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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 female by vocal or
instrumental music of the most varied kinds. They are ornamented by all
sorts of combs, wattles, protuberances, horns, air-distended sacks, 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 (1. 'Ibis,' vol. iii. (new series), 1867, p. 414.),
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. (2. Gould, 'Handbook of the Birds of
Australia,' 1865, vol. ii. p. 383.) 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. In man, however, when cultivated, the sense of beauty is manifestly
a far more complex feeling, and is associated with various intellectual
ideas.
Before treating of the sexual 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 male and female 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 Neomorpha of New Zealand, there is, as we have seen,
a still wider difference in the form of the beak in relation to the manner
of feeding of the two sexes. Something of the same kind has been observed
with the 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 are often 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 kind as a foundation, we
can see how the beaks of the two sexes might be made to differ greatly
through natural selection. In some of the above cases, however, it is
possible that the beaks of the males may have been first modified in
relation to their contests with other males; and that this 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 (3. Quoted by Mr. Gould, 'Introduction
to the Trochilidae,' 1861, page 29.) describes a battle in which a pair
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 or another
genus of humming-bird, 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." (4. Gould, ibid. p. 52.) 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. (5. W. Thompson, 'Natural History of Ireland:
Birds,' vol. ii. 1850, p. 327.) Mr. Blyth informs me that the males of an
allied bird (Gallicrex cristatus) are a 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 hoemorrhous) which "fight with great spirit." (6. Jerdon,
'Birds of India,' 1863, vol. ii. p. 96.)
[Fig. 37. The Ruff or Machetes pugnax (from Brehm's 'Thierleben').]
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. (7. Macgillivray, 'History of British Birds,'
vol. iv. 1852, pp. 177-181.) 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." (8. Sir R. Schomburgk, in 'Journal of Royal Geographic
Society,' vol. xiii. 1843, p. 31.) Birds which seem ill-adapted for
fighting engage in fierce conflicts; thus the stronger males of the pelican
drive away the weaker ones, snapping with their huge beaks and giving heavy
blows with their wings. Male snipe fight together, "tugging and pushing
each other with their bills in the most curious manner imaginable." Some
few birds are believed never to fight; this is the case, according to
Audubon, with one of the woodpeckers of the United States (Picu sauratus),
although "the hens are followed by even half a dozen of their gay suitors."
(9. 'Ornithological Biography,' vol. i. p. 191. For pelicans and snipes,
see vol. iii. pp. 138, 477.)
The males of many birds are larger than the females, and this no doubt is
the result of the advantage gained by the larger and stronger males over
their rivals during many generations. 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. (10. Gould, 'Handbook of Birds of Australia,' vol. i.
p. 395; vol. ii. p. 383.) 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 (11. Mr. Hewitt, in the 'Poultry Book' by Tegetmeier,
1866, p. 137.) 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 brutal scene,
told me that a bird had both its legs broken by some accident in the
cockpit, 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, 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. (12.
Layard, 'Annals and Magazine of Natural History,' vol. xiv. 1854, p. 63.)
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." (13. Jerdon,
'Birds of India,' vol. iii. p. 574.)
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. Dr. W. Kovalevsky 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-dances and love-songs of
the Black-cock are called in Germany. The bird utters almost continuously
the strangest 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. (14. Brehm, 'Thierleben,' 1867, B. iv.
s. 351. Some of the foregoing statements are taken from L. Lloyd, 'The
Game Birds of Sweden,' etc., 1867, p. 79.)
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 at some little distance from Chester two peacocks became so
excited whilst fighting, that they flew over the whole city, still engaged,
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 (Fig. 51) 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 erythrophthalmus) 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. (15. Jerdon, 'Birds of India': on Ithaginis, vol. iii. p.
523; on Galloperdix, p. 541.) Hence spurs may be considered as a masculine
structure, which has been occasionally more or less transferred to the
females. Like most other secondary sexual characters, the spurs are highly
variable, both in number and development, in the same species.
