Chap. XY. 
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, had 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. Never- 
theless the following considerations render this view 
extremely doubtful: the male takes a fair share in 
incubation,^^ and would be thus far almost equally 
exposed to danger ; both sexes of many species have 
their heads 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 head 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 
domed or concealed nests. But similar gradations may 
likewise be observed in groups in which the sexes 
as a general rule resemble each other, but which build 
open nests. As I have before instanced the Australian 
parrots, so I may here instance, without giving any 
details, the Australian pigeons.^® It deserves especial 
notice that in all these cases the slight differences in 
25 Audubon’s ‘ Ornithological Biography,’ vol. ii. p. 75; see also the 
‘ Ibis,’ vol. i. p. 268. 
25 Gould’s ‘ Handbook of the Birds of Australia,’ vol. ii. p. 109-149. 
