A Theory of Birds' Nests 85 



Considering the very imi)erfect knowledge we possess of the habits 

 of most extra-European birds, the exceptions to the prevalent rule 

 are few, and generally occur in isolated species or in small groujjs. 

 The only marked exceptions I have been able to discover are the 

 following : — 



I. King crows (Dicrourus). These birds are of a glossy black 



colour with long forked tails. The sexes present no differ- 

 ence, and they build open nests. This apparent exception 

 may probably be accounted for by the fact that these birds 

 do not need the protection of a less conspicuous colour. 

 They are very pugnacious, and often attack and drive away 

 crows, hawks, and kites ; and as they are semi-gregarious in 

 their habits, the females are not likely to be attacked while 

 incubating. 



II. Orioles (Oriolidai). The true orioles are very gay birds ; 



the sexes are in many Eastern species either nearly or quite 

 alike, and the nests are open. This is one of the most 

 serious exceptions, but it is one that to some extent proves 

 the rule ; for in this case it has been noticed that the parent 

 birds display excessive care and solicitude in concealing 

 the nest among thick foliage, and in protecting their off- 

 spring by incessant and anxious watching. This indicates 

 that the want of protection consequent on the bright colour 

 of the female makes itself felt, and is obviated by an in- 

 creased development of the mental faculties. 



III. Ground thrushes (Pittidae). These elegant and brilliantly- 

 coloured birds are generally alike in both sexes, and build 

 an open nest. It is curious, however, that this is only an 

 apparent exception, for almost all the bright colours are on 

 the under surface, the back being usually olive green or 

 brown, and the head black, with brown or whitish stripes, 

 all which colours would harmonise with the foliage, sticks, 

 and roots about the nest, and thus serve as a protection to 

 the female bird. 



modifying colour as I am disposed to do. In the same paragraph (p. 240) he 

 alludes to the fact of female liirds and butterflies being sometimes very plain, 

 sometimes as gay as the males, Ijut apparently considers this mainly due to 

 peculiar laws of inheritance, which sometimes continue acquired colour in the 

 line of one sex only, sometimes in both. Without denying the action of such 

 a law (which Mr. Darwin informs me he has facts to support), I impute the 

 difference, in the great majority of cases, to the greater or less need of protection 

 in the female sex in these groups of animals. 



