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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2889 times)
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« Reply #135 on: February 09, 2009, 03:13:45 pm »

* The brown mottled summer plumage of the ptarmigan is of as much
importance to it, as a protection, as the white winter plumage; for in
Scandinavia during the spring, when the snow has disappeared, this
bird is known to suffer greatly from birds of prey, before it has
acquired its summer dress: see Wilhelm von Wright, in Lloyd, Game
Birds of Sweden, 1867, p. 125.
  *(2) In regard to the previous statements on moulting, see, on
snipes, &c., Macgillivray, Hist. Brit. Birds, vol. iv., p. 371; on
Glareolae, curlews, and bustards, Jerdon, Birds of India, vol. iii.,
pp. 615, 630, 683; on Totanus, ibid., p. 700; on the plumes of herons,
ibid., p. 738, and Macgillivray, vol. iv., pp. 435 and 444, and Mr.
Stafford Allen, in the Ibis, vol. v., 1863, p. 33.

  From the foregoing facts, more especially from neither sex of
certain birds changing colour during either annual moult, or
changing so slightly that the change can hardly be of any service to
them, and from the females of other species moulting twice yet
retaining the same colours throughout the year, we may conclude that
the habit of annually moulting twice has not been acquired in order
that the male should assume an ornamental character during the
breeding-season; but that the double moult, having been originally
acquired for some distinct purpose, has subsequently been taken
advantage of in certain cases for gaining a nuptial plumage.
  It appears at first sight a surprising circumstance that some
closely-allied species should regularly undergo a double annual moult,
and others only a single one. The ptarmigan, for instance, moults
twice or even thrice in the year, and the blackcock only once: some of
the splendidly coloured honey-suckers (Nectariniae) of India and
some sub-genera of obscurely coloured pipits (Anthus) have a double,
whilst others have only a single annual moult.* But the gradations
in the manner of moulting, which are known to occur with various
birds, shew us how species, or whole groups, might have originally
acquired their double annual moult, or having once gained the habit,
have again lost it. With certain bustards and plovers the vernal moult
is far from complete, some feathers being renewed, and some changed in
colour. There is also reason to believe that with certain bustards and
rail-like birds, which properly undergo a double moult, some of the
older males retain their nuptial plumage throughout the year. A few
highly modified feathers may merely be added during the spring to
the plumage, as occurs with the disc-formed tail-feathers of certain
drongos (Bhringa) in India, and with the elongated feathers on the
back, neck, and crest of certain herons. By such steps as these, the
vernal moult might be rendered more and more complete, until a perfect
double moult was acquired. Some of the birds of paradise retain
their nuptial feathers throughout the year, and thus have only a
single moult; others cast them directly after the breeding-season, and
thus have a double moult; and others again cast them at this season
during the first year, but not afterwards; so that these latter
species are intermediate in their manner of moulting. There is also
a great difference with many birds in the length of time during
which the two annual plumages are retained; so that the one might come
to be retained for the whole year, and the other completely lost. Thus
in the spring Machetes pugnax retains his ruff for barely two
months. In Natal the male widow-bird (Chera progne) acquires his
fine plumage and long tail-feathers in December or January, and
loses them in March; so that they are retained only for about three
months. Most species, which undergo a double moult, keep their
ornamental feathers for about six months. The male, however, of the
wild Gallus bankiva retains his neck-hackles for nine or ten months;
and when these are cast off, the underlying black feathers on the neck
are fully exposed to view. But with the domesticated descendant of
this species, the neck-hackles of the male are immediately replaced by
new ones; so that we here see, as to part of the plumage, a double
moult changed under domestication into a single moult.*(2)

  * On the moulting of the ptarmigan, see Gould's Birds of Great
Britain. On the honey-suckers, Jerdon, Birds of India, vol. i., pp.
359, 365, 369. On the moulting of Anthus, see Blyth, in Ibis, 1867, p.
  *(2) For the foregoing statements in regard to partial moults, and
on old males retaining their nuptial plumage, see Jerdon, on
bustards and plovers, in Birds of India, vol. iii., pp. 617, 637, 709,
711. Also Blyth in Land and Water, 1867, p. 84. On the moulting of
Paradisea, see an interesting article by Dr. W. Marshall, Archives
Neerlandaises, tom. vi., 1871. On the Vidua, Ibis, vol. iii., 1861, p.
133. On the Drongoshrikes, Perdon, ibid., vol. i., p. 435. On the
vernal moult of the Herodias bubulcus, Mr. S. S. Allen, in Ibis, 1863,
p. 33. On Gallus bankiva, Blyth, in Annals and Mag. of Natural
History, vol. i., 1848, p. 455; see, also, on this subject, my
Variation of Animals under Domestication, vol. i., p. 236.

