that the summer plumage, though common to both sexes, partakes of the
nature of the exclusively masculine plumage of many other birds. (80.
In regard to the previous statements on moulting, see, on snipes, etc.,
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. (81. 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. 32.) 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
414