290 THE NESTS AND EGGS OF 



Incubation lasts a month, but whether both sexes or 

 which performs the duty is apparently unknown. 



Diagnostic characters : Unfortunately I know of 

 no character by which the eggs of the Glaucous Gull 

 can be distinguished from those of the Herring Gull or 

 from small examples of those of the Great Black-backed 

 Gull. They require careful identification. 



Family LARID^. Genus Larus. 



Sub-family TARING. 



GREAT BLACK-HEADED GULL. 



Larus ichthyaetus, Pallas. 



(British : Very rare abnormal spring migrant.) 



Number of Broods unknown. Laying season, May and June. 



Breeding area : South-central Palaearctic region^ 

 and North-eastern Ethiopian region. The Great Black- 

 headed Gull breeds in Egypt, Cyprus, Palestine, on the 

 Seal Islands in the Caspian Sea, also on the low-lying 

 coasts of that sea Itself, northwards to the lakes of 

 Turkestan, South-western Siberia, Western Mongolia, 

 and Thibet. 



Breeding habits : But little is known respecting 

 the nidification of this Gull. It is a migrant in the 

 more northern portions of its range, reaching them for 

 breeding purposes in May or early in June. It breeds 

 on the low-lying coasts and islands as well as on the 

 banks of inland lakes. Of its pairing habits nothing Is 

 known, nor can I find that its nest has been accurately 

 described by any competent naturalist. 



