NATATORES. 418 



latitude. Its eggs, two, or sometimes three, are deposited on a tuft of dry 

 grass, upon sand, or among stones, and are hatched principally by the heat of 

 the sun, the bird sitting upon them only during the night, or in cold weather. 

 It is very clamorous when any one approaches the spot, and flies towards him, 

 plunging close to his head, and rising again with great velocity. In these evo- 

 lutions its forked tail is sometimes spread out, but more generally closed, so as 

 to appear pointed. It feeds principally on small fish, which it picks up from 

 shallow water, on the wing. The length of its wings and tail, and the shortness 

 of its legs, render progression on the ground inconvenient, and it is seldom 

 observed to alight. It passes the winter to the south of the United States. 



DESCRIPTION 



Of a male killed on the banks of the Saskatchewan, July 18, 1827. 



Colour. — Upper surface of the head and the nape pitch-black. Back of the neck, back, 

 wing coverts, and secondaries, pearl-grey, inclining to blue, the tips of the latter fading to white. 

 The exterior web of the first primary a stripe on its inner web next the shaft, and the tips 

 and inner margins of the others blackish-grey; this colour, glossed with shining ash-grey, on 

 the remainder of the quills. All the quill-shafts, the rump, under eyelid, inferior plumage, 

 and insides of the wings, white ; the breast, belly, and flanks, slightly tinged with grey. 

 Tail and its coverts pearl-grey ; outer feather white exteriorly ; dark-grey near its point 

 interiorly. Bill orange-coloured, tipped with blackish-brown. Legs scarlet. 



Form, typical. — Wings much pointed, equalling the tail in length. Tail deeply forked, 

 the exterior feathers being four inches longer than the central pair, and tapering almost to a 

 point. Thighs naked for seven lines. Scales of the tarsi delicate ; their divisions not very 

 perceptible. Middle toe, excluding its nail, shorter than the tarsus. 



Dimensions. 



Inch. Lin. Inch. Lin. Inch. Lin. 



Length, total . 16 3 Length of bill to rictus . 2 2 Length of inner toe . .0 6^ 



„ of tail . .69 „ of tarsus . .011 „ of hind toe . 2| 



,, of wing . . 10 6 „ of middle toe . .09 ,, of its nail . .0 1J 



„ of bill above . .16 „ of middle nail . 4^ — R. 



Note. — English specimens of Sterna hirundo differ from the above in the outer web of the exterior tail-feather 

 being blackish-grey ; the inner webs of all the tail feathers, and the whole of their coverts, white. The blackish grey 

 of the quills is more extended. The tarsus is more slender and two lines shorter than in the American bird. Further 

 observation must determine whether these differences are constant. They exist in several specimens from both 

 countries, which I have examined ; and the peculiarities of the Hudson's Bay bird attracted the attention of Forster. — R . 



