x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 279 
in holes, usually in banks, but sometimes in trees. The 
motmots and the puff-birds (Bucconidse) build in similar 
places; while the toucans, barbets, trogons, woodpeckers, 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 woven arboreal nests . 1 But in all 
these families the colour varies greatly 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 
Maluridse, 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 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 stated the law, I do not think there are 
any exceptions to it, Avhile 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 
1 On this point see the author’s Contributions to Natural Selection , chap. v. i. 
