OCR Text |
Show SEXUAL SELECTION: BIRDS. PART If. manner, from the adult female. Innumerable instances in all Orders could be given; it will suffice to call to mind the common pheasant, duck, and house-sparrow. The cases nuder this class graduate into others. r.rhusthe two sexes when adult may differ so slightly, and the Youno- so slio-htlv from the adults, that it is doubtful b b • whether such cases ought to come under the present, or under the third or fourth classes. So again the young of both sexes, instead of being quito alike, may differ j n a slight degree from each other, as in onr sixth class. r.rhese transitional cases, however, are few in number, or at least are not strongly pronounced, in comparison with those which come strictly under the present class. The force of the present law is well shewn in those O'roups in which as a general rule, the two sexes and ~1e yo~ng are all alike; for when the male in these groups does differ from the female, as with certain parl'Ots, kingfishers, pigeons, &c., the young of both sexes resemble the adult female.2 vVe see tho same fact exhibited still more clearly in certain anomalous cases; thus the male of Heliothrix auriculata (one of the humming- birds) differs conspicuously from the female in having a splendid gorget and fine ear-tufts, but the female is remarkable from having a much longer tail than that of the male ; now the young of both sexes 2 Sec, for instance, 1\'lr. Gould's account (' Htwdbook of the Birds or .\.ustralia,' vol. i. p. VJ3) of Cynnalcyon (one of tbc Kingfishers) in which, liowcvor, the young male, though resembling the adult fcnmlc, is l ss brilliantly coloured. In some species of Dacclo the mules lmvc blue tails, and the females brown ones ; and 1\'[r. R B. Sharpe informs mo tlint tho tail of the young male of D. Gaudichctttcli i~ nt first brown. Mr. Gould hns d::!scribcd (ibid. vol. ii. p. 14, 20, 37) the sexes and tho young of certain lllack Cockntoos and of the King Lory, with which tho same rule vrcvail~. Also Jordon(' Bir(ls of Iudiu,' vol. i. p. :lGO) on tho Palmomid 1·osa, in which tho young arc more like the fcmnlo tlmn the male. Soc Audubon (' Oroith. Biogro.ph.' vol. ii. p. 175) on the two sexes and tho young of Columba passm·ina. C HAP. XVI. TilE YOUNG LIKE THE ADULT FEMALES. 189 T~semble (with the exception of the breast being spotted With bronze) the adult female in all respects jncludiug the length of heL" tail, so that the tail of the male ~etually becomes sh.orter as he reaches maturity, which lS a most unusual Circumstance.3 Again, the plumage ·of.the male goosandet· (Mergus merganser) is more conS~ ICuously coloured, with the scapular and secondary wmg-feathers mueh longer than in the female, but differ~ e~tly from what occurs, as far as 1 know, in any other Ln·d, the crest of the adult male, though broader than t~at of the female, is considerably shorter, being only a ht~le above an inch in length; the crest of the female be1ng two and a half. inches long. Now the young of both sexes resemble m all respects the adult female .so that their crests are actually of greater length thou()'!; narrower than in the adult male.4 ° When the young and the females closely resemble e~ch other and both differ from the male, the most obVIOus conclusion is that the male alone has been modined. Even in the anomalous cases of the Heliothrix and Mergus, it. is probable that originally both adult .sexes we~·e furmshed, the one species with a much elongated tail, and the other with a much elonO'ated crest these characters having since been partially lost by th~ .ad.ult ~ales from some unexplained cause, and trans~ mitted m their diminished state to their male offsprinO' alo~1e, when arrived at the corresponding age of rna~ tunty. ~rhe belief that in the present class the male alone has been modified, as far as the differences between the male and the female together with her young are concerned, is strongly supported by some 3 1 1 owhc. this infor~ation to Mr. Gould who shewed me the specimens· se~ a ~o ~s : Intr~uc~ion to the 'l'rochilidro,' 1861, p. 120. ' _ Macgtlhvmy, lllst. Brit. Birds,' vol, y, p. 207-214. |