[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
species. 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 been known to drive 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. (16. For the Egyptian
goose, see Macgillivray, 'British Birds,' vol. iv. p. 639. For
Plectropterus, Livingstone's 'Travels,' p. 254. For Palamedea, Brehm's
'Thierleben,' B. iv. s. 740. See also on this bird Azara, 'Voyages dans
l'Amerique merid.' tom. iv. 1809, pp. 179, 253.) 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 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 fatal results. Thus also they drive
away other enemies. (17. See, on our peewit, Mr. R. Carr in 'Land and
Water,' Aug. 8th, 1868, p. 46. In regard to Lobivanellus, see Jerdon's
'Birds of India,' vol. iii. p. 647, and Gould's 'Handbook of Birds of
Australia,' vol. ii. p. 220. For the Hoplopterus, see Mr. Allen in the
'Ibis,' vol. v. 1863, p. 156.)
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 (18. Audubon, 'Ornithological Biography,' vol. ii. p. 492; vol. i.
pp. 4-13.), 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. (19. Mr. Blyth, 'Land and Water,' 1867, p. 212.) 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
(20. Richardson on Tetrao umbellus, 'Fauna Bor. Amer.: Birds,' 1831, p.
343. L. Lloyd, 'Game Birds of Sweden,' 1867, pp. 22, 79, on the
capercailzie and black-cock. Brehm, however, asserts ('Thierleben,' B. iv.
s. 352) that in Germany the grey-hens do not generally attend the Balzen of
the black-cocks, but this is an exception to the common rule; possibly the
hens may lie hidden in the surrounding bushes, as is known to be the case
with the gray-hens in Scandinavia, and with other species in N. America.),
which afterwards pair with the victorious combatants. But in some cases
the pairing precedes instead of succeeding the combat: thus according to
Audubon (21. 'Ornithological Biography,' vol. ii. p. 275.), several males
of the Virginian goat-sucker (Caprimulgus virgianus) "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 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 Dr. W.
Kovalevsky 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.
(22. Brehm, 'Thierleben,' etc., B. iv. 1867, p. 990. Audubon,
'Ornithological Biography,' vol. ii. p. 492.)
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 (23. 'Land and Water,' July 25, 1868, p. 14.)
goes so far as to believe that the battles of the male "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." (24. Audubon's 'Ornithological Biography;' on
Tetrao cupido, vol. ii. p. 492; on the Sturnus, vol. ii. p. 219.)
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 in the case of the hissing noise made by some
nestling-birds. Audubon (25. 'Ornithological Biography,' vol. v. p.
601.), 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" (26. The Hon. Daines Barrington,
'Philosophical Transactions,' 1773, p. 252.); 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 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
armorous notes, which, by instinct, the female knows, and repairs to the
spot to choose her mate." (27. 'Ornithological Dictionary,' 1833, p.
475.) 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." (28. 'Naturgeschichte der Stubenvogel,' 1840, s. 4.
Mr. Harrison Weir likewise writes to me:--"I am informed that the best
singing males generally get a mate first, when they are bred in the same
room.") 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. (29. 'Philosophical
Transactions,' 1773, p. 263. White's 'Natural History of Selborne,' 1825,
vol. i. p. 246.) 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
(30. 'Naturgesch. der Stubenvogel,' 1840, s. 252.), 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 (31. Mr. Bold, 'Zoologist,'
1843-44, p. 659.) 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, as Mr. Weir informs me, a man has in the
course of a single day caught 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 male birds should sing from emulation as well as for charming the
female, is not at all incompatible; and it might have been expected that
these two habits would have concurred, like those of display 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 of the
canary, robin, lark, and bullfinch, especially when in a state of
widowhood, as Bechstein remarks, 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 (32. D. Barrington,
'Philosophical Transactions,' 1773, p. 262. Bechstein, 'Stubenvogel,'
1840, s. 4.), for this disturbs all the 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. (33. This is likewise the
case with the water-ouzel; see Mr. Hepburn in the 'Zoologist,' 1845-46, p.
1068.) 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 Balzen or leks at the usual place of
assemblage during the autumn. (34. L. Lloyd, 'Game Birds of Sweden,'
1867, p. 25.) Hence it is not at all surprising that male birds should
continue singing for their own amusement after the season for courtship is
over.
As shewn in a previous chapter, singing is to a certain extent 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 (35. Barrington, ibid. p. 264, Bechstein,
ibid. s. 5.), and sometimes that of their neighbours. (36. Dureau de la
Malle gives a curious instance ('Annales des Sc. Nat.' 3rd series, Zoolog.,
tom. x. p. 118) of some wild blackbirds in his garden in Paris, which
naturally learnt a republican air from a caged bird.) 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 (37. Bishop, in 'Todd's Cyclopaedia of Anatomy and
Physiology,' vol. iv. p. 1496.), though they never sing, and do not
naturally modulate their voices to any great extent. Hunter asserts (38.
