88 THE TERNS 



species, the sexes share the work of incubation according to 

 Naumann. The down-clad chicks are hatched at the end of three 

 weeks. They are dimorphic (see " Classified Notes "), the difference, 

 in the case of the Arctic-tern, extending to the coloration of the 

 upper parts and legs, and in the case of the common-tern to beak 

 also. The difference between the two types of chicks of the latter 

 species is said to extend even to their disposition, that with flesh- 

 coloured legs being more lethargic than the one with red legs. 1 A 

 curious fact, which I noted some years ago, is that the chicks of 

 both these species, as well as those of the sandwich-tern and black- 

 headed-gull, have a vestigial claw on the bastard wing. This will 

 probably prove to be the case with all the Laridce, if not the Limicolce 

 as well. Why it should have survived in the case of ground-nesting 

 birds is difficult to explain. The only species in which wing-claws 

 are habitually functional is the hoatzin of S. America, a tree-nesting 

 bird, whose chick uses its claws, when alarmed, to clamber out of 

 its nest away into the adjoining foliage. It loses the claws when 

 fully fledged. 



The coloration of the chicks, when they are on rough stony 

 ground or shingle, is highly protective. The markings on the back 

 and flanks still further aid concealment by serving to break up the 

 outline of the body, so that it does not stand out against its back- 

 ground. The chicks of both species quit the nest almost as soon as 

 they can run. Whether they ever subsequently return to it I am not 

 certain, but think not. They leave it either to meet the parent 

 coming with food or else to seek shelter from the sun, not from fear 

 of human beings. During the first few days, indeed, the tern chick 

 has not learnt fear, as the following incident, among many, will show. 



1 Common-tern : Auk, xiii., 1896, p. 51 (G. H. Mackay, whose observations were verified by 

 R. Ridgway and W. Brewster). See also British Birds, Hi. 169, Oct. 1909 (H. W. Robinson), for 

 the same observations made independently. At Dungeness, in 1908, 1 noted that some chicks 

 were a much darker buff than others. Arctic tern : British Birds, in., 1909, 200 (N. F. Ticehurst). 

 In July 1905 I photographed at Walney, in an Arctic-tern colony, two chicks, one grey in ground- 

 colour, the other buff. All the adult terns I saw in the part of the colony in which these chicks 

 were belonged to the Arctic form. 



