SEXUAL SELECTION 507 



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 throughout 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 

 afterward; so that these latter species are intermediate in 

 their manner of moulting. There is also a great difference 

 with many birds in the length of time during which the 

 two annual plumages are retained; so that the one might 

 come to be retained for the whole year, and the other com- 

 pletely lost. Thus in the spring Machetes pugnax retains 

 his ruff for barely two months. In Natal the male widow- 

 bird {Ghera progne) acquires his fine plumage and long tail- 

 feathers in December or January, and loses them in March; 

 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 Grallus 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 that 

 we here see, as to part of the plumage, a double moult 

 changed under domestication into a single moult." 



The common drake {Anas boschas) after the breeding 

 season is well known^ to lose his male plumage for a period 

 of three months, during which time he assumes that of the 



^ For the foregoing statements in regard to partial moults, and on old males 

 retaining their nuptial plumage, see Jerdon, on bustards and plovers, in "Birds 

 of India," vol. iii. pp. 61t, 631, 109, 711. Also Blyth in "Land and Water," 

 1867, p. 84. On the moulting of Paradiaea, see an interesting article by 

 Dr. W. Marshall, "Archives Neerlandaises," torn, vi., 1871. On the Vidua, 

 "Ibis," vol. iii., 1861, p. 133. On the Drongo-shrikes, Jerdon, ibid., vol. i. 

 p. 435. On the vernal moult of the BeroMas bubiilcm, Mr. S. S. AUeu, in 

 "Ibis," 1863, p. 33. On GfaOus banJciva, Blyth, in "Annals and Mag. of Nat 

 Hist.," vol. i., 1848, p. 456; see, also, on this subject, my "Variation of Ani- 

 mals under Domestication," vol. i. p. 236. 