As stated by Barrington in 'Philosophical Transactions,' 1773, p. 262.)
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. (39. Gould, 'Handbook to
the Birds of Australia,' vol. i. 1865, pp. 308-310. See also Mr. T.W. Wood
in the 'Student,' April 1870, p. 125.) It is also remarkable that birds
which sing well 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, etc., utter harsh cries; and the brilliant birds of
the tropics are hardly ever songsters. (40. See remarks to this effect in
Gould's 'Introduction to the Trochilidae,' 1861, p. 22.) 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 be employed to charm the
females; and melody of voice offers one such means.
[Fig. 39. Tetrao cupido: male. (T.W. Wood.)]
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 his 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." (41. 'The Sportsman and Naturalist in Canada,' by
Major W. Ross King, 1866, pp. 144-146. Mr. T.W. Wood gives in the
'Student' (April 1870, p. 116) an excellent account of the attitude and
habits of this bird during its courtship. He states that the ear-tufts or
neck-plumes are erected, so that they meet over the crown of the head. See
his drawing, Fig. 39.) 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. (42.
Richardson, 'Fauna Bor. American: Birds,' 1831, p. 359. Audubon, ibid.
vol. iv. p. 507.)
[Fig. 40. The Umbrella-bird or Cephalopterus ornatus, male (from Brehm).]
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, as was
formerly supposed, serve to hold water, but is connected with the utterance
during the breeding-season of a peculiar sound resembling "oak." (43. The
following papers have been lately written on this subject: Prof. A.
Newton, in the 'Ibis,' 1862, p. 107; Dr. Cullen, ibid. 1865, p. 145; Mr.
Flower, in 'Proc. Zool. Soc.' 1865, p. 747; and Dr. Murie, in 'Proc. Zool.
Soc.' 1868, p. 471. In this latter paper an excellent figure is given of
the male Australian Bustard in full display with the sack distended. It is
a singular fact that the sack is not developed in all the males of the same
species.) A crow-like bird inhabiting South America (see 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. (44. Bates, 'The
Naturalist on the Amazons,' 1863, vol. ii. p. 284; Wallace, in
'Proceedings, Zoological Society,' 1850, p. 206. A new species, with a
still larger neck-appendage (C. penduliger), has lately been discovered,
see 'Ibis,' vol. i. p. 457.)
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 adult female or young male. In the male
Merganser the enlarged portion of the trachea is furnished with an
additional pair of muscles. (45. Bishop, in Todd's 'Cyclopaedia of
Anatomy and Physiology,' vol. iv. p. 1499.) In one of the ducks, however,
namely Anas punctata, the bony enlargement is only a little more developed
in the male than in the female. (46. Prof. Newton, 'Proc. Zoolog. Soc.'
1871, p. 651.) But the meaning of these differences in the trachea of the
two sexes of the Anatidae is not 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. (47. The spoonbill (Platalea) has its trachea
convoluted into a figure of eight, and yet this bird (Jerdon, 'Birds of
India,' vol. iii. p. 763) is mute; but Mr. Blyth informs me that the
convolutions are not constantly present, so that perhaps they are now
tending towards abortion.) 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. (48.
'Elements of Comparative Anatomy,' by R. Wagner, Eng. translat. 1845, p.
111. With respect to the swan, as given above, Yarrell's 'History of
British Birds,' 2nd edition, 1845, vol. iii. p. 193.) Highly important
structures have, therefore, 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 note
which differs from the gobbling noise made, when with erected feathers,
rustling wings and distended wattles, he puffs and struts before her. (49.
C.L. Bonaparte, quoted in the 'Naturalist Library: Birds,' vol. xiv. p.
126.) 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 present are
thus charmed. (50. L. Lloyd, 'The Game Birds of Sweden,' etc., 1867, pp.
