adapted from G. E. Lodge and
others._
SOME OF FORTUNE’S FAVOURITES.
The Birds-of-Paradise have few rivals in the matter of ornament. In the
centre of this plate are seen the Lesser and the King Bird-of-Paradise
displaying (after G. E. Lodge). The first-named is distinguished by
the enormous development of the side plumes, which can be raised high
above the back. In the second, the ornaments take the form of erectile
frills on each side of the breast, and strangely modified tail-feathers
which end in curious discs. At the top left-hand corner is the
King of Saxony’s Bird-of-Paradise; on the right is the Long-tailed
Bird-of-Paradise; at the bottom of the page, from left to right, are
Hunstein’s, the Six-wired, and Superb Bird-of-Paradise.
Face page 104.]
Naturally one needs to witness such a display to appreciate its beauty
and its weirdness; but the wonderful sketches which my friend, Mr. G.
E. Lodge, made during one of these performances, should go far towards
helping the reader to visualize what really takes place.
While it would be untrue to say that the Birds of Paradise are of a
more amorous, or more excitable disposition than other less resplendent
birds, one cannot but be impressed with the fact that they exhibit
a range of variation in the matter of feather-ornament probably
unequalled, and certainly unsurpassed, by any other group of birds.
From what has been observed of the few species which have been kept
in confinement, they seem to enjoy no less distinction in matters of
display. On this latter subject no more of importance can be said, and
exigencies of space forbid any attempt to describe the exquisite beauty
of coloration which a survey of all the known species reveals. It would
be hardly more profitable to attempt to describe the varied character
of the shields, crests, frills, streamers, which are to be met with
in different species: but a glance at the accompanying illustrations
will show that it would be hard, indeed, to exaggerate the splendour
of the ornamentation which these birds have developed. Even here,
where no indication can be given of the glowing, vivid colours, often
indescribably beautiful, it is obvious that these birds well deserve
their name. St. John’s imaginary Paradise would probably have been
described in far more enticing language had he known of the existence
of these wonderful birds.
Among all the known species the dullest is Wallace’s Bird of Paradise,
the general coloration being of a dull brown hue; but even here, a pair
of wing-coverts are produced into long, broad streamers, unique among
birds; while the feathers of the throat and flanks are of a marvellous
metallic green, the flank-feathers being produced to form a long,
pointed tuft.
To what factors must we attribute the growth of these wonderful
colours, these strange outgrowths, frills, and tufts, and streamers,
the like of which is almost unparalleled? In a group numbering some
fifty or more species there is not one that does not display some
strange feature. We cannot attribute it to the environment, for in such
case the results should have produced uniformity; nor can we invoke
the aid of sexual selection save in a very indirect manner, and in a
sense other than generally understood by this term. It seems, then,
not unreasonable to suggest that they are the expression points of the
internal metabolism: the manifestations of that tendency to vary which
is inherent in every fibre of the organism. But no attempt shall be
made to elaborate this theory till more evidence has been taken. The
humming-birds, and the game-birds, are perhaps the only other groups
which exhibit quite such a prodigality of ornament; of the latter,
instances have already been cited.
So far the displays which have been described have been such as
are confined to the use of more or less resplendent plumage. There
are, however, many species which contrive to secure most startling
results, not so much by the parade of coats of many colours as by
grotesque changes of shape produced by wind-bags of various kinds. The
Pouter-pigeon affords a case in point. This bird possesses the power of
inflating the gullet to an enormous size, so as to produce a strangely
distorted form, at any rate, to our eyes. The “Pouter,” it is hardly
necessary to mention, is an artificial product of the “fancier,” who
has taken advantage of the natural tendency, seen in the Wild Pigeon,
to inflate the neck during moments of excitement. By the selection from
each generation of the finest performers in his stock, the Pouter of
to-day has been developed. But there are many birds which, while not
even remotely related, have developed the same strange device. The most
striking illustration of this kind is furnished by the Great Bustard, a
bird once common on the fen-lands of Great Britain, but now, unhappily,
exterminated within these islands.
The means of inflation in this case is afforded by a large thin-walled
sac of a very remarkable character. Opening by a small slit just under
the tongue, it is continued down the front of the neck immediately
under the skin, which in this region is thickened by an accumulation
of fat and blood-vessels. Between the arms of the furcula, or
merry-thought, its cavity is constricted, to expand again immediately
to form a pear-shaped termination. How it is filled is something of
a mystery. But once inflated, the bird draws its neck downwards and
backwards, so that the head is brought to rest between the shoulders
and is there almost buried, partly by pressure on this curious
air-cushion and partly by the erection of a number of bristle-like
feathers, which in calmer moments project backwards on each side of
the head. At the same time the tail is drawn forwards to lie upon the
back, thus exposing a billowy mass of white feathers forming the under
tail-coverts. The tips of the wing-feathers are used to hold the tail
in position. Meanwhile the scapulars are set on end, and the long inner
secondary quills are similarly erected. The feathered contortionist,
having completed his preparations, now approaches his partner with a
mincing gait, then halts before her and solemnly utters a series of
low grunts like “oak, oak, oak.” Having thereby declared his passion,
and commonly without gaining any answering response, he returns to his
normal shape again!
