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Show 174 SEXUAL SELECTION : BIRDS. PAitl' 11. <:olourino- often characterises allied forms, that in three species of Dacelo the malo differs fro~ the female o~ly in tho tail being dull-blue banded with black, wh1lst that of the female is brown with blackish bars; so that hero tho tail differs in colour in the two sexes in exactly tho same manner as the whole upper surface in the sexes of Carcinoutes. w·ith parrots, which likewise build in holes, we find aualoO'ous cases: in most of the species both sexes are brilli:ntly coloured and undistinguishable, but in .n?t a few species the males are coloured rather more VIVIdly than the females, or even very differently from them. (rhus besides other strongly-marked differences, the whol~ under surface of the male King Lory (Aprosmictus scapulatus) is scarlet, whilst the throat and chest of the female is green tinged with reel : in the Euphema splendida there is a similar difference, the face and wingcoverts moreover of the female being of a paler blue than in the male.22 In the family of the tits (Parinm), which build concealed nests, the female of our common blue tomtit (Pw·us cmrule~ts) is "much less brightly coloured" than the male; and in the magnificent Sultan yellow tit of India the difference is greater.23 Again in the great group of the woodpeckers/4 the sexes are generally nearly alike, but in the Megapious validus all those parts of the head, neck, and breast, which are crimson in tho male are pale brown in the female. As in several woodpeckers the head of tho male is bright crimson, whilst that of tho female is 22 Every gmdation of diflcrenco beL ween the sexes may be followed in the panots of Australia. See Gould's 'Handbook,' &c., vol. ii. p.H-102. 2:1 Macgillivrn.y's 'British Birds,' vol. ii. p. 433. Jordon, 'Birds of Iudin.,' vol. ii. p. 282. ~·I All tho following facts are taken from M:. Malhcrbe's magnificent ' Monographic des Picidces,' 1861. .CHAP. XV. COLOUR AND NIDIFICATION, 175 plain, it occurred to me that this colour might possibly make the female dangerously conspicuous, whenever she put her head out of the hole containing her nest, and consequently that this colour, in accordance with Mr. Wallace's belief, bad been eliminated. This view is strengthened by what Malherbe states with respect to Indopicus carlotta; namely, that the young females, like the young males, have some crimson about their heads, but that this colour disappears in the adult female, whilst it is intensified in the adult male. Nevertheless the following considerations render this view extremely doubtful: the male takes a fair share in incubation,25 and would be thus far almost equally exposed to danger; both sexes of many species have their beads of an equally bright crimson; in other species the difference between the sexes in the amount ' of scarlet is so slight that it can hardly make any appreciable difference in the danger incurred; and lastly, the colouring of the bead in the two sexes often differs slightly in other ways. The cases, as yet given, of slight and graduated differences in colour between the males and females in the groups, in which as a general rule the sexes resemble each other, all relate to species which build d?me~ or concealed nests. But similar gradations may hkewise be observed in groups in which the sexes as a general rule resemble each other, but which build <>pen nests. As I have before instanced the Australian parrots, so I may here instance, without giving any details, the Australian pigeons.26 It deserves especial notice that in all these cases the slight differences in 26 Audubon's ' Ornithological Biography,' vol. ii. p. 75; see also the ' Ibis,' vol. i. p. 268. ~0 Gould's' Handbook of the Birds of Australia,' vol. ii. p. 109-14!), |