€hap. XIII. 
DOUBLE ANNUAL MOULT. 
83 
not been acquired in order that tbe male should assume 
during the breeding-season an ornamental character; 
but that the double moult, having been originally 
acquired for some distinct purpose, has subsequently 
been taken advantage of in certain eases for gaining a 
nuptial plumage. 
It appears at first sight a surprising circumstance 
that with closely-allied birds, some species should regu- 
larly 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 black-cock only 
once : some of the splendidly-coloured honey-suckers 
{Nectarinim) of India and some sub-genera of obscurely- 
eoloured pipits (Anthus) have a double, whilst others 
have only a single annual moult.'^® But the gra- 
dations in the manner of moulting, which are known to 
occur with various birds, shew us how species, or whole 
groups of species, might have originally acquired their 
double annual moult, or having once gained the habit, 
have again lost it. With certain bustards and plovers 
Ihe 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 alone be added during the spring to the plumage, 
as occurs with the disc-formed tail-feathers of certain 
drongos (Bhringd) 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 ren- 
On the moulting of the ptarmigan, see Gould’s ‘ Birds of Great 
Britain.’ On the honey-suckers, Jerdon, ^ Birds of India,’ vol. i. p. 359, 
^65, 369. On the moulting of Anthus, see Blyth, in ‘ Ibis,’ 1867, 32, 
G- 2 
