X COLOURS AXD ORXAMEXTS CHARACTERISTIC OF SEX 279 



in holes, usually in banks, but sometimes in trees. The 

 motmots and the puff-birds (Bucconidie) build in similar 

 places ; while the toucans, barbets, trogons, Tvoodpeckers, and 

 parrots all make their nests in hollow trees. This habit, 

 pervading all the members of extensive families, must there- 

 fore be extremely ancient, more especially as it evidently 

 depends in some degree on the structure of the birds, the 

 bills, and especially the feet, of all these groups being unfitted 

 for the construction of Avoven arboreal nests. ^ But in all 

 these families the colour varies gi-eatly from species to species, 

 being constant only in the one character of the similarity of 

 the sexes, or, at all events, in their being equally conspicuous 

 even though differently coloured. 



When I first put forward this view of the connection 

 between the mode of nesting and the coloration of female 

 birds, 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 the females were far less brilliant than the males, 

 although the nest was covered. This is the case with the 

 Maluridae, or superb warblers of Australia, in which the males 

 are very brilliant during the 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 colom^s ; 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 stated the law, I do not think there are 

 any exceptions to it, while there are an overwhelming number 

 of cases which give it a strong support. It has been objected 

 that the domed nests of many birds are as conspicuous as the 

 birds themselves would be, and would, therefore, be of no use 

 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 

 ^ Ou this point see the author's Contributions to Natural Miction, chap. v. L 



