i8o THE BIOLOGY OF BIRDS 



To return to the editorial summary of Professor 

 Whitman's observations. " As the period of consummation 

 approaches, the composition of the activities changes with 

 the addition of new elements. Along with bowing, there is 

 billing and fondUng of each other's head, hugging or necking, 

 jumping over the female without any attempt at mounting, 

 opening the beak by the male, inserting of the female's beak 

 in his, and often the shaking and rattling of the crop as if the 

 male fed the female. The female stoops with lowered head, 

 the male mounts with a jump, the female raises her wings as 

 a support and lifts the tail, while the male reaches back, 

 moving the tail from side to side until contact is 

 effected." 



Some features in the later courtship behaviour are 

 suggestive of, or tend to induce the attitude of sexual union. 

 This may be said of the way in which the erotic male jumps 

 quickly over the back of the female, or of the way in which the 

 birds hug one another by the neck. In many different kinds 

 of pigeons the male receives the female's mouth within his 

 own, and he may regurgitate a little food. This close contact 

 of surfaces may increase the sexual excitement as in amatory 

 kissing, but it is possibly suggestive, since both parents feed 

 their young in a closely similar fashion. " In many organisms 

 there seems to be an intimate functional relation between the 

 sexual activities and those processes involved in the care and 

 feeding of the young " (Whitman, 1919, III. p. 107). 

 Dr. Riddle observed that two old males which incubated 

 eggs and fed the young, prolonged the feeding period till 

 eventually the sexual note was struck on both sides. The 

 young bird was at first primarily interested in the food, but 

 the continuance of the activity finally aroused a sexual 

 response before maturity {ibid. p. 108). 



§ 4. The Courtship of the Great Crested Grebe 



The sexes in grebes are quite like one another, the usual 

 plumage being dusky brown or blackish grey above and 

 silvery white below. The glossy satin- white of the lower 



