142 THE COURTSHIP OF ANIMALS 



russet and black with that of the Sun Bittern {Eurypyga 

 helias) in like mood, whose wings and tail when spread, 

 and only then, display bands of vivid chestnut-red, 

 contrasting with bands of black, on a background of grey 

 and buff, variegated with delicate mottlings and vermi- 

 culations of black and brown, and streaks of white. 

 In the case of the Warblers, it is to be remarked, the male, 

 in these ecstatic moods, will commonly hold a leaf, or a 

 piece of stick, in his beak, as if suggesting the work of nest- 

 building and its delightful sequence. This, or its equiva- 

 lent, is a common phase, for the Great Crested Grebe, for 

 example, in these paroxysms will dive and bring up weed, 

 the nest material of the species, as an offering to his 

 mate, or as a stimulant to her yet slumbering passion. 



It seems clear, then, that the evolution of colour is not 

 the stimulant to display, for this is present where con- 

 spicuous colours are wanting. Yet it can readily be 

 understood how the association of ideas in regard to 

 colour and display arose, for there are cases where this 

 interpretation seems inevitable. Such are afforded by 

 certain sea-birds like the Kittiwake, Guillemot, Fulmar 

 and Cormorant, wherein the inside of the mouth is of a 

 lurid orange-red in the case of the first-mentioned, and 

 of flaming gamboge yellow in that of the others. During 

 moments of sexual ecstasy the mouth is widely opened, 

 as if to charm the beholder with its gaudy hue. Both 

 sexes have the same colouring, and both behave alike. 

 But it is doubtful whether either is conscious that its 

 own mouth is like that exposed to its gaze : the action 

 is sympathetic. No doubt it may play its part in stimu- 

 lating desire, but we cannot contend from this that it 

 has been evolved by sexual selection, that is to say, that 

 the hues have undergone a process of gradual intensi- 