It is curious that a near relative of this bird, the Great Australian
Bustard (_Eupodotis australis_), also captures the wind to declare
his love; but it is disposed of after a quite different fashion,
being drawn into the gullet, though the precise manner in which it
is manipulated demands further investigation. The display Dr. Murie
described many years ago. It begins, he tells us, with a swelling
of the throat, while the head is thrown upwards. Immediately after,
the neck swells, and the feathers of the lower part of the neck, set
all on end, are carried downwards, apparently surrounding a huge bag
which reaches nearly to the ground. During all this time the head and
neck are held rigid and point skywards, the head surmounting a great
feathery column. Meanwhile the tail, as with the Great Bustard, is
drawn forwards over the back. In this peculiar attitude the bird struts
about in a stiff, waddling manner, the elongated neck-bag swaying to
and fro and the feathers of the throat standing out in the shape of a
great rounded swelling. The acme of inspiratory effort completed, the
bird begins to snap the jaws together, producing loud noises, which are
accompanied by a soft dove-like cooing.
The Pectoral Sandpiper in like manner inflates its gullet. But, unlike
the Pigeon and the bird just described, the neck is not markedly
straightened, nor is the body raised. As the air is drawn in, the
gullet expands, till it forms a great spherical drum. Then the excited
performer runs along the ground uttering a resonant “too-u tooo-u”
repeated seven or eight times in rapid succession, all the while he
approaches nearer to the apparently very much-otherwise-engaged female.
This effort failing, he will then often rise on quivering wings twenty
or thirty feet into the air, and dive gracefully down again immediately
afterwards, deflating this curious balloon to await a more favourable
opportunity.
In some species where wind-bags are employed as aphrodisiacs the outer
skin is brilliantly coloured and exposed during the display. The
Prairie-hen affords a case in point. In this species the air-chamber
is furnished, not by the gullet, but by the air-sacs of the neck. When
these are inflated they appear as two large orange-coloured bodies
standing boldly out among the feathers. Their effect is heightened by
a tuft of long stiff feathers which are thrust forward like a pair of
horns, on each side of the head, while at the same time the feathers of
the back are set on end, the tail is spread like a great fan, and the
wings are half opened and trailed like those of the Turkey.
The displays take place in the early hours of the morning, when parties
of from a dozen to fifty, of both sexes, meet on some slight knolls
where the grass is short. Having duly assembled, the more ardent cocks
immediately begin to prepare for the morning revels, the first part of
the performance apparently being of a comparatively passive nature—the
parade of the air-sacs and the erection of the feathers.
Then some “proud cock, in order to complete his triumph, will rush
forward at his best speed ... through the midst of the love-sick
damsels, pouring out as he goes a booming noise ... which may be
heard for at least two miles in the morning air. This sound is by no
means harsh or unpleasant. When standing in the open prairie at early
dawn listening to hundreds of different voices pitched in different
keys, coming from every direction and from various distances, the
listener is rather soothed than excited.
“Every few minutes this display is repeated. I have seen not only one,
but more than twenty cocks going through this funny operation at once;
but then they seem careful not to run against each other, for they have
not yet got to the fighting point. After a little while the lady birds
begin to show an interest in the proceedings by moving about quickly, a
few yards at a time, and then standing still a short time.
“The party breaks up when the sun is half an hour high, to be repeated
the next morning, and every morning for a week or two before all make
satisfactory matches. It is towards the latter part of the love-season
that the fighting takes place among the cocks, probably by two who have
fallen in love with the same sweetheart....”
There is much that is extremely interesting in this account and a
little that seems to have been misinterpreted. The fact that these
antics are repeated during many days until at last the females are
moved to display some interest is just what we should expect if this
demonstrative behaviour on the part of the males acts, as we believe,
as an aphrodisiac. And that actual fighting occurs is highly probable,
but there can be no doubt that in such case the whole aspect of the
bird must be changed, for anything in the nature of fighting with the
delicate air-sacs inflated would greatly endanger the most important
aid to success in achieving this object which these birds possess.
[Illustration: Plate 20.
_Photo from The Museum of Natural History, New York._
THE LOVE-MAKING OF THE PRAIRIE HEN.
During the “display” large, yellow, air-sacs in the neck are inflated.
The bird in the foreground shows one of these, and the ornamental
feather frill, very clearly.
[Face page 110.]
No less remarkable is the performance of the Frigate-bird (_Fregata_),
a tropical species allied to the Pelicans and Boatswain-bird, and to
our own more familiar Cormorants and Gannets. It might well be called
a marine Swift, having excessively short legs and small feet, and a
wonderful expanse of wing. As with the Swifts, of course most of its
time is spent on the wing; the feet are only useful for supporting the
body when ashore, they are never used for walking, at any rate, for
more than a few steps. The wings afford the only means of locomotion.
Our knowledge of these birds when under the stress of sexual excitement
we owe to Dr. C. W. Andrews, who had the good fortune to study the
species known as the Great Frigate-bird (_Fregata aquila_) during his
task of surveying Christmas Island (Indian Ocean).
“About the beginning of January,” he remarks, “the adult males begin
to acquire a remarkable pouch of scarlet skin beneath the throat; this
they can inflate till it is nearly as large as the rest of the body,
and a dozen or more of these birds sitting on a tree with outspread,
drooping wings and this great scarlet bladder under their heads are a
most remarkable sight. When a hen bird approaches the tree the males
utter a peculiar cry, a sort of ‘wow-wow-wow-wow,’ and clatter their
beaks like castanets, at the same time shaking their wings. When
they take to flight the air is allowed to escape from the pouch, but
occasionally they might be seen flying with it partly inflated.”
