462 NATATORES. STERNA. 



sent the fisirostral tribe of the Insessores, have a form and 

 organization admirably suited to their particular economy. 

 Being destined to pass the greater part of their existence in 

 the air, their wings are of great extent, the tail long, and in 

 general deeply forked (a shape possessed by most birds 

 gifted with extraordinary power of flight), the body small 

 and compact, the legs short, and with small feet, not calcu- 

 lated to advance their progress in swimming, but sufficient 

 for their support when occasionally reposing on the water. 

 Such of the species as frequent the ocean subsist upon the 

 fry and the smaller kinds of fish, which they take from the 

 wing, by precipitating themselves upon such as rise within 

 a certain distance of the surface of the water. In this act 

 they descend with astonishing rapidity and force, and are 

 often buried beneath the waves for several seconds. Others, 

 more frequently found upon rivers and fresh- water lakes, in 

 addition to fish, prey upon libellulae, and other aquatic in- 

 sects. The distribution of the different species is very ex- 

 tensive, as they are found in all quarters and climates of the 

 world. They are subject to a double moult, but the vernal 

 change is confined to the region of the head, and the plu- 

 mage of both sexes is precisely similar. The young, until 

 after the first or second general moult, differ from the old 

 birds. During the season of reproduction they congregate 

 in large bodies, nestling closely together, generally upon the 

 shingle, or lower parts of the islets they frequent. Their 

 eggs are three or four in number. By the near affinity of 

 the Gull-billed Tern (Sterna Anglica) to some of the lesser 

 species of dark-headed gulls, their connection with the genus 

 Larus is evidently traced. 



