176 SEA-BIRDS 



The advantages are obvious: the shorter the period of exposure 

 of the eggs and chicks to possible predators the better the chance of 

 survival. On the question of predation, however, we should note 

 that the individual in the large flock is not necessarily able to defend 

 itself better than the individual in the small flock, except that quanti- 

 tatively the individual is safer in the crowd. Although sea-birds are 

 sociable they are ^essentially selfish and non-co-operative outside the 

 family circle; tales of flocks of sea-birds attacking an enemy in forma- 

 tion must be discredited. At most single or a pair of skuas, terns or 

 gulls will mob an intruder, and only provided it is trespassing near 

 their nests; skuas will also employ the broken- wing trick (injury- 

 feigning) to lure an enemy away. These two responses, as distraction 

 displays, are only advantageous in species which are comparatively 

 nimble on land and in the air, and which can easily escape from an 

 enemy; they are entirely instinctive actions, but often have a successful 

 result, especially in drawing mammals from the vicinity of the nest. 

 But gannets, petrels and auks — birds clumsy on land — have no 

 distraction display; when threatened by a predator they remain, at 

 the best, prepared to do battle, or they take flight. Combined operations 

 by sea-birds against a common enemy are quite unknown — otherwise 

 man would not be able to show himself in a large sea-bird colony 

 with no greater hurt than an occasional tap on the head, or a shirt 

 soiled with droppings! However, large colonies of sea-birds are rarely 

 established, and certainly cannot be maintained, except on isolated 

 islands and in other situations where there is minimum interference 

 from terrestrial enemies. 



To recapitulate, the advantage of the large breeding flock lies 

 principally in social stimulation leading to synchronised breeding and 

 so to an earlier and shorter and therefore more successful nesting 

 season. This stimulation may have its source in the greater numbers 

 of experienced breeders in the large flock. There is also the quantitative 

 effect that the individual is safer from normal predation in a crowd; 

 and there is greater alertness against attack because there are more 

 individuals on the watch for enemies. 



Some of these advantages apply in the winter flock, which is 

 principally engaged in the maintenance activities of feeding and safe- 

 roosting; there are the protection and vigilance of numbers, and, 

 besides, the advantage of many pairs of eyes discovering new sources 

 of food supply. If food happens to be scarce the flock spreads far 

 and wide in its search, but does not disintegrate completely. 



