Chap. VIII.] SEXUAL SELECTION. 261 



and many of the species are, as is well known, polyga- 

 mous ; others being strictly monogamous. What a con- 

 trast is presented between the sexes by the polygamous 

 peacock or pheasant, and the monogamous guinea-fowl 

 or partridge ! Many similar cases could be given, as in 

 the grouse-tribe, in which the males of the polygamous 

 capercailzie and black-cock differ greatly from the fe- 

 males ; while the sexes of the monogamous red grouse 

 and ptarmigan differ very little. Among the Cursores, no 

 great number of species offer strongly-marked sexual 

 differences, except the bustards, and the great bustard 

 ( Otis tarda) is said to be i^olygajtnous. With the Gralla- 

 tores, extremely few species differ sexually, but the ruff 

 {Machetes pugnax) affords a strong exception, and this 

 species is believed by Montagu to be a polygamist. Hence 

 it appears that with birds there often exists a close rela- 

 tion between polygamy and the develoj)ment of strongly- 

 marked sexual differences. On asking Mr. Bartlett, at 

 the Zoological Gardens, who has had such large experi- 

 ence with birds, whether the male tragopan (one of the 

 Gallinaceae) was polygamous, I was struck by his answer- 

 ing, " I do not know, but should think so from his S])lcn- 

 did colors." 



It deserves notice that the instinct of pau-ing with 

 a single female is easily lost under domestication. The 

 wild-duck is strictly monogamous, the domestic duck 

 highly polygamous. The Rev. W. D. Fox informs me 

 that with some half-tamed wild-ducks, kept on a large 

 pond in his neighborhood, so many mallards were shot by 

 the gamekeeper that only one was left for every seven or 

 eight females ; yet unusually large broods were reared. 

 The guinea-fowl is strictly monogamous ; but Mr. Fox 

 finds that his birds succeed best when he keeps one cock 

 to two or three hens." Canary-birds pair in a state of na- 



' The Rev. E. S. Dixoa, however, speaks positively (' Ornamental 