Here again there can be no doubt about the purpose, or perhaps one
should say the stimulus, of this strange performance. This pouch,
I have been enabled to ascertain from dissection, is not formed by
inflating the gullet, but, as in the case of the Prairie-hen, by the
enlargement of the air-sacs of the neck.
These air-sacs, which are present in all birds, are only enlarged to
further the ends of sexual display in a few species, and, curiously
enough, these are in no way related one to another. The Adjutant
storks, it may be remarked in this connection, have used the air-sacs
which are fed by the nasal system instead of those fed by the lungs,
as in all the species so far described. When deflated this pouch forms
a quite inconspicuous conical swelling in front of the neck; under the
stimulus of excitement, it awakens as it were into activity, and is
suddenly transformed into a great red or red-and-black bag, encircling
the neck and projecting far downwards in front of it, only to be
deflated an instant later with a speed which leaves one gasping.
The specialization of the air-sacs, that is to say their transformation
to perform new functions subservient to the ends of sexual activities,
is not exclusively confined to display. In at least one instance an
air-sac has been specially developed to act as a voice resonator.
This is furnished by the Emu, wherein the wind-pipe, near the middle
of its length and on its anterior aspect, has a number of incomplete
rings forming a long slit. The lining of the windpipe escapes from
this slit in a hernia-like pouch, and takes up a position beneath the
skin. Even when inflated this pouch gives no very obvious sign of its
existence, but it serves to produce a curious hollow, drumming sound,
like the boom of a big drum softly beaten. But why it should have been
developed, when the Ostrich and the Cassowary produce similar but
louder “music” without any special apparatus whatever, is a mystery. At
least one species of Cassowary can emit a roar which would do credit
to a lion.
In the males of all healthy animals the periodic stimulus to
reproduction finds expression in more or less striking eccentricity
of conduct. Sometimes, as the foregoing instances have shown, this
has been exaggerated by the development of long, resplendent plumes:
sometimes by brilliant coloration, displayed either by the plumage or
by bare areas of skin, or by both, while in not a few cases attitudes,
to our eyes grotesque and made still more so by the aid of inflatable
pouches, are the outward and visible sign of the raging fires within.
For the completion of this chapter yet other instances of this kind
must be cited, instances which reveal a further elaboration of some
of the more striking of these tricks of posturing; or which concern
the growth of the aggressive instincts, which are proclaimed by the
development of armature often of a very formidable character. As the
sequel shows, however, there are no hard and fast dividing lines
between these several modes of expression.
That remarkable bird, the Ruff (_Machetes pugnax_), now, alas! no
longer to be met with in our fens, exhibits a curiously composite
character in the phases of its love display.
Preparations for this are begun in the early spring by the assumption
of what is called a “nuptial dress,” which is worn only by the male,
and which contrasts in a very conspicuous manner with the plumage worn
during the rest of the year. The most striking features of this dress
are the great, erectile, Elizabethan ruff which encircles the neck
immediately behind the head, and the long, tongue-shaped “ears” which
surmount the head itself. These exhibit a most remarkable diversity
in their coloration, and it is no exaggeration to say that no two are
ever alike. Red, cream-colour, buff, black, white; spotted, streaked,
freckled and barred are the only descriptions that can be applied to
them, for the combinations of their hues and patterns seem infinite.
Having grasped this fact, the eye next turns to the colouring of the
rest of the body, and it will be found that here too is the same
diversity, though less conspicuously so; and finally it will be noticed
that at this time the feathers around the base of the beak have been
replaced by yellow or orange-coloured papillæ. The females also now
wear a dress differing from that of the so-called “winter plumage,”
but it does not present any very striking features nor any form of
ornamentation comparable to that of the males.
The Ruff is a polygamous bird, which, in its display, presents some
curious and puzzling features, one of which consists of a sort of
tournament between rival males. At the break of day the performers,
selecting such eminences as the fen-lands afford, assemble apparently
to display their finery, for a couple of males will often stand facing
one another with frills erected and beaks touching the ground, silent
and immovable, for perhaps half a minute. Sooner or later, however,
they will commence to spar, and this presently leads to blows, during
which one of the combatants will attempt to seize the other by the
wings. However, no damage seems to be inflicted during such encounters,
which are by no means aimless or profitless, for during such bouts the
weaker, less vigorous birds are driven from the field, and the victor
in consequence wins for himself a larger harem.
When the actual pairing time arrives the parade of the frills begins
again. The amorous instincts, it is important to notice, are awakened
earlier in the males, so that by the time the females have attained to
a like condition the least mettlesome males have been driven off. What
follows is not the selection by the females of the finest performers
so much as a process of sorting out, whereby the females discover and
cleave to those males which are readiest for mating. This display
succeeds in revealing both the most mettlesome males and the most
amorous females, who, however, would seem to require great persistence
and much demonstration on the part of the males before they can be
finally aroused to the pitch necessary for pairing. Again and again a
male may be seen to approach an apparently very unconcerned female,
and then to crouch down before her with his beak pressed to the ground
and his frill and “ears” set off to their fullest. For some seconds
he will remain lost in apparent contemplation, then with a dazed,
far-off, expression he will look up, to find, as often as not, that
she is still apparently feeding, quite unmoved by his protestations;
or that she has even flown off and left him. Pursuit speedily follows,
and the performance is repeated until at last she too catches the flame
of passion and permits, or rather invites, the final act of sexual
congress.