  The common drake (Anas boschas), after the breeding-season, is
well known to lose his male plumage for a period of three months,
during which time he assumes that of the female. The male pin-tail
duck (Anas acuta) loses his plumage for the shorter period of six
weeks or two months; and Montagu remarks that "this double moult
within so short a time is a most extraordinary circumstance, that
seems to bid defiance to all human reasoning." But the believer in the
gradual modification of species will be far from feeling surprise at
finding gradations of all kinds. If the male pin-tail were to
acquire his new plumage within a still shorter period, the new male
feathers would almost necessarily be mingled with the old, and both
with some proper to the female; and this apparently is the case with
the male of a not distantly-allied bird, namely the Merganser
serrator, for the males are said to "undergo a change of plumage,
which assimilates them in some measure to the female." By a little
further acceleration in the process, the double moult would be
completely lost.*

  * See Macgillivray, Hist. British Birds (vol. v., pp. 34, 70, and
223), on the moulting of the Anatidae, with quotations from Waterton
and Montagu. Also Yarrell, History of British Birds, vol. iii., p.

  Some male birds, as before stated, become more brightly coloured
in the spring, not by a vernal moult, but either by an actual change
of colour in the feathers, or by their obscurely-coloured deciduary
margins being shed. Changes of colour thus caused may last for a
longer or shorter time. In the Pelecanus onocrotalus a beautiful
rosy tint, with lemon-coloured marks on the breast, overspreads the
whole plumage in the spring; but these tints, as Mr. Sclater states,
"do not last long, disappearing generally in about six weeks or two
months after they have been attained." Certain finches shed the
margins of their feathers in the spring, and then become brighter
coloured, while other finches undergo no such change. Thus the
Fringilla tristis of the United States (as well as many other American
species) exhibits its bright colours only when the winter is past,
whilst our goldfinch, which exactly represents this bird in habits,
and our siskin, which represents it still more closely in structure,
undergo no such annual change. But a difference of this kind in the
plumage of allied species is not surprising, for with the common
linnet, which belongs to the same family, the crimson forehead and
breast are displayed only during the summer in England, whilst in
Madeira these colours are retained throughout the year.*

  * On the pelican, see Sclater, in Proc. Zool. Soc., 1868, p. 265. On
the American finches, see Audubon, Ornithological Biography, vol.
i., pp. 174, 221, and Jerdon, Birds of India, vol. ii., p. 383. On the
Fringilla cannabina of Madeira, Mr. E. Vernon Harcourt, Ibis, vol. v.,
1863, p. 230.

  Display by Male Birds of their Plumage.- Ornaments of all kinds,
whether permanently or temporarily gained, are sedulously displayed by
the males, and apparently serve to excite, attract, or fascinate the
females. But the males will sometimes display their ornaments, when
not in the presence of the females, as occasionally occurs with grouse
at their balz-places, and as may be noticed with the peacock; this
latter bird, however, evidently wishes for a spectator of some kind,
and, as I have often seen, will show off his finery before poultry, or
even pigs.* All naturalists who have closely attended to the habits of
birds, whether in a state of nature or under confinement, are
unanimously of opinion that the males take delight in displaying their
beauty. Audubon frequently speaks of the male as endeavouring in
various ways to charm the female. Mr. Gould, after describing some
peculiarities in a male humming-bird, says he has no doubt that it has
the power of displaying them to the greatest advantage before the
female. Dr. Jerdon*(2) insists that the beautiful plumage of the
male serves "to fascinate and attract the female." Mr. Bartlett, at
the Zoological Gardens, expressed himself to me in the strongest terms
to the same effect.
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