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Show 214 SEXUAL SELEC'fiON : BIRDS. cause. Some birds moult so early, that nearly. all the body-feathers are cast off before tho fi~st wm~feathers are fully grown; and we cannot believe t~,tt this was the primordial state of things. When the per~ocl of mou ltm. g has been accelerated ' the aOo 'e at whiCh the colours of the adult plumage were first d~veloped would falsely appear to us to have been carher t~an it really was. This may be illustrated by the practiCe followed by some bird-fanciers, who pull out a few feathers from the breast of nestling bullfinches, a~d from the head or neck of young gold-pheasants, m order to ascertain their sex ; for in the males these feathers are immediately replaced by coloured ones.36 The actual duration of life is known in but few birds, so that we can hardly judge by this standard. And with reference to the period at which the powers of re~roduction are gained, it is a remark~b!e fact ~h~t variOus birds occasionally breed whilst retannng thmr Immature pl umo,ge. 37 • • • • 'l'he fact of birds breedmg m their Immature plumage seems opposed to the belief that sexual selection has 3G Mr. lllyth, in Charleswort!J's 'Mag. of Nat. IIi ~t.' vol. i. 1837, p. 300. Mr. Bartlett bas informed me in regard to gold-pb easan~s. . 37 I have noticed tho following cases in Audubon's 'Ormth. :nwgraphy. The Redstart of America ' (Muscicapa 1'u.ticilla, v~l. 1. Jl. 203). 'l.'he Ibis tmdalus takes four years.~.o com ~ to f~~l matunty, bu.t sometime':! breeds in the second year (vol. 111. p. 133;. Iho Crus Amerlcantts takes the same time, but breeds before acquiring its full plumage (vol. iii. p. 211). Tho adults of Ardea cwrulect 11rc blue and tho young white ; and white, mottled, nnd mature Llue birds may all bo seen breouing together (vol. iv. p. 58) : but Mr. Blyth informs m? t~11~t certain herons apparently arc dimorphic, for white and colom cd tnthVldu~ls of the same ago may be observed. The Harlequin duck (Anas htstrionica Linn.) takes three years to acquire its full plumage, tho~gh many birds breed in the ~ocond year (vol. iii. p. GH). The Wlutcheadcd Eagle (Falco leucocephctlus, vol. iii. p. ~10 ) is .likewise known to breed in it::~ immature state. orne spec10s of Onolus (accordiug to Mr. Blyth and 1\Ir. Rwinhoc, in ' Ibi~,' July, 1 8G3, p. G8} likewise breed before they atta in tlt cir fullplumngc. CHAP. XVI. THE YOUNG LIKE BOTII ADULTS. 215 played as important a part, as I believe it has, in giving ornamental colours, plumes, &c., to the males, and, by means of equal transmission, to the females of many species. The objection would be a valid one, if the younger and less ornamented males were as successful in winning females and propagating their kind, as the older and more beautiful males. But we have no reason to suppose that this is the case. Audubon speaks of the breeding of the immature males of Ibis tantalus as a rare event, as does Mr. Swinhoe, in regard to the immature males of Oriolus.38 If the youn()' of any species in their immature plumage were mor~ successful in winning partners than the adults, the adult plumage would probably soon be lost, as the males which retained their immature dress for the longest period would prevail, and thus the character of the species would ultimately be modified.39 If, on the other hand, the young never succeeded in obtaining a female, the habit of early reproduction would perhaps be sooner or later quite eliminated, from being superfluous and entailing waste of power. ~rhe plumage of certain birds goes on increasing in ~8 Sec tho last foot-note. 3 ~. Other animals, belonging to quito distinct classes, are either lw.ln~ually or. occasionally capable of b1·eeding before they have fully 11..:qULrcd theu adult characters. This is tho case with tho young males of the salmon. Several amphibians have been known to breed whilst retaining their larval structure. Fritz Miiller bas shown ('Facts and Argumcn.ts for Darwin,' Eng. trans. 18GD, p. 79) that the males of several. amplnpod Cl:us~aceans become sexually mature whilst young; and I 111fcr that tlu.s lS a case of premature breeding, bccauso they have ~ot us.yet acqu1red theit· fully-developed claspers. All such facts arc btghly Interesting, as bearing on one means by which sp cics may u?dergo great modifications of character, in accordance with Mr. Cope's VI.cws, c~pressed under tho terms of tho " retardation and acceleration of gencn c characters ; " but I cannot follow tl1c views of this eminent naturalist to th eir full extent. Sec 1\ir. Cope "On tho Origin of Genera" fwm tho 'Pmc. of Acad. Nat. Sc. of Philadel1)hia,' Oct. 1868. ' |