80 SEXUAL SELECTION : BIRDS. [Paut II. 



originally acquired tlu-ir doiil>k' iiiinual moult, or, having 

 once gained the habit, liave again lost it. With certain 

 bustards and i)lovers the vernal moult is far from com- 

 plete, some feathers being renewed, and some changed in 

 color. There is also reason to believe that with certain 

 bustards and rail-like birds, which properly imdergo a 

 double moult, some of the older males retain their nup- 

 tial plumage throughout the year. A few liighly-modified 

 feathers may alone be added during the spring to the 

 phunage, as occurs with the disk-fox-raed tail-feathers of 

 certain drongos {Bhringa) in India, and ^^dth the elon- 

 gated 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. A gradation can also be 

 shown to exist in the length of time during which either 

 annual plumage is retained ; so that the one might come 

 to be retained for the whole year, the other being com- 

 pletely lost. Thus the Machetes pugnax retains his ruff 

 in the spring for barely tAvo months. Tlie male widow- 

 bird {Chera progm') acquires in Natal his tine plumage 

 and long tail-feathers in December or January, and loses 

 them in March ; so that they are retained during only 

 about three months. Most species which undergo a 

 double moult keep their ornamental feathers for abmit 

 six months. The male, however, of the Avild Gallus 

 haJikiva 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 tlie do- 

 mesticated descendant of this species, the neck-liackles of 

 the male are immediately replaced by new ones ; so that 

 we here see, with respect to part of the j^lumage, a double 

 moult changed under domestication into a single moult." 



" For the forcgoinf^ stiitcracnts in regard to partial moults, and on 

 old males retaining their nuptial plumage, sec Jerdon, on bustards and 



