x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 277 
much less brilliant than the male and often quite dull 
coloured. 
Cause of Dull Colours of Female Birds. 
The reason of this phenomenon is not difficult to find, if 
avc consider the essential conditions of a bird’s existence, and 
the most important function it has to fulfil. In order 
that the species may be continued, young birds must be pro¬ 
duced, and the female birds have to sit assiduously on their 
eggs. While doing this they are exposed to observation and 
attack by the numerous devourers of eggs and birds, and it is 
of vital importance that they should be protectively coloured 
in all those parts of the body which are exposed during in¬ 
cubation. To secure this end all the bright colours and 
showy ornaments which decorate the male have not been 
acquired by the female, who often remains clothed in the 
sober hues which were probably once common to the whole 
order to which she belongs. The different amounts of colour 
acquired by the females have no doubt depended on 
peculiarities of habits and of environment, and on the 
powers of defence or of concealment possessed by the species. 
Mr. Darwin has taught us that natural selection cannot 
produce absolute, but only relative perfection; and as a 
protective colour is only one out of many means by which 
the female birds are able to provide for the safety of their 
young, those which are best endowed in other respects will 
have been allowed to acquire more colour than those with 
whom the struggle for existence is more severe. 
Relation of Sex Colour to Nesting Habits. 
This principle is strikingly illustrated by the existence of 
considerable numbers of birds in which both sexes are 
similarly and brilliantly coloured,—in some cases as brilliantly 
as the males of many of the groups above referred to. Such 
are the extensive families of the kingfishers, the woodpeckers, 
the toucans, the parrots, the turacos, the hangnests, the 
starlings, and many other smaller groups, all the species of 
which are conspicuously or brilliantly coloured, while in all 
of them the females are either coloured exactly like the males, 
or, when differently coloured, are equally conspicuous. When 
