248 SEA-BIRDS 



of its eggs and chicks to predators. Keighley & Lockley (1947), 

 observing ten nests from 4 July to 1 4 August in Pembrokeshire, found 

 that only two chicks eventually flew, the remaining fourteen eggs or 

 chicks having been taken, one by one, by Lams gulls. 



In northern waters where its feeding grounds are close at hand, 

 the kittiwake will occasionally nest on the ledges of buildings over- 

 looking the sea. It frequently builds well inside caves, and, in the 

 Arctic, on precipices some distance inland. A most unusual site is 

 recorded by Salomonsen (1941c) on Tyrholm in the bird sanctuary 

 of Hirsholmene in the Kattegat. In a colony of 2,902 pairs of black- 

 headed gulls, 437 pairs of Sandwich terns, 6 of black guillemot and 

 3 of common gull, were 1 1 pairs of kittiwakes, which had placed their 

 nests on the ground, among boulders or in lyme-grass clumps, an 

 interesting abnormality. It was found that the chicks in these kitti- 

 wake nests made no attempt to run from them on the approach of 

 human intruders, as Lams chicks do. The adults also remained at the 

 nest, showing the typical cliff-nesting fearlessness. There is also a dune 

 record for Britain (p. 238). 



The fledging-periods of most gulls are difficult to assess accurately 

 since Lams chicks may wander from the nest for considerable distances 

 before they become independent of the adults ; and the adults them- 

 selves become less territorially minded at this stage, moving the 

 "defended" area around the growing bird as the young bird itself 

 moves, and gradually losing interest in the chick and its safekeeping. 

 The age at which the young gull is able to fly for the first time may 

 be reasonably considered its fledging period. But of this period sur- 

 prisingly little appears to be known with certainty. The following 

 figures therefore are estimates only: 



Estimated fledging-periods of Gulls and Skuas 

 (mostly from Handbook) 



Black-headed gull (O. Heinroth) about 40 days 



Common gull do. ,, 30 



Herring-gull do. ,, 42 



British lesser black- back (R. H. Brown) ,, 32 



Great black-back (O. Heinroth) „ 50 



Kittiwake (F. C. R. Jourdain) „ 35 



Great skua (W. E. Glegg) „ 42-49 



Arctic skua (W. E. Glegg) „ 28-35 



Long-tailed skua (A. Pedersen) „ 21 