Though these birds on occasion will fight, and savagely, they cannot
inflict serious damage on one another by reason of the relative
feebleness of their beaks and legs, which are but ill-adapted for
violent measures. Inasmuch as the Ruff is a polygamous species,
these bloodless battles have a peculiar interest. They show that
the preponderance of females, which polygamy implies, is not, as is
commonly supposed to be the case, due to a high death-rate among the
males by fighting. The same is true of the Wydah-birds, and their kin,
the only polygamous species among the Passeres.
In this connection it is to be remarked that fighting, of a more or
less sanguinary character, is apparently universal among birds, the
conflicts being waged not so much in the way of squabbles for the
possession of females as for the acquisition and retention of territory
and all that this entails during the breeding season and, to a much
less extent, in the defence of the eggs and young. But to this point
we must return. For the moment it will be more profitable to focus
attention on the character of this fighting. In the first place, it
is by no means necessary that the combatants should be armed. The
“dove of peace” at this time of the year appears in a new and not
always pleasing light, for not only will he fight his neighbours,
but he does not always show that gentleness towards his wife with
which tradition has credited him. The little Humming-bird would seem
to be as little capable of fighting as a bird could be, yet few are
more pugnacious. The naturalist Gosse tells of a pair which had torn
one another’s tongues out in their blind fury; and everybody knows
that Robins and Tits fight savagely to preserve their chosen haunts
from invasion by their neighbours. In some birds this pugnacity has
become an overmastering passion. Some of the Quails, and a species
of Rail (_Gallicrex cristatus_), a near relation of the Moorhen, are
commonly kept by the natives of the East, as our forefathers kept
Fighting-cocks, for the sake of seeing them fight one another. Yet,
save in the case of the Fighting-cock, neither of these birds possesses
any aggressive weapons.
Among the game-birds, however, powerful armature, in the shape of
long, pointed, spurs on the legs are met with. In the Jungle-fowls
and Pheasants only a single pair are found on each leg, but in other
species, as in the Francolins, there are several pairs, and these
birds, it is instructive to notice, are notorious for the ferocity
of their encounters. It is said that in the Indian Swamp-Francolin
(_Francolinus gularis_) nearly every individual is marked by scars and
wounds received in duels with rivals.
Certain members of the Plover-tribe, and certain Anserine birds, have
developed spurs of a very formidable character on the wings. Among the
Plover-tribe the best example of such armoured species is the Egyptian
Spur-winged Plover (_Hoplopterus_). This bird, after the fashion
of its unarmoured relatives, such as the Common Lapwing, fights by
turning suddenly in the air and striking with the wings. In the case
of the formidably armed Egyptian bird the result is often fatal; but
with our Lapwing a fatal result is rare, since but slightly swollen
knobs take the place of spurs. In Hoplopterus and in the Jacana this
spur arises from the base of the thumb, but in the Spur-winged Goose
(_Plectropterus_) it is borne by one of the wrist bones (the radial)
while in the aberrant Geese-like birds (_Palamedea_ and _Chauna_) there
are two spurs on each wring, one at each end of the metacarpus. That
these weapons have come into being in response to need seems a very
natural conclusion, but it is one which presents many difficulties
when more closely examined. The wing spurs, differing widely in their
nature as they do, in one case borne on a carpal bone, in others on the
metacarpus, seem rather to owe their origin to fortuitous variations
which have become, so to speak, adopted by selection, than to a
response to the oft-repeated stimuli incidental to fighting. The latter
explanation is Lamarckian and to-day finds favour with but few. The
stimulus theory seems to be effectually discounted by the existence
of the spurs on the legs of gallinaceous birds. That these owe their
origin to impacts, or blows, seems more than doubtful: and one can
hardly see how they could have served any useful purpose until they had
attained a sufficient length to serve as weapons. Even if we suppose
that the spurs of, say, the Jungle-fowl or the Francolin have been
derived from tuberosities such as are found on the legs of the French
Partridge (_Caccabis rufa_), we should still lack evidence that the use
of the legs in fighting caused the origin of the tuberosities.
There is yet another puzzling feature in regard to the armature of
the wings, and one which may yet help to a better understanding of
the puzzles presented by spurs. A Jacana, one of the Plovers, has the
radius broadened or flattened out from its middle onwards to form a
flat plate or blade, but the use thereof is unknown. It may possibly
serve as a weapon of offence, enabling the bird to beat its rivals with
its wings, but from the nature of the structure, and of the effect
such a use of the forearm would have upon the hand, it seems doubtful
whether it serves any aggressive function. If used at all in fighting
it is probably during fights in mid-air, when, after the fashion
pursued by the Spur-winged Plover, and even in the case of our own
Lapwing, a blow is struck by the uppermost bird at its rival, and often
with fatal effect. It is significant to remark, by the way, that in
the Lapwing a tubercle answers to the spur of Hoplopterus just as the
tubercles of the French Partridge (_Caccabis_) answer to the spur of
the Jungle-fowl or Pheasant: but the flattened radius of the wing of
the _Metopidius jacana_ has no parallel.
With birds, as with men, there must always remain the ability to
appeal to force when some important end cannot otherwise be gained.
