170 SEA-BIRDS 



Threat display in fact is now a very important part of the behaviour 

 of the newly independent bird if it is to secure an advantageous 

 position in the winter flock. In the congregations of gulls which feed 

 in farm fields, at rubbish-tips, by sewers, rivers and harbours, and 

 which roost on reservoirs and islands, there is, as in domestic hens, 

 a definite order of precedence, or peck-right, and the flock is so 

 organised that the most dominant bird takes up the best feeding or 

 roosting position, and maintains it by threat actions. In this hierarchy 

 the inexperienced juvenile usually has a low initial status, as in com- 

 munities of men. It will move towards the centre as it grows stronger 

 and more experienced. Some flocks are however composed entirely of 

 juveniles, as those of some gannets, shearwaters, petrels, and puffins 

 which, deserted by their parents before leaving the breeding ground, 

 perform long migrations, and gather at wintering grounds beyond the 

 range of the adults. Little is known of the construction of pelagic 

 flocks ; probably a form of precedence is built up in the same way, 

 both specifically and inter-specifically, in the wide-ranging tube- 

 noses, skuas, terns, and gannets, pelicans, and auks when they become 

 concentrated at rich fishing grounds. We have watched great shear- 

 waters displaying at fulmars in disputing fish-offal at the side of a 

 trawler at Rockall, and fulmar dominated fulmar in the same scramble 

 for food, using the ^characteristic threat display of lowered head, 

 opened wings and cackling noises. 



When the young sea-bird, stimulated by the seasonal development 

 of its breeding organs, returns to the nesting ground for the first time, 

 it has now to overcome two obstacles: the barrier of "individual 

 distance" by which it maintained its position in the flock, and the 

 difficulty of procuring a mate of the opposite sex — if it is to breed 

 successfully. These obstacles are so formidable that the inexperienced 

 bird may never overcome them in the summer of its first return to the 

 land. Its behaviour may remain appetitive, never reaching the stage 

 of consummation: it arrives, establishes or enters a territory, displays 

 and flirts with a bird of the opposite sex, but never copulates (or it 

 copulates too late to breed successfully). However this behaviour is 

 not without its function: from this experience it will be better equipped 

 to initiate successful breeding in succeeding years. 



The male (terns and gulls) is usually the first to arrive at the 

 breeding ground, or at least to occupy a prospective nest-site or 

 pre-territory. He calls loudly as if seeking to attract a partner. But at 

 first he behaves aggressively towards any bird, male or female, which 



