776 A PRACTICAL HANDBOOK OF BRITISH BIRDS. 



Average of 41 eggs, 60.45 X 43.27. Max. : 69.3 X 41.5 and 60 X 46.2. 

 Min. : 53x40.5 and 59.7x40 mm. Breeding -season. — Latter part 

 June or early July. Incubation. — Apparently by both sexes. 

 Period unknown. Single brooded. 



Food. — In breeding -haunts mainly droppings of mammals (seals, 

 walruses and bears), also carcasses of killed mammals (chiefly flesh 

 and blood, less frequently blubber), fish, Crustacea, mollusca 

 (pteropoda, etc.), and larvse of diptera. 



Distribution. — British Isles. — Rare vagrant. About sixty. Most 

 frequent Shetlands and Orkneys, but has occurred many counties 

 Great Britain (Yorks., seven), and five in Ireland. From autumn 

 to spring and as late as June. 



Distribution. — Abroad. — Breeds in high arctic latitudes around 

 North Pole, wintering south as far as north France, Denmark, Lake 

 Geneva (once), British Columbia, Lake Ontario and Long Island in 

 America. 



Genus STERCORARIUS Briss. 



Stercorarius Brisson, Orn., i, p. 56 (1760 — Type by tautonymy 

 stercorarius —Larus parasiticus L., according to vol. VI, p. 149). 



Differs so much from other Laridce as to be generally recognized 

 as subfamily, Stercorariince, or even as separate family. Bill 

 reminding one of Tubinares, upper consisting of four fairly distinct 

 parts, a " cere," two lateral portions, and the distal part, which is 

 strongly hooked. Tarsus and feet rough, scutes and reticulations 

 being rather prominent ; claws strong, hooked, sharp. Many 

 authors separate two genera, Stercorarius with rather elongated, 

 and Megalestris larger and with very little elongated middle 

 rectrices ; this, however, is not logical, as the other species are about 

 equally different. The differences are in our opinion not such as to 

 demand more than one genus, but if more than one are admitted, 

 we must have four : Stercorarius, Labbus, Coprotheres, and Cataractes 

 ("Megalestris"). 



Key to species of genus Stercorarius. 



(Adults only.) 



, f Much larger, bill over 45, wing over 380 mm. . S. skua, p. Ill 



\ Much smaller, bill under 4 5, wing under 380 mm. 2 



f Middle rectrices very long and pointed, more than 

 9 J three times as long as rest of tail . . . S. longicaudus, p. 787 



) Middle rectrices not quite twice as long as rest of 



(_ tail 3 



f Middle rectrices at tip narrow and pointed . S. parasiticus, p. 783 



3-^ Middle rectrices not considerably narrowed nor 



^ pointed at tip S. pomarinus, p. 77*> 



