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Show 278 DARWINISM CHAP. searching for some cause for this singular apparent exception to( the rule of female protective colouring, I came upon _a fact which beautifully explains it; for. in all t?ese cas~s, with~':t exception, the species either nests m holes m the ground or Ill trees or b m" ld s a domed or covered n· est' so as completely to conc~al the sitting- bird. We have bore a cas~ exactly parallel to that of the butterflies prote?ted by distastcfn! ness whose females are either exactly bke the males, o~·, 1f diff~rent arc equally conspicuous. We can hardly belwvc that so 'exact a parallel should exist . between such remote classes of animals, except under the mfluence of a g~neral 1 . d 1"n the need of protection by all defenceless ammali=l, aw, an , · d h l and especially by most female insects and b1r s, we ave snc 1 1 Whl.ch has been !)roved to have influenced the colours a aw, . . k" d 1 of a considerable proportiOn of the ammal mg om. The general relation which exists bct:vcen the mode of nesting and the coloration. of the sexes 1? those groups of birds which need protectwn from enemies, may be thus expressed : When both sexes are . b:illia~t or conspicuous, the nest is such as to conceal the s1ttmg-b1rd; but when the · male is brightly coloured and the female sits exposed_ on the nest, she is always less brilliant and generally of qmte sober and protective hues. It must be understood that the mode of nesting has in-fluenced the colour, not that the colour has determined the mode of nesting; and this, I believe, has been generally, thongh not perhaps universally, the case. For we ~mow th~t colour varies more rapidly, and can be more easily modified ~n<l fixed by selection, than any other character; whereas hal)Jts, especially when connected with structure, _and when th<'y pervade a whole group, are much more. persistent and m~n ·n difficult to cbano-e as shown by the hab1t of the dog tun ting • b' . . round two or three times before lymg down, believed to be that of the wild ancestral form which thus smoothed down the herbage so as to form a comfortable bed. W c sec, too, that the general mode of nesting is characteristic of whole families differing widely in size, form, and colours. Thus, all the kingfishers and their allies in every part of tho world nest 1 See the author's Contributions to Natural &lection, chap. vii. , in which these facts were first brought forward, x COLOURS AND ORNAMENTS CITARACTERISTIC OF SEX 279 in boles, usually in banks, but sometimes in trees. The motmots · and the puff-birds (Bucconidre) build in similar places; while the toucans, barbcts, trogons, woodpeckers, and parrots all make their nests in hollow trees. This habit, pervading all the mom bers of -extensive families, must therefore be extremely ancient, more especially as it evidently depends in some degree on the structure of the birds, the oills, and especially the feet, of all these groups being unfittc<.l for the construction of woven arboreal nests.1 But in all these families tho colour varies greatly from species to species, being constant only in tho one character of the similarity of the sexes, or, at all events, in their being equally conspicuous oven though differently coloured. When I first put forward this view of the connection between tho mode of nesting and the coloration of female hirds, I expressed the law in somewhat different terms, which gave rise to some misunderstanding, and led to numerous criticisms and objections. Several cases were brought forward in which tho females were far less brilliant than the males, although the nest was covered. This is the case with the Maluridre, or superb warblers of Australia, in which tho males are very brilliant during tho pairing season and the females quite plain, yet they build domed nests. Here, there can be little doubt, the covered nest is a protection from rain or from some special enemies to the eggs ; while the birds themselves are protectively coloured in both sexes, except for a short time during the breeding season when the male acquires brilliant colours; and this is probably connected with the fact of their inhabiting the open plains and thin scrub of Australia, where protective colours are as generally advantageous as they are in our north-temperate zones. As I have now st.'ttod the law, I do not think thoro arc any exceptions to it, while there arc an overwhelming numocr of cases which give it a strong support. It has been objected that the domed nests of many birds arc as conspicuous as the birds themselves would be, and would, therefore, be of no usc as a protection to the birds and young. But, as a matter of fact, they do protect from attack, for hawks or crows do not pluck such nests to pieces, as in doing so they would be 1 On this point see the autlwr'l! Contrib'll!tions (o Natural Selection, chap. v. i. |