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Descent of Man [ 1871]

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Bullseye
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« Reply #120 on: February 09, 2009, 03:11:23 pm »

Chapter XIII - Secondary Sexual Characters of Birds

  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,* 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) 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 shown 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.

  * Ibis., vol. iii. (new series), 1867, p. 414.
  *(2) Gould, Handbook of the Birds of Australia, 1865, vol. ii., p.
383.

  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* 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."*(2) 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.*(3) 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."*(4)

  * Quoted by Mr. Gould, Introduction to the Trochilidae, 1861, page
29.
  *(2) Gould, ibid., p. 52.
  *(3) W. Thompson, Natural History of Ireland: Birds, vol. ii., 1850,
p. 327.
  *(4) Jerdon, Birds of India, 1863, vol. ii., p. 96.

  The polygamous ruff (see 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.* 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."*(2) 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."*(3)

  * Macgillivray, History of British Birds, vol. iv., 1852, pp.
177-181.
  *(2) Sir R. Schomburgk, in Journal of Royal Geographic Society, vol.
xiii., 1843, p. 31.
  *(3) Ornithological Biography, vol. i., p. 191. For pelicans and
snipes, see vol. iii., pp. 138, 477.

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