RIVER TERNS 113 



between which and the river bank there is a sufficient 

 depth of water to prevent jackals fording it. If the 

 island contain eggs or young ones, the parent birds 

 will make a hostile demonstration by collecting over- 

 head and flying backwards and forwards, uttering 

 their harsh cries, and the nearer one approaches the 

 nest the more clamorous do they become. In this 

 manner they unwittingly inform the nest-seeker 

 whether he is getting " hot " or " cold," to use the 

 expressions employed in a nursery game. 



The terns which breed on islets in Indian rivers 

 do not appear to do much incubating in the daytime. 

 There is no need for them to do so, because the sand 

 grows very warm under the rays of the sun. Moreover, 

 the only foes to be feared are the crows and the kites, 

 which the terns can keep at bay more effectually when 

 on the wing than while sitting on the eggs. Very different 

 is the behaviour of the sea terns, whose eggs are liable 

 to attack by gulls and crabs. For safety's sake the sea 

 terns lay in large colonies, and, to use Colonel Butler's 

 expression, sit on their eggs ** packed together as close 

 as possible without, perhaps, actually touching one 

 another." He once came upon the nests of a colony 

 of large-crested terns {Sterna hergii). The sitting birds 

 did not leave their eggs until he was within a few yards 

 of them. Having put them up, he retired to a little 

 distance. " No sooner had I done so," he writes, " than 

 both species [i.e. the gulls and terns] began to descend 

 in dozens to the spot where the eggs were lying. In a 

 moment a general fight commenced, and it was at once 

 evident that the eggs belonged to Sterna hergii, and that 



