NON-INDIGENOUS BRITISH BIRDS. 285 



but in some cases otherwise closely resemble them in 

 colour. They also bear a close resemblance to certain 

 varieties of those of the Common Gull, but the locality 

 should be sufficient to determine them, as that bird does 

 not breed within the same area. 



Family LARID.E. Genus Pagophila. 



Sub-family LARIN^E. 



IVORY GULL. 



Pagophila eburnea {Phipps). 



(British : Rare nomadic autumn and winter migrant.) 



Single Brooded. Laying season, June and early July. 



Breeding area : Extreme Northern Nearctic and 

 Palsearctic regions. The Ivory Gull is confined prac- 

 tically to the land in the North Polar basin during the 

 breeding season, and nests as far south as Franz-Josef 

 Land, Spitzbergen, Nova Zembla, Herald Island, the 

 Parry Islands, and Grinnell Land. 



Breeding habits : The Ivory Gull does not wander 

 much south of open water during winter, and retires to 

 the Polar regions as early as it can find food. Our in- 

 formation respecting the nidification of this Gull is only 

 of the most meagre description. Of its pairing habits 

 absolutely nothing has been recorded. It is apparently 

 gregarious during the breeding season. Its favourite 

 nesting places are lofty precipices above the sea, but in 

 some localities where such cannot be had, it resorts to the 

 sea-beach, or to a low island in the Polar Sea. It appears 

 sometimes to nest in company with allied birds, such as 



