Sabine's GuU 21 



and inner web along the shaft of the three or four outer primaries, 

 and a black subterminal bar across the tail with a narrow terminal 

 band of white. 



Distribution. — Breeding from Manitoba northwards to Hudson Bay 

 and Alaska ; on migration both along the coasts and in the interior 

 of the United States and the coasts of western Mexico. 



In Colorado Bonaparte's Gull is an occasional visitor on migration, 

 chiefly in the fall. It has been taken about half a dozen times on 

 the plains at the eastern bases of the mountains from Pueblo to Fort 

 Collins in October and November, and by Carter on the spring migration 

 in Middle Park. The records are : Pueblo, November 15th, H. W. 

 Nash (Cooke), near Colorado Springs (Aiken coU.), near Denver on 

 three occasions in October and November (H. G. Smith), Barr Lake, 

 one killed but not preserved, fall of 1907 (Hersey), and Fort Collins 

 (Cooke). 



Genus XEMA. 



Resembling the smaller forms of Larus, with hooded head in summer 

 and with a slender bill, but the tail distinctly forked though not for 

 more than the length of the tarsus. 



One species only. 



Sabine's Gull. Xemasabini. 



A.O.U. Checklist no 62— Colorado Records — Ridgway 79, p. 232 ; 

 W. G. Smith 89, p. 176 ; Morrison 89, p. 147 ; H. G. Smith 96, p. 48 ; 

 Cooke 97, pp. 61, 155, 193 ; Henderson 03, p. 234 ; 07 p. 198 ; 09, p. 225. 



Description. — Adult — Head all round deep slaty, bordered by a 

 narrow ring of velvety black ; lower part of neck, tail, under-parts, 

 inner primaries, most of secondaries and greater coverts white ; mantle 

 and the inner secondaries slaty-blue ; outer primaries black, with the 

 half of the inner web away from the shaft and tips white ; eyelids 

 orange, bill black on the basal, yellow on the apical half, feet black. 

 Length 13 ; wing 10'75; tail to fork 3*75, to longest feather 5-0; culmen 

 1-0 ; tarsus 1-25. 



In winter the head and neck are white with a little dusky on the 

 ear-coverts and back of the head. Young birds are like the winter 

 birds, but the back of the head and neck as well as the mantle is slaty, 

 most of the feathers edged and tipped with whitish ; the outer primaries 

 are more black and the white tips are small or wanting ; the tail has 

 a subterminal bar of black, becoming narrower towards the outer 

 feathers, and is less forked ; the bill and legs are flesh-coloured and 

 dusky, and the dimensions are smaller — wing 10-25. 