The species which adopts the crazy tactics of the Quaker is doomed to
extinction, sooner or later. The foregoing instances display force, as
we may say, aggressively. But even the peacefully disposed birds can
fight when aroused.
Reference has already been made to dancing in this chapter; but so far
no very striking instances thereof as a form of sexual display have
been cited. The subject has been deferred because this peculiar type of
activity is not always directly associated with the _furor amantium_.
With some species, which, it should be remarked, also lack distinctive
colouring, the erotic state is manifested apparently not so much by the
display of expanded wings and tail as by frenzied dances. The Jacanas,
aberrant members of the Plover tribe resident in South America, are
expert performers, displaying moreover a curious spontaneity during
such outbursts. A flock will be apparently sedulously feeding when
suddenly and with quick, excited gestures all will cluster together in
a group and go through a singular and pretty performance, holding their
wings outstretched and agitated, some with a fluttering and others with
more leisurely movement, like that of a butterfly sunning itself. The
performance over, all scatter and feed again.. The Honourable Walter
Rothschild, in his “Avi-fauna of Laysan” tells us of the stately
Albatross, which breeds, or rather bred there—for the Japanese display
a singular callousness in regard to animal life where commercial
interests are concerned in thousands: “First they stand face to face,
then they begin nodding and bowing vigorously, then rub their bills
together with a whistling cry. After this they begin shaking their
heads and snapping their bills with marvellous rapidity, occasionally
lifting one wing, straightening themselves out and blowing out their
breasts; then they put their bills under the wing or toss them in the
air with a groaning scream, and walk round each other often for fifteen
minutes at a time.”
Cranes are much given to dancing. Mr. Nelson, an American
ornithologist, has described with much vigour the dancing of the
Sandhill Crane in Alaska. As he lay in a “hunting-blind” he was
suddenly aroused by the arrival of a crane, followed speedily by
a second, uttering his loud note as he came, until he espied the
first-comer on the ground, when he made a circuit and dropped close
by. Both birds then joined in a series of loud rolling cries in quick
succession. Suddenly, the last-comer, which seemed to be a male,
wheeled his back towards the female and made a low bow, his head nearly
touching the ground, and ending by a quick leap into the air. Another
pirouette brought him facing his charmer, whom he greeted with a still
deeper bow, his wings trailing loosely by his sides. She replied by an
answering bow and hop, and then tried to outdo the other in a series
of spasmodic hops and starts, mixed with a set of comically grave and
ceremonious bows. The pair stood for some moments bowing right and
left, when the legs appeared to become envious of the large share
taken in the performance by the neck, and then would ensue a series
of skilled hops and skips, like the steps of a minuet. Such antics
are characteristic of the Cranes of all species, and sometimes a
whole flock will join in such dances. But, it is to be noted, they are
not necessarily signs of the _furor amantium_: they certainly always
accompany this, but frequently they are indulged in, apparently, solely
as an outlet for exuberance of feeling.
Before the theme of dancing can be dismissed the performance of a small
species of perching bird, one of the South American Manakins, must be
described. The natives call it the “Bailador,” or dancer. In an account
of his travels in Nicaragua Mr. Nutting tells us: “I once witnessed one
of the most remarkable performances it was ever my lot to see. Upon a
bare twig ... at about four feet from the ground, two male ‘bailadors’
were engaged in a song and dance act that simply astonished me. The two
birds were about a foot and half apart and were alternately jumping
about two feet in the air and alighting exactly on the spot whence they
jumped. The time was as regular as clockwork, one bird jumping up the
instant the other alighted, each bird accompanying himself to the tune
of to-le-do—to-le-do—to-le-do, sounding the syllable to as he crouched
to spring, le while in the air, and do as he alighted. This performance
was kept up without intermission for more than a minute, when the birds
suddenly discovered they had an audience and made off.” Here again we
have no evidence of the _furor amantium_; nor that any females were
spectators of the scene.
It is important to notice that Mr. Howard, in the course of his study
of the Warblers, witnessed a performance having some likeness to this
on the part of three young Sedge Warblers but newly escaped from
the nursery. And this not in some solitary instance, but on several
occasions. Just after leaving the nest, he remarks, they are very
playful, “their games sometimes taking the form of a tilting match.
Three take part; two sit on convenient twigs facing one another, and
the third, from the central position, might almost be called an umpire.
Numbers One and Two lower their heads, each in anticipation of the
other moving; one of them, call him Number One, then springs into
the air and darts at Number Two: Number Two dodges and occupies the
position vacated by Number One; each of them then faces round ready to
continue the fray, the change of positions becoming quite rapid.” But
no recurrence of these antics has been noted during the course of the
adult sexual display, which is confined to posturing and displaying the
outspread wings and tail. Nevertheless there can be no doubt but that
such games in later life are incorporated, in the case of many species,
with the love display.
That the reproductive glands have played, and still play, a by no means
unimportant rôle in Evolution is shown by the history of the secondary
sexual characters. Among the birds, at any rate, the early stages of
physical changes belonging to this “figuration” are to be seen in
various forms of posturing, which in their more elaborate developments
we call “dances.” In many cases, as for example among the Warblers, the
periods of sex-emotion are marked by posturing alone. But in a number
of species, as has already been shown, the products of the sexual gland
seem to have undergone some further elaboration which has resulted in
the additional phenomena of gaudy coloration, in hypertrophied plumes,
and in weapons of offence.
