STERCORARIIDJE THE SKUAS AND JAEGERS. 213 



The Skua is a maritime bird of irregular and uncertain distri- 

 bution, but by no means common anywhere along the coasts of 

 North America. According to Captain J. W. Collins, 01 the 

 United States Fish Commission, whose knowledge of our sea- 

 birds is probably greater than that of any other person on ac- 

 count of his long connection with the cod-fisheries of the New- 

 foundland Banks, informs us* that this bird, the "Sea-hen" of 

 the fishermen, is occasionally seen on the fishing grounds at all 

 seasons, but is never abundant, one, two, or three birds, being 

 generally seen at a time, while on very rare occasions perhaps 

 half a dozen will gather round a vessel from which offal is being 

 thrown. He found them most common on the Grand Bank in 

 autumn, and in the fall of 1875 shot several fine specimens that 

 were used as bait. 



GENUS STERCORABUJS BRISSON. 



Stercorarius BEISS. Orn. v, 1760, 149. Type, Larus parasiticus LINN. 

 Lestris ILLIG. Prodr. 1811, 272. Same type. 



GEN. CHAE. Size medium (about that of Larus delawarensis and L. canus)', form 

 more graceful and slender than Megalestris; depth of bill through base less than half 

 the length of the mandible, measured along its side; tarsus decidedly longer than 

 middle toe and claw; middle pair of tail-feathers (in adults) projecting far beyond the 

 rest. 



This genus differs from Megalestris chiefly in the smaller size 

 and more slender, graceful form of its members, the increased 

 slenderness extending to all parts of the organization, as indi- 

 cated in the above diagnosis. 



Of the three known species, one differs considerably in form 

 from the other two, which are sometimes so much alike as to be 

 with difficulty distinguished from one another. Their differential 

 characters are as follows : 



A. Culmen 1.45 or more, tarsus 2.00 or more, wing usually more than 13.50; lengthened 



middle tail-feathers broad and rounded at ends. 



1. S. pomarinus. 



B. Culmen less than 1.45, tarsus less than 2.00, wing usually less than 13.50; lengthened 



middle tail-feathers narrow and pointed at ends. 



2. S. parasiticus. Length of nnsal shield or cere, from base of unguis to frontal feath- 

 ers, decidedly greater than from the former point to the tip of upper mandible. 



3. S. longicandus. Length of nasal shield from base of unguis to frontal feathers 

 not greater than distance from former point to tip of upper mandible. 



* The Auk i, 1881. p. 238. 



