252 BRITISH BIRDS. 



from the point of view taken by Giinther when he proposed the geogra- 

 phical regions for fishes, divisions which Boulenger has since ascertained 

 to be applicable also to Batrachians. 



Genus STERNA. 



The genus Sterna was recognized by Linnaeus in 1766, in the 12th 

 edition of his ' Systema Naturae/ i. p. 227. The Arctic Tern, Sterna 

 arctica, is generally recognized as the type of the genus, though it would 

 be very difficult to assign any reason for the preference. 



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

 Sabine's Gull) by their more or less forked tails. They have long slender 

 bills, the curvature of the profile of the upper mandible scarcely varying 

 from base to tip. They have long wings, short tarsi, and small feet. 



This genus may be regarded as cosmopolitan; it contains about fifty 

 species. Eleven of these have been considered by Saunders to be suffi- 

 ciently aberrant to warrant their removal to other genera; but, as is usually 

 the case when Nature's natural divisions are interfered with, the subdivider 

 is obliged to fall back upon specific characters to diagnose his genera, and 

 consequently the eleven species require four genera for their accommodation. 

 It is only fair to say that other ornithologists have split up the Terns into 

 twenty or more genera. 



The Terns are found on inland lakes, but principally frequent the sea- 

 coast and the adjoining lagoons. They are remarkable for the singular 

 gracefulness of their flight; and may be said almost to live in the air. 

 Upon the ground they walk clumsily, but they can swim with ease. They 

 are more or less gregarious at all seasons. They feed on small fish, crus- 

 taceans, insects, &c., which they secure whilst hovering above the water or 

 by a sudden plunge into it. Their notes are harsh. They make little or 

 no nest, depositing their eggs in a slight depression in the sand or shingle, 

 or amongst marine vegetation. 



The following artificial key to the British species of Terns will enable 

 the student to name them in any plumage : 



A. Fork of tail less than 1 inch deep ; length of wing from 7 to 10 



inches, 

 a. Under wing-coverts black S. LETJCOPTERA*. 



* The White-winged Black Tern is the most distinct of all the Terns in summer 

 plumage, no other species having the under wing-coverts black. Young birds and adults 

 in winter plumage are much more difficult to determine. In these plumages there does 