But not yet is the list of such sexual products exhausted, for no
mention has so far been made of the development of the many wonderful
devices for the production of peculiar and arresting sounds, musical
and otherwise. These are of two kinds: one wherein certain feathers
have been modified to produce rhythmical notes either by percussion or
by vibration; the other wherein the internal organs have been modified
to produce musical notes or loud, resonant cries.
Instances of the latter kind are innumerable, and as a consequence no
more than one or two can be cited in these pages. The facts associated
with the production of vocal, as distinct from instrumental, music are
both curious and puzzling. To begin with, this music is produced by
the lower end of the trachea or windpipe, which has become modified in
various ways, though not so strictly in relation to the sounds produced
as is commonly supposed. The anatomical details of these modifications
cannot, or rather need not, be described now, save in the most general
terms.
Briefly the syrinx, or organ of voice, of birds, is formed in part by
the lowermost rings which form the tubular windpipe, and in part by
the smaller pair of tubes which, running therefrom to the lungs, form
the bronchi. These last are formed of semi-rings only, the inner wall
of the tube being formed by very delicate translucent membranes. As
air is forced from the lungs along the bronchi and up the windpipe,
the modulation of the voice is effected by muscles which regulate the
amount of air driven through the syrinx, and the height of the column
in the tube; the latter being effected by muscles which alternately
lengthen and shorten it.
So far so good. Next it is to be noted that this syrinx presents
a great variety of modifications, or types, differing not only in
plan, but also in the number and distribution of the muscles for its
manipulation. The most accomplished performers are to be found among
that great group of birds known as the Passeres, or perching birds,
wherein the number of these muscles is never less than five pairs,
and generally rises to seven. This association of musculature with
performance is exactly what we should expect. In Nature, however,
it is always the unexpected that happens. In the first place, the
females are, so far as the dissecting-knife and the microscope can
show, as well provided as the males, yet they do not sing. In the
second, the Nightingale and the Crow are equally endowed, so far as
we can discover, yet it is unnecessary to state that the talents
which the Crow possesses are never used! More disconcerting still
is the reflection that the Parrot, which is far less generously
endowed by Nature in so far as singing muscles are concerned, is
a much more skilful performer, inasmuch as it will reproduce with
equal fidelity the human voice and the song of the Canary! The latter
feat, at any rate, has been accomplished with amazing accuracy both
by the little Budgerigar (_Melopsittacus undulatus_) and the Quaker
Parrot (_Myopsittacus monachus_). In their wild state the Parrot
family are notorious for their discordant cries. It is therefore the
more remarkable that such feats should be capable of attainment. But
wherefore the elaborate syrinx of the Nightingale, if the simple type
seen in the Parrot is capable of the same result, and why the elaborate
syrinx in the case of the Crow, which never attains to a greater
perfection of vocal effort than the wild Parrot?
One speaks of the syrinx of the Parrot as of a simpler type because of
its feebler musculature and the lesser complexity of its framework, but
it is nevertheless a more efficient instrument, since it is capable
of reproducing both the human voice and songs such as that of the
Canary. This fact becomes still more remarkable when we reflect that
the natural voice of the Parrot, as we have just remarked, attains to
no more than a harsh screech. How is it that, capable of so much, it
has achieved so little? The same question may be asked in the case of
the Raven. This bird has a syrinx indistinguishable from that of the
Nightingale, save in point of size; yet the Raven’s voice is never
musical, nor can it be trained to such an achievement. Like the Parrot,
however, it can be taught to speak, though its vocabulary is never
so extensive. One would have imagined that when the syrinx of, say,
the Raven, or any of the Crow tribe, was compared with that of the
Nightingale or the Skylark, some structural differences, commensurate
with the difference in performance, would be discovered; but such is
not the case.
What interpretation are we to place on these paradoxical facts? One
cannot help asking why seven pairs of muscles should have been produced
by one group of birds to perform what can as easily be achieved in
another by two? It is true that the more generously endowed species
are musicians by birth, the others only by training. But one cannot
make a silk purse out of a sow’s ear. In like manner one asks why male
and female, possessing precisely similar voice-organs, should not sing
equally well, but they do not. Evidently mere mechanism does not alone
answer these questions.
Some, perhaps, may see in them instances of what is known as
“Hypertely,” wherein the bounds of mere utility seem to be transcended.
Hypertely, however, implies something more than this: it implies a
shooting beyond the mark, the overdoing of a feature, where the
momentum gained, from some obscure cause, keeps on being increased by
cumulative inheritance: and not being checked by Natural Selection,
causes the species in respect of such characters to pass beyond its
congeners. Professor Lloyd Morgan’s theory of “over-production” would
seem better to apply here, though in a somewhat different sense from
that used by him. For in the instances just quoted there is a latent
potentiality for response to new demands which the struggle for
existence may make, but a potentiality varying in degree, and here
selection finds its _métier_.
Yet further illustrations of secondary sexual characters, such as are
concerned with vocal music, must now be considered. The discussion of
these has been designedly deferred. They embrace instances of voice
production more singular than any yet referred to, and if possible more
difficult to interpret.
