STERCORARIUS. 345 



Genus STERCORARIUS. 



The Skuas were included by Linnaeus in his genus Larus ; but in 1760 

 Brisson adopted the genus Stercorarius for their reception in his ' Orni- 

 thologia/ vi. p. 149^ Richardsou^'s Skua^ S. richarclsoni (the Stercorai'ius 

 stercorarius of Brisson), being the type. 



The Skuas may be distinguished from the Gulls and Terns (except from 

 Ross's Gull) by their cuneiform tails. From both these genera the shape 

 of the bill and the position of the nostrils are still more distinctive. The 

 upper mandible is vaulted like that of the Plovers, nearly straight for two 

 thirds of its length, but ends in a strongly curved raptorial hook; the 

 nostrils ai-e partially covered by a horny shield, which leaves the entrance 

 to them diagonal. The bills of the Skuas, as well as their cuneiform tails, 

 bear a superficial resemblance to those of the Petrels, but these two groups 

 are said to be otherwise widely separated. 



Only six species of Skua are known, four of which breed in the Arctic 

 Region, one of the four being represented by two nearly allied species in 

 the southern hemisphere, breeding on the confines of the Antarctic Region. 

 The four northern species are all included in the British list, two of them 

 breeding within our confines, and the other two visiting our shores on 

 migration. 



The Skuas resemble the Gulls in many of their habits, but they are 

 more bold and predacious birds, obtaining much of their food by robbing 

 the Gulls and Terns of their hard-earned spoils, or even preying on birds, 

 small mammals, and eggs ; they also eat insects, crustaceans, &c. In 

 their flight, mode of progression on laud and sea, in their notes, nests, 

 and eggs, and the places they frequent, they do not differ in any very 

 important respect from the birds in the preceding genus. 



VOL. III. 



2a 



