152 



SEXUAL DIMORPHISM 



who remain long in the nest. The superior size and strength 

 here, in fact, are, I think, related to hunting rather than to 

 fighting. 



Otididw. In the Bustard family, Otididae, sexual differ- 

 ences of some importance occur. In the Great Bustard, Otis 

 tarda, the male is considerably larger than the female ; he has 

 curious whisker-like plumes on the cheeks, which are absent 

 in the female, and has a great air-pouch opening from beneath 

 the tongue, which is also absent in the female. The female 

 differs slightly in colour. Considering the very marked and 

 elaborate " display " or erection of the feathers which is per- 

 formed by the male in courtship, it might be suggested, that if 

 the views I am maintaining are correct, the peculiarities of the 

 male ought to be more developed than they are. But the erectile 

 feathers are probably larger in the male than in the female, 

 though they are of the same colour, namely, most of them 

 white. In the attitude of display the throat pOuch is inflated 

 so as to distend the neck and throat to a prodigious extent. 

 The tail is turned forwards flat on the back, and the white 

 under tail-coverts are erected to form a frill behind. White 

 secondary wing feathers are erected on each side of the back, 

 and the head is buried in the feathers of the neck, so that the 

 whiskers are caused to stand erect on each side. 1 In these 

 movements we have stimulation applied to the special 

 feathers on the cheeks corresponding to their special develop- 

 ment, and also a mechanical explanation of the throat-pouch. 

 In other species, there is, in the male, a special shield of 

 feathers over the crop, composed of the elongated feathers of 

 the throat and neck, an erectile crest on the crown of the 

 head, and a large ruff of soft plumes on the sides of the neck 

 (genus Houhara). These adornments are much less developed 

 in the female, and doubtless all correspond to special move- 

 ments in the sexual gestures. 



1 R. Bowdler Sharpe, Birds of Great Britain, vol. iii., 1896. 



