302 Tlie Descent of Man. Pabt 11. 



moult, and others only a single one. The ptarmigan, for 

 inBtance, moults twice or even thrice in the year, and the black- 

 cock only once : some of the splendidly coloured honey-suckers 

 (Nectarinise) 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 under- 

 go 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 tliroughout 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 bii'ds in the length of time during which the two annual 

 plumages are retained ; so that the one might come to be re- 

 tained for the whole year, and the other completely lost. Thus 

 in the spring MucJii-tis pvgnax 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 Match; 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 Oallua hankiva 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 



" On the moulting of the pt.ir- 359, 365, 369. On the moulting ol 



niigjin, sie Gould's 'Birds of Grciit Antlius, see Blyth, in 'Ibis,' 186'f, 



liritiiin.* On tlii hnncy-vuckors, p. 32. 

 Jerdoii, ' birds of IndiH,' vol. i. pp. 