The facts first to be reviewed concern the syrinx of certain of the
Anatidæ. It is noteworthy that each of the three divisions of this
group—the Swans, Geese and Ducks—contains species in which either
the syrinx or the windpipe has acquired some singular feature. In
the surface-feeding Ducks, modifications of the syrinx are most
frequently found. Commonly, as in the Mallard, this takes the form
of a spherical bony case; in the diving Ducks this bony chamber
has enormously increased in size. Furthermore it has conspicuously
changed both in form and character: for it is now roughly trihedral in
form, and its walls present large _fenestræ_ closed only by delicate
membrane, suggesting that the increased size of the chamber has not
been accompanied by a corresponding increase of bony tissue for its
construction. Hence all that is available is used for the construction
of girders to form supports for the now membranous chamber walls.
Some species seem to show that this fenestration has been pushed to
excess, leaving only vestiges of this singular chamber, as is shown in
PI. 21. In some species the bronchi are much swollen, and the syringeal
chamber has entirely disappeared: in others, as in the Merganser and
Goosander, a large syringeal chamber is supplemented by dilatations of
the windpipe.
[Illustration: Plate 21.
GRADES OF EVOLUTION IN THE SYRINX OR ORGAN OF VOICE IN THE MALES OF
SURFACE FEEDING AND DIVING-DUCKS.
1. Wigeon. 2. Common Sheldrake. 3 and 4. Red-crested Pochard. 5.
Red-crested Merganser. 6 and 7. Long-tailed Duck. 8. Steller’s Eider.
9. Common Scoter.
Face Page 126.]
Save in the case of the Goosander, these peculiar structures are found
only in the male, but in the species first named the male, in addition
to the syringeal chamber, has two fusiform swellings in the windpipe,
one above the other: in the female one of these swellings is present,
but there is no syringeal box.
This box is generally, and probably correctly, regarded as a sort of
musical instrument. Nevertheless the males are far less vociferous than
the females which have no such voice resonator. One has only to listen
to, and compare the notes of the Mallard drake and duck to discover
this fact. Here, then, we seem indeed to have a case of “Hypertely.”
Before, however, we build too much on this we must discover whether the
sibilant sounds uttered by the males do, or do not, play an important
part in arousing the sexual passions of the females.
Certain of the Swans and Cranes afford illustrations of musical
instruments of an even more remarkable kind. Herein the windpipe at the
base of the neck enters a large chamber formed by the absorption of the
diploe sandwiched between the outer walls of the keel of the breastbone
and the enlargement of the space so created until it can accommodate
the tubular windpipe. This, entering the cavity in the form of a
loop, runs the whole length of the keel, the upper limb of the loop
finally running to the lungs. That we have here an indubitable musical
instrument there can be no question, for its possessor is enabled
thereby to utter loud, trumpet-like, if harsh, sounds. Here again only
the males are so provided.
The profound interest of this really extraordinary association of
unrelated structures has never attracted the attention it deserves.
Originally, no doubt, one would have met with nothing more than a
loop of the windpipe impinging against the anterior border of a
normal, blade-like keel: later there would have been formed a broad
shallow surface on the keel at the point of contact with the loop, and
gradually the depression must have deepened till the bony chamber came
into being. By what nexus of sympathy were these reciprocal responses
made?
Another very singular type of looped windpipe is that wherein the
trachea forms a series of coils between the body and the skin. It
is surely somewhat surprising to find that precisely similar coils
are met with in widely different groups of birds. Among the Passeres
they occur in the Manucode: among the Plovers in the Painted Snipe
(_Rhynchea rostratula_): among the game-birds in some of the Curassows,
and among the Anatidæ in the aberrant Australian Black-and-White Goose
(_Anseranas_).
Very little is really known of the part played by these musical
instruments of the Anatidæ, nor, for the matter of that, of most of
the “musicians” among birds. Of some of the game-birds more has been
gleaned, and among these surely the most interesting is the love-song
or “lek” of the Capercaillie. With the advent of April the cock, just
before dawn, repairs to some favourite tree—used year after year—and
there performs a most astonishing if unmusical serenade; with
outstretched neck, drooping wings and spreading tail he gives forth a
weird, uncouth kind of song, more or less divisible into three parts.
He begins with a series of notes which remind one of nothing so much as
the sound made by two sticks knocked together at intervals of ten to
fifteen seconds, getting quicker and quicker, and changing in key till
at last they become bell-like. Then follows a series of sounds like
the drawing of a cork out of a bottle, and these end with bird-like
twitterings. By this time, however, the singer has worked himself up to
an ecstasy of fervour and passion so intense as to deaden him to all
that may be passing in the outer world. During these moments no sound
disturbs him, partly, apparently, because the excitement of the “song”
causes a turgid condition of the blood-vessels which for the time
effectually deafens him. “Sportsmen,” in Swedish and other European
forests, knowing this, select such performances as affording the most
favourable time for Capercaillie shooting, only cocks being selected.
A survey must now be made of some of the more remarkable cases whereby
more or less musical, or rhythmical, sounds are made by instruments
of percussion; or by rapid vibrations. These are in almost every
instance formed by varying grades of modification in the feathers of
the wings or tail. Their presence, and their use, seem natural enough
until we recall the fact that many other birds without any apparatus
whatever, make sounds in no way less remarkable or less penetrating.
Pigeons, Nightjars and Owls, for example, can produce at will curious
snapping sounds by bringing the wings smartly together over the back.
