THE TERNS, SKIMMERS, AND GULLS 



2281 



Skimmers 



The remarkable birds known as skimmers, or scissor bills, con- 

 stitute a subfamily {RhynchopinaT) t distinguished not only from 

 the terns (which they other- 

 wise resemble), but likewise 

 from all other birds, by the 

 peculiar structure of the beak, 

 this organ being elongated and 

 compressed to a knife-like form, 

 with the lower mandible consid- 

 erably longer than the upper 

 one, which is freely movable. 

 The single genus of the sub- 

 family is represented by three 

 species, of which the black 

 skimmer (Rhynchops nigra}, 

 distinguished by its dark beak, 

 is North American, while the 



yellow-beaked skimmer (R. albi- BLACK SKIMMER> 



collis] is Indian, the third species 



inhabiting the Nile and Red Sea littoral. The American species has been observed 

 flying close to the water, with the lower half of the beak immersed beneath the sur- 

 face, doubtless searching for food. 



The gulls proper, as distinguished from the other members of the 

 order, form the third subfamily (Larinte) of the typical family, the 

 great majority of them belonging to the genus Larus, although the kittiwake and 

 an allied species from the North Pacific are separated as Rissa; while Sabine's gull 

 and a kindred but very rare form from the Galapagos islands constitute the genus 

 Xema; and Ross's gull (Rhodostetkia rossi} and the ivory gull (Pagophila eburnea} 

 respectively represent distinct generic types. As a subfamily, the gulls are charac- 

 terized by the upper mandible of the beak being longer than the lower one, over 

 which its tip is bent down; while the tail is usually squared, although in one genus 

 it is forked, and in a second wedge shaped. Some of the smaller gulls, like so 

 many of the terns, assume a dark head and neck in the summer plumage. 



Sabine's gull (Xema sabinei}, together with the Galapagos fork- 

 r Gulls tailed gull (X. furcatum}, may be at once distinguished by the forking 

 of the tail, a characteristic in which they agree with the great ma- 

 jority of the terns, as they also do in the assumption of a dark head during the 

 breeding season. Not a very uncommon straggler especially in the immature 

 state to the British Islands, Sabine's gull breeds in Arctic America and Siberia, 

 generally in company with the Arctic tern, two eggs being laid by the female on 

 the bare ground. Of the second and larger species but little is known, only a few 

 examples having found their way into European collections. 



As the forked tail serves to distinguish the members of the last 

 genus, so the single representative (Rhodostetkia rossi} of the present 

 one is equally well demarcated by the wedge-like contour of the same appendage. 



Gulls 



Ross's Gull 



