DOUBLE ANNUAL MOULT. 
83 
c«. 
At> ' Xlii. 
^ been acquired in order that the male should assume 
K,' 111 ? the breerlin^-season an ornamental character; 
ae llla l the double moult, having been originally 
I haired f 01 . some distinct purpose, has subsequently 
W-^en. advantage of in certain cases for gaining a 
J’ t!al Plumage. 
tli, + a ?P ears at first sight a surprising circumstance 
lad ' v ‘th closely-allied birds, some species should regu- 
s j ri ^ Undergo a double annual moult, and others only a 
0l , g 0 °ne. The ptarmigan, for instance, moults twice 
^ thrice in the year, and the black-cock only 
IXo S01ae of the splendidly-coloured honey-suckers 
eoi 0 ' tai 'inj©) of India and some sub-genera of obscurely- 
] lav ° Ure< i pipits (Anthus) have a double, whilst others 
d a f 6 ° nl y a single annual moult. 76 But the gra- 
<k'ci° nS - n tlle manner of moulting, which are known to 
gj. 0 r witl1 various birds, shew us how species, or whole 
do ,2 3 of species, might have originally acquired their 
l, aVp 6 ai >nual moult, or having once gained the habit, 
t] le !l 8 a in lost it. With certain bustards and plovers 
b 6 i Ii Verna l moult is far from complete, some feathers 
also' 8 1enewe d, and some changed in colour. There is 
r a il ,! ea8 °n to believe that with certain bustards and 
s 0U) 1 ' <J birds, which properly undergo a double moult, 
tlir,, 6 tlle °Uer males retain their nuptial plumage 
lUav" i ° nt the year. A few highly modified feathers 
a s (J l one be added during the spring to the plumage, 
O rS " bh the disc-formed tail-feathers of certain 
fe at]f,° S ffliringa) in India, and with the elongated 
By er ® 011 the back, neck, and crest of certain herons. 
c 1 steps as these, the vernal moult might be ren- 
Olq 
bnta| a > ^ 10 awaiting of tlie ptarmigan, see Gould’s ‘ Birds of Great 
3Gg v 1 honey-suckers, Jerdon, ‘ Birds of India,’ vol. i. p. 359, 
a the moulting of Anthus, see Blyth, in 1 Ibis,’ 1867, p. 32. 
G 2 