22, 81.) The voice of the common rook is known to alter during the
breeding-season, and is therefore in some way sexual. (51. Jenner,
'Philosophical Transactions,' 1824, p. 20.) 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 without any advantage being thus gained, the loud
voices of many male birds may be the result of the inherited effects of the
continued use of their vocal organs when 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. 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 by rapidly
striking his wings together above his back, according to Mr. R. Haymond,
and not, as Audubon thought, by striking them against his sides. 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." The male of the Kalij-pheasant, in
the Himalayas, 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 season, and at no other time,
the males of certain night-jars (Caprimulgus) make a strange booming 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 source would never be conjectured by any one hearing 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 observed, 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." If the beak is not thus struck
against some object, the sound is quite different. Air is at the same time
swallowed, and the oesophagus thus becomes much swollen; and this probably
acts as a resonator, not only with the hoopoe, but with pigeons and other
birds. (52. For the foregoing facts see, on Birds of Paradise, Brehm,
'Thierleben,' Band iii. s. 325. On Grouse, Richardson, 'Fauna Bor.
Americ.: Birds,' pp. 343 and 359; Major W. Ross King, 'The Sportsman in
Canada,' 1866, p. 156; Mr. Haymond, in Prof. Cox's 'Geol. Survey of
Indiana,' p. 227; Audubon, 'American Ornitholog. Biograph.' vol. i. p. 216.
On the Kalij-pheasant, Jerdon, 'Birds of India,' vol. iii. p. 533. On the
Weavers, Livingstone's 'Expedition to the Zambesi,' 1865, p. 425. On
Woodpeckers, Macgillivray, 'Hist. of British Birds,' vol. iii. 1840, pp.
84, 88, 89, and 95. On the Hoopoe, Mr. Swinhoe, in 'Proc. Zoolog. Soc.'
June 23, 1863 and 1871, p. 348. On the Night-jar, Audubon, ibid. vol. ii.
p. 255, and 'American Naturalist,' 1873, p. 672. The English Night-jar
likewise makes in the spring a curious noise during its rapid flight.)
[Fig. 41. Outer tail-feather of Scolopax gallinago (from 'Proc. Zool.
Soc.' 1858).
Fig. 42. Outer tail-feather of Scolopax frenata.
Fig. 43. Outer tail-feather of Scolopax javensis.]
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
sounds. The drumming, bleating, neighing, or thundering noise (as
expressed by different observers) 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 to the earth in a curved
line, with outspread tail and quivering pinions, and surprising velocity.
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 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. (53. See M.
Meves' interesting paper in 'Proc. Zool. Soc.' 1858, p. 199. For the
habits of the snipe, Macgillivray, 'History of British Birds,' vol. iv. p.
371. For the American snipe, Capt. Blakiston, 'Ibis,' vol. v. 1863, p.
131.)
[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.]
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. (54. Mr. Salvin, in 'Proceedings, Zoological Society,'
1867, p. 160. I am much indebted to this distinguished ornithologist for
sketches of the feathers of the Chamaepetes, and for other information.)
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. (55. Jerdon,
'Birds of India,' vol. iii. pp. 618, 621.) In a widely different group of
birds, namely 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), thus excised. Whilst flying from flower to flower he makes "a
shrill, almost whistling noise" (56. Gould, 'Introduction to the
Trochilidae,' 1861, p. 49. Salvin, 'Proceedings, Zoological Society,'
1867, p. 160.); but it did not appear to Mr. Salvin that the noise was
intentionally made.
[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.]
Lastly, in several species of a sub-genus of Pipra or Manakin, the males,
as described by Mr. Sclater, have their SECONDARY wing-feathers modified 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." (57. Sclater, in 'Proceedings, Zoological Society,'
1860, p. 90, and in 'Ibis,' vol. iv. 1862, p. 175. Also Salvin, in 'Ibis,'
1860, p. 37.)
The diversity of the sounds, both vocal and instrumental, made by the males
of many birds 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 conclusion
arrived at as 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. In the case
of the modified feathers, by which the drumming, whistling, or roaring
noises are produced, we know 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 of 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 (58. 'The Nile
Tributaries of Abyssinia,' 1867, p. 203.), 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 some birds 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, 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. (59. For Tetrao
phasianellus, see Richardson, 'Fauna, Bor. America,' p. 361, and for
further particulars Capt. Blakiston, 'Ibis,' 1863, p. 125. For the
Cathartes and Ardea, Audubon, 'Ornithological Biography,' vol. ii. p. 51,
and vol. iii. p. 89. On the White-throat, Macgillivray, 'History of
British Birds,' vol. ii. p. 354. On the Indian Bustard, Jerdon, 'Birds of
India,' vol. iii. p. 618.)
