502 BIRD BEHAVIOUR xvn. 7- 



The various forms of billing and gaping ceremony probably 

 represent a further degree of abstraction from ritual feeding. A variety 

 of birds touch bills during courtship, for instance, gulls, ravens, great 

 crested grebes, and some finches. The inside of the mouth is some- 

 times brilliantly coloured in adults, as it is in so many nestlings; it is 

 green in some birds of paradise, yellow in many birds. During display 

 it may be opened suddenly, producing an obvious effect on the mate, 

 who approaches fascinated into a state of passive acceptance by this 

 surprising revelation, perhaps recalling a possibility of satisfaction 

 remembered from childhood. 



Other aspects of the courtship may show this reversion to infantile 

 behaviour. Thus, in female sparrows and many other birds one or 

 both wings are held drooping and fluttering during display, as they 

 are by the chick craving food or by the frightened adult ; a behaviour 

 known as injury feigning or distraction display. The female hedge- 

 sparrow may quiver with one wing and open her bill to the male at the 

 same time. This injury- feigning also has survival value in distracting 

 the attention of a predator from the nest, as can be well seen in plovers 

 and other ground-nesting birds. Some plovers have different displays 

 for use against different types of nest enemy. 



The effects of bird display are by no means restricted to ensuring 

 mutual recognition of males and females and stimulating them to 

 coition, especially important though such functions must be in 'flighty' 

 creatures. The element of threat and even fighting with other males 

 is very common. It is seen in its purest form in such birds as the 

 blackcock and ruff, which are promiscuous. The male ruffs congre- 

 gate on a chosen 'courting ground' and go through an elaborate series 

 of ritual fights. The females ('reeves') do not take part in this pro- 

 cedure, but at intervals one of them will 'select' a male by fondling 

 him with her bill and then adopt the receptive attitude for copulation. 

 Selous, who observed this display, noted that males with large ruffs 

 were chosen especially often. Such selection of males by females was 

 the basis of Darwin's theory of sexual selection, the supposition being 

 that the males chosen would be the most gorgeous, victorious, and 

 hence most vigorous and effective breeders. Selous recorded that in 

 one area, during a period of 3! hours, there were 12 copulations, 10 of 

 them with a single male. It must be very difficult when observing 

 birds to establish exactly the actions and relationships of males and 

 females and hence to distinguish between the 'stimulation' of female 

 by male and 'selection' of male by female. Perhaps there is only a 

 verbal difference between the two. 



