x COLOURS AXD 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 

 we consider the essential conditions of a bud'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 