[Fig. 46. Bower-bird, Chlamydera maculata, with bower (from Brehm).]
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 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 (60. Gould,
'Handbook to the Birds of Australia,' vol. i. pp. 444, 449, 455. The bower
of the Satin Bower-bird may be seen in the Zoological Society's Gardens,
Regent's Park.) the habits of some Satin Bower-birds which he kept in an
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 bead; he continues opening first one wing 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 assemblage, 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.
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. (61. See remarks to this effect, on the
'Feeling of Beauty among Animals,' by Mr. J. Shaw, in the 'Athenaeum,' Nov.
24th, 1866, p. 681.) 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 (Fig. 39) are occasionally present. The head
is sometimes covered with velvety down, as with the pheasant; or is naked
and vividly coloured. The throat, also, is sometimes ornamented with a
beard, 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 vivid tints, as in 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. (62. See Dr.
Murie's account with coloured figures in 'Proceedings, Zoological Society,'
1872, p. 730.) 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." (63. Mr. Monteiro,
'Ibis,' vol. iv. 1862, p. 339.) 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." (64. 'Land
and Water,' 1868, p. 217.)
The head, again, often supports fleshy appendages, filaments, and solid
protuberances. These, if not common to both sexes, are always confined to
the males. The solid protuberances have been described in detail by Dr. W.
Marshall (65. 'Ueber die Schadelhocker,' etc., 'Niederland. Archiv. fur
Zoologie,' B. I. Heft 2, 1872.), who shews that they are formed either of
cancellated bone coated with skin, or of dermal and other tissues. With
mammals true horns are always supported on the frontal bones, but with
birds various bones have been modified for this purpose; and in species of
the same group the protuberances may have cores of bone, or be quite
destitute of them, with intermediate gradations connecting these two
extremes. Hence, as Dr. Marshall justly remarks, variations of the most
different kinds have served for the development through sexual selection of
these ornamental appendages. Elongated feathers or plumes spring 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 itself of the Argus pheasant. With the peacock
even the bones of the tail have been modified to support the heavy tail-
coverts. (66. Dr. W. Marshall, 'Uber den Vogelschwanz,' ibid. B. I. Heft
2, 1872.) The body of the Argus 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 (67. Jardine's 'Naturalist Library: Birds,'
vol. xiv. p. 166.), and that of the beautifully ocellated secondary wing-
feathers nearly three feet. In a small African night-jar (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 night-jars, the
shafts of the elongated wing-feathers are naked, except at the extremity,
where there is a disc. (68. Sclater, in the 'Ibis,' vol. vi. 1864, p.
114; Livingstone, 'Expedition to the Zambesi,' 1865, p. 66.) Again, in
another genus of night-jars, the tail-feathers are even still more
prodigiously developed. In general the feathers of the tail are more often
elongated than those of the wings, as any great elongation of the latter
impedes flight. We thus see that in closely-allied birds ornaments of the
same kind have been gained by the males through the development of widely
different feathers.
It is a curious fact that the feathers of species belonging to very
distinct groups have been modified in almost exactly the same peculiar
manner. Thus the wing-feathers in one of the above-mentioned night-jars
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 king-fisher, 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.
(69. Jerdon, 'Birds of India,' vol. iii. p. 620.) It is a most singular
fact that the motmots, as Mr. Salvin has clearly shewn (70. 'Proceedings,
Zoological Society,' 1873, p. 429.), give to their tail feathers the
racket-shape by biting off the barbs, and, further, that this continued
mutilation has produced a certain amount of inherited effect.
[Fig. 47. Paradisea Papuana (T.W. Wood).]
Again, 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
from end to end; and these in the tail of the Paradisea apoda attain a
length of thirty-four inches (71. Wallace, in 'Annals and Magazine of
Natural History,' vol. xx. 1857, p. 416, and in his 'Malay Archipelago,'
vol. ii. 1869, p. 390.): in P. Papuana (Fig. 47) they are much shorter and
thin. 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 somewhat resembled 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. (72. See my work on
'The Variation of Animals and Plants under Domestication,' vol. i. pp. 289,
293.)
In regard to colour, hardly anything need here be said, for every one knows
how splendid are the tints of many 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
difference between the sexes 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 different ways that they must be
seen to be appreciated. The elongated and golden-orange plume
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