|
Bullseye
|
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 plumes which spring
from beneath the wings of the Paradisea apoda, when vertically erected
and made to vibrate, are described as forming a sort of halo, in the
centre of which the head "looks like a little emerald sun with its
rays formed by the two plumes."* In another most beautiful species the
head is bald, "and of a rich cobalt blue, crossed by several lines
of black velvety feathers."*(2)
* Quoted from M. de Lafresnaye in Annals and Mag. of Natural
History, vol. xiii., 1854, p. 157: see also Mr. Wallace's much
fuller account in vol. xx., 1857, p. 412, and in his The Malay
Archipelago.
*(2) Wallace, The Malay Archipelago, vol. ii., 1869, p. 405.
Male humming-birds (see figs. 48 and 49) almost vie with birds of
paradise in their beauty, as every one will admit who has seen Mr.
Gould's splendid volumes, or his rich collection. It is very
remarkable in how many different ways these birds are ornamented.
Almost every part of their plumage has been taken advantage of, and
modified; and the modifications have been carried, as Mr. Gould shewed
me, to a wonderful extreme in some species belonging to nearly every
sub-group. Such cases are curiously like those which we see in our
fancy breeds, reared by man for the sake of ornament; certain
individuals originally varied in one character, and other
individuals of the same species in other characters; and these have
been seized on by man and much augmented- as shewn by the tail of
the fantail-pigeon, the hood of the jacobin, the beak and wattle of
the carrier, and so forth. The sole difference between these cases
is that in the one, the result is due to man's selection, whilst in
the other, as with humming-birds, birds of paradise, &c., it is due to
the selection by the females of the more beautiful males.
I will mention only one other bird, remarkable from the extreme
contrast in colour between the sexes, namely the famous bell-bird
(Chasmorhynchus niveus) of S. America, the note of which can be
distinguished at the distance of nearly three miles, and astonishes
every one when first hearing it. The male is pure white, whilst the
female is dusky-green; and white is a very rare colour in
terrestrial species of moderate size and inoffensive habits. The male,
also, as described by Waterton, has a spiral tube, nearly three inches
in length, which rises from the base of the beak. It is jet-black,
dotted over with minute downy feathers. This tube can be inflated with
air, through a communication with the palate; and when not inflated
hangs down on one side. The genus consists of four species, the
males of which are very distinct, whilst the females, as described
by Mr. Sclater in a very interesting paper, closely resemble each
other, thus offering an excellent instance of the common rule that
within the same group the males differ much more from each other
than do the females. In a second species (C. nudicollis) the male is
likewise snow-white, with the exception of a large space of naked skin
on the throat and round the eyes, which during the breeding-season
is of a fine green colour. In a third species (C. tricarunculatus) the
head and neck alone of the male are white, the rest of the body
being chestnut-brown, and the male of this species is provided with
three filamentous projections half as long as the body- one rising
from the base of the beak, and the two others from the corners of
the mouth.*
* Mr. Sclater, Intellectual Observer, Jan., 1867. Waterton's
Wanderings, p. 118. See also Mr. Salvin's interesting paper, with a
plate, in the Ibis, 1865, p. 90.
The coloured plumage and certain other ornaments of the adult
males are either retained for life, or are periodically renewed during
the summer and breeding-season. At this same season the beak and naked
skin about the head frequently change colour, as with some herons,
ibises, gulls, one of the bell-birds just noticed, &c. In the white
ibis, the cheeks, the inflatable skin of the throat, and the basal
portion of the beak then become crimson.* In one of the rails,
Gallicrex cristatus, a large red caruncle is developed during this
period on the head of the male. So it is with a thin **** crest on
the beak of one of the pelicans, P. erythrorhynchus; for, after the
breeding-season, these **** crests are shed, like horns from the
heads of stags, and the shore of an island in a lake in Nevada was
found covered with these curious exuviae.*(2)
* Land and Water, 1867, p. 394.
*(2) Mr. D. G. Elliot, in Proc. Zool. Soc., 1869, p. 589.
Changes of colour in the plumage according to the season depend,
firstly on a double annual moult, secondly on an actual change of
colour in the feathers themselves, and thirdly on their
dull-coloured margins being periodically shed, or on these three
processes more or less combined. The shedding of the deciduary margins
may be compared with the shedding of their down by very young birds;
for the down in most cases arises from the summits of the first true
feathers.*
* Nitzsch's "Pterylography," edited by P. L. Sclater, Ray Society,
1867, p. 14.
With respect to the birds which annually undergo a double moult,
there are, firstly, some kinds, for instance snipes, swallow-plovers
(Glareolae), and curlews, in which the two sexes resemble each
other, and do not change colour at any season. I do not know whether
the winter plumage is thicker and warmer than the summer plumage,
but warmth seems the most probable end attained of a double moult,
where there is no change of colour. Secondly, there are birds, for
instance, certain species of Totanus and other Grallatores, the
sexes of which resemble each other, but in which the summer and winter
plumage differ slightly in colour. The difference, however, in these
cases is so small that it can hardly be an advantage to them; and it
may, perhaps, be attributed to the direct action of the different
conditions to which the birds are exposed during the two seasons.
Thirdly, there are many other birds the sexes of which are alike,
but which are widely different in their summer and winter plumage.
Fourthly, there are birds the sexes of which differ from each other in
colour; but the females, though moulting twice, retain the same
colours throughout the year, whilst the males undergo a change of
colour, sometimes a great one, as with certain bustards. Fifthly and
lastly, there are birds the sexes of which differ from each other each
other in both their summer and winter plumage; but the male
undergoes a greater amount of change at each recurrent season than the
female of which the ruff (Machetes pugnax) offers a good instance.
With respect to the cause or purpose of the differences in colour
between the summer and winter plumage, this may in some instances,
as with the ptarmigan,* serve during both seasons as a protection.
When the difference between the two plumages is slight it may
perhaps be attributed, as already remarked, to the direct action of
the conditions of life. But with many birds there can hardly be a
doubt that the summer plumage is ornamental, even when both sexes
are alike. We may conclude that this is the case with many herons,
egrets, &c., for they acquire their beautiful plumes only during the
breeding-season. Moreover, such plumes, top-knots, &c., though
possessed by both sexes, are occasionally a little more developed in
the male than in the female; and they resemble the plumes and
ornaments possessed by the males alone of other birds. It is also
known that confinement, by affecting the reproductive system of male
birds, frequently checks the development of their secondary sexual
characters, but has no immediate influence on any other characters;
and I am informed by Mr. Bartlett that eight or nine specimens of
the knot (Tringa canutus) retained their unadorned winter plumage in
the Zoological Gardens throughout the year, from which fact we may
infer that the summer plumage, though common to both sexes, partakes
of the nature of the exclusively masculine plumage of many other
birds.*(2)
|