The White, and Shoebilled Storks make castanets of the beak, throwing
the head backwards till the point of the beak touches the back, when
the jaws are set rapidly clashing one against another, producing a
sound comparable to the “bones” of negro minstrels, but without the
varying rhythm. As this performance is proceeding, the head and neck
are slowly moved through half a circle, till the tip of the beak
touches the ground, when the music ceases. As with the wing-snapping
just referred to, both sexes are equally skilful performers; but while
they seem to indulge in such exercises much more frequently, and with
more vim during the breeding season, they will break out after this
demonstrative fashion at all times of the year. But why, then, the need
for the yet more elaborate contrivances which are to be met with among
the Snipe, the Game-birds, and certain of the Passeres?
However, be this as it may, in a large number of species a special
mechanism has been evolved to produce sounds which, as has been
remarked, in other species are no less effectually made without that
mechanism.
One of the simplest of the cases is that furnished by the remarkable
“bleating” or “drumming” performances of many species of Snipe,
generally, if not only, when sexually excited, and especially of
the Common Snipe (_Gallinago cœlestis_) during its love-flights.
Mounting to a great height, this bird, at such times, suddenly turns,
and descends with prodigious speed, meanwhile holding the tail fully
expanded. The outermost pair of feathers are, however, specially
modified so that, in the first place, during this descent they stand
at right angles to the long axis of the body and well apart from the
rest of the tail-feathers. This alone, however, would not produce these
weird sounds, which owe their origin to the fact that these particular
feathers have their shafts conspicuously thickened and peculiarly
curved, while the vane or web of the inner side of the feather is
of great width and structurally differs from the vanes of the other
feathers, whereby the vane becomes more resistant to the rush of air
caused by the wings during the descent.
But in the case of these Snipe it is to be noted this curious form
of musical instrument is found in both sexes, and there is little
difference in the quality of the sounds produced, but the bleating of
the male is said to be the more resonant.
The Common Snipe is the best performer among several different species,
and it is to be noted presents, to a casual examination, no remarkable
or peculiar feature whatever—the structural differences just described
are only to be discovered by very patient scrutiny. But in the
Pin-tailed Snipe (_Gallinago stenura_) the number of the feathers has
been greatly increased, while at the same time their webs have been
so reduced that the outspread tail seems to consist of little more
than spines. With such a transformation one expects to find a quite
exceptional performance, far surpassing that of the Common Snipe. Yet
so far as observation and experiment go they effect absolutely nothing!
Here again we have a case where modification of structure has passed
the bounds of need and passed so far as to make the whole tail useless
as a sound-producing organ!
A contrast and a parallel are afforded by some of the gallinaceous
birds of South America. The Black Penelope (_Penelopina nigra_) of
Guatemala, while on the wing, will, during its “love-flights,” pitch
suddenly earthwards with outstretched wings, and at such times a
crashing, rushing sound is produced, which has been likened to the
sound of a falling tree. Yet there is nothing in the shape of the wing
which will account for this. On the other hand, a near relation of
this bird, the Black-wattled Guan, _Aburria_ (_Penelope_) _aburri_ has
the four outermost primaries deeply incised along their inner vanes,
reducing the outermost portion of the feathers to mere spines. Yet, so
far as is known, this wing makes no especial noise. However, the males
of certain little South American Perching-birds known as Manakins have
the shafts of the secondary quills thickened to an extraordinary degree
so as to form solid, horny lumps, and these, when the wings are brought
together smartly over the back, produce a noise not unlike the crack of
a whip, so that here again structure and function are found together.
In the contradictory cases just cited where specialized parts are found
which are apparently functionless, we must suppose that the habit of
using them has been supplanted by some new stimulant.
The part played by musical instruments of percussion would seem to
be a variable one. In some cases, and possibly in all, it may serve
as an excitant, or stimulant, to the rousing of a “sex-storm”; in
many, at any rate, such sounds serve as calls to the sexes when
separated. This much seems to be demonstrated in the case of certain
of the Woodpeckers, which in this matter differ conspicuously from
any other species yet referred to, in that they have developed no
special sound-producing mechanism, but make use of hollow trees which
serve them as drums, the beak being used as the drumstick. This is a
very noteworthy fact, for one would have supposed that here at any
rate, where the production of loud and far-reaching sounds is of
vital importance, the means would have been provided by some such
modification of the wing-feathers as we have already seen to obtain in
the case, for example, of the Manakins. More closely examined, however,
this apparent failure of the organism to produce its own mechanism
becomes less remarkable, for Woodpeckers are forest-dwellers and but
indifferent fliers; loud sounds produced by the rapid vibration of
the wings or tail, as in the case of the Snipe, in mid-air, are thus
impracticable, if not impossible, and sounds produced after the fashion
of the Manakins would not have sufficient carrying power.
One of the most skilled performers among the Woodpeckers is the Great
Spotted Woodpecker (_Dendrocofus major_), whose weird drumming once
heard will never be forgotten. These sounds are produced by blows
of the beak on a branch, delivered so rapidly that the bird’s head
presents but a blurred appearance. The sounds thus made vary with the
resonance of the wood and can be heard at a distance of half a mile.
These strange vibrating notes are most frequently heard during the
courting season, and they will commonly beget a speedy response from
some more or less distant part of the wood, so that their purpose is
clear. They attain the same end as the bellowing of the stag or the
“lek” of the Capercaillie. They are, however, to be heard at other
times, as when the birds are greatly alarmed or when the nest is being
robbed.