252 SEA-BIRDS 



The terns, like the gulls, may be divided conveniently into these two 

 categories: one containing the strictly marine species, nesting largely 

 on sand, shingle or rock, and chiefly white, with grey back and 

 black crown; and the other containing those species, some of them 

 black or black-winged, and black-backed, which nest on salt- or 

 fresh- water marshes. The latter in the North Atlantic region include 

 the gull-billed tern Gelochelidon nilotica, Caspian tern Hydroprogne 

 caspia, Forster's tern Sterna forsteri, black tern Chlidonias nigra, whiskered 

 tern C. hybrida, and white-winged black tern C. leucopterus. 



Terns are gull-like in their habits, but their longer wings and long, 

 usually forked, tails, give them a distinctive appearance. Their flight 

 is more buoyant and graceful. Because the wings appear to pass 

 through a greater arc in their slow measured beating, the flight may 

 not seem so effortless, and it is also less gliding than that of the gulls. 

 The general impression is of a light hovering progress, and the synonym 

 "sea-swallow," often applied to the tern, is only appropriate in as far 

 as the long wings and tail of the tern resemble those of the swallow. 



Terns were formerly killed for the millinery trade, but are now 

 protected in English-speaking countries. As already described in 

 chapter 3, p. 84 the little tern was taken in "incredible numbers" and 

 almost exterminated along the eastern U.S. coast by collectors for 

 this trade, in Audubon's time. From about 1800, for nearly a hundred 

 years, the feathers of this tern and many other species of birds, includ- 

 ing the roseate tern, were in demand, wings and whole skins being 

 used to decorate women's hats. 



All terns are considerable migrants, the arctic tern (see p. 142) 

 greatest of all, breeding as far north as there is land in the Arctic, 

 and migrating as far south as there is open water in the Antarctic; 

 in both polar seas arctic terns may fish among pack-ice, and rest on 

 ice-floes head to wind, especially in their antarctic winter quarters 

 (Falla, 1937). Thus, although they are called arctic terns, these birds 

 enjoy more hours of daylight (eight summer months in the year) 

 than the tropical species, by wintering in the southern summer. The 

 majority of terns arrive at their breeding ground later than the gulls. 

 The vanguard appear in March in the British Isles, with main arrivals 

 in April and May; but they may be a month or six weeks later in the 

 High Arctic. Like gulls, they roost at first away from the actual nesting 

 site, only settling down to sleep in the breeding ground a few days 

 before the eggs are laid. As the sexes are superficially alike it has not 

 yet been established whether the single birds which are sometimes seen 



