THE GULLS 245 



incubated them, and in some instances did not lay any eggs of their 

 own. A skua will not recognise its own egg if this is placed outside the 

 nest, but will devour it. 



Gulls are born with their eyes open, and are covered with a thick 

 down. They are able to walk almost immediately. When danger 

 threatens the Larus chick will leave the nest when it is only two days old 

 and, at the alarm cry of the adults, will try to hide in some nearby 

 crevice, or crouch under a tuft of herbage. At the age of five to six 

 days and upwards it runs freely, and often in its haste to escape an 

 enemy it will walk right over the edge of a cliff. This is a frequent 

 cause of mortality when human beings walk about in gulleries. If 

 the chicks drop from a great height they may be killed, but falling 

 from lesser heights they may bounce unhurt from the rocks and boulders 

 below ; if these are sufficiently shelving and tiered, they may be able 

 gradually to climb back to the nesting site, by hooking themselves 

 along with beak, legs and their unfeathered wings, encouraged by the 

 calls of their parents — always provided they are not intercepted by 

 some predator. In normal undisturbed conditions, however, the young 

 Larus gull remains on or near the nest for a month to six weeks. 



The diet of the large Larus adults changes to one of small crabs, 

 shrimps and fish when the young are first hatched. These are fed by 

 both parents; at first the female has begged the male for food with 

 which she has fed both herself and the chicks. The male brings in a 

 crop loaded with food, and on the begging of his mate he regurgitates 

 this in front of her. Frequently both adults and chicks will then pro- 

 ceed to devour the salivated mass, the adults picking up and holding 

 the food in the bill so that the chicks can feed more easily. As the chicks 

 grow larger and stronger they themselves beg for food insistently, 

 stretching up to tap the bill or peck the face of the parent newly 

 arrived with a full crop. They show a definite reaction to bright objects 

 by pecking. N. Tinbergen has proved that the red spot on the bill 

 of the adult is a signal (releaser) to the young that food is ready. The 

 occurrence of red on the bills of gulls and terns thus has a special 

 significance; but other fish-eating species such as cormorants and 

 gannets have no brightly coloured bill spot, although the young bird 

 invites feeding by a similar tapping or pecking action. Young kitti- 

 wakes, like young gannets, grope into the parental gullet for the regurg- 

 itated fish. 



The manners of the young Larus gulls become more and more 

 unruly, and they soon learn to snatch at the food before it has been 



