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Show 218 SEXUAL SELECTION: BIRDS. PAilT u. waders. Lastly, in regard to the young differing greatly from both sexes in their adult summer aml winter plumages, this occurs with some herons and co-rets of North America and India,-the young alone b being white. . I will make only a few remarks on these compl.ICated cases. ·when the young resemble the !emal~ m_ her summer dress, or the adults of both sexes m their wmter dress the cases differ from those given under Ol~sses I. and III. only in the characters originally ac~mred by the males during the breeding-season, ha:mg been lmited in their transmission to the correspondmg se~son. When the adults have a distinct summer and wmt~1· plumage, and the young differ from both, th.e case 1s more difficult to understand. V\7 e may adm1t as probable that the young have retained an ancient st~te of plumage ; we can account through sexual selectw:n for the summer or nuptial plumage of the adults, but how are we to account for their distinct winter plumage? If we could admit that this plumage serves in all cases as a protection, its acquirement would be a s.imple affair · Lut there seems no good reason for th1s admissi; n. It may be suggested that the widely different conditions of life during the winter and summer have acted in a direct manner on the plumage ; this may have had some effect, but I have not much confidence in so great a difference, as we sometimes see, between the two plumages having been thus caused. A more probable explanation is, that an ancient style of plumage, partially modified through the transference of s?me characters from the summer plumage, has been retamcd by the adults during the winter. Finally, all the cases in our present class apparently de~end on char~cters acquired by the adult males, havmg been vanously limited in their transmission according to age, season, Cu. X\'I. '!'liE YOUNG LIKE ADULTS OF SAME f:!EX. 219 and sex; but it would not be worth while to attempt to follow out these complex relations. CLASS VI. The young in their first plumage differ from e~ch other according to sex ; the yo·ung males resembhng nwre or less closely the adult males, and the r~ung fema~es more or less closely the adult females.lh~ cases m the present class, though occurring in varwus groups, are not numerous ; yet, if experience had not t~ught us to the contrary, it seems the most natural thmg that the young should at first always resemble to a c~rtain extent, and gradually become more and more like, the adults of the same sex. The adult male blackcap (Sylvia atricapilla) has a black hea~, that of the female being reddish-brown; and I am mfor:n~d b~ Mr. Blyth, that the young of both sexeR can be d1st~ngmshecl by this character even as nestlings~ In the family of thrushes an unusual number of similar cases have been. noticed; the male blackbird (Turdus merula) ca~ be ~1stinguished in the nest from the female, as the mam wmg-feathers, which are not moulted so soon as the body-feathers, retain a brownish tint until tho ~econ~ general moult.46 The two sexes of the mockI~ g bn·cl (Turdus polyglottus, Linn.) differ very little no.m each other, yet the males can easily be distin~ mshed at a very early ago from the females by shewmg more pure whiteY 'rhe males of a forest-thrush and of. a rock-thrush (viz. Orocetes erythrogastra and Petroc~ncla cyanea) have much of their plumage of fine blue, whilst the .females are brown; and the nestlin; males of both s~ecws have their main wing and tailfeathers edged w1th blue, whilst those of the female are 41i Blytl~, in Chnrlosworth's '1\fog. of Nat. IIi t' vol i 1837 p 3G'> . and from mformation given to me by him. . . . ' . - ' 47 Audubon, ' Ornith. Biography,' vol. i. p. 113. |
