BONAPARTE'S GULL. 133 



their wings more sedately. I found the adult birds in moult in August. 

 Although their notes are different from those of all our other species, being 

 shriller and more frequent, I am unable to represent them intelligibly by 

 words. 



Since I began to study the habits of Gulls, and observe their changes of 

 plumage, whether at the approach of the love season, or in autumn, I have 

 thought that the dark tint of their hoods was in the first instance caused by 

 the extremities of the feathers then gradually changing from white to black 

 or brown, without the actual renewal of the feathers themselves, as happens 

 in some species of land-birds. At Eastport, I had frequent opportunities of 

 seeing the black-hooded males copulating with the brown-hooded females, so 

 that the colour of the head in the summer season is really distinctive of the 

 sexes. I found in London a pair of these birds, of which the sexes were 

 distinguished by the colour of the head, and which had been brought from 

 Greenland. They were forwarded by me to the Earl of Derby, in whose 

 aviaries they are probably still to be seen. 



This is certainly the species described in the Fauna Boreali-Americana 

 under the same name; but it is there stated that the females agree precisely 

 with the males, their hood being therefore "greyish-black;" which I have 

 never found to be the case. As to the Larus capistratus of Bonaparte's 

 Synopsis, I have nowhere met with a Brown-headed Gull having the tail 

 "sub-emarginate;" and I infer that the bird described by him under that 

 name is merely the female of the present species. 



Brown-masked Gull, Larus capistratus, Bonap. Amer. Orn., vol. iv. Female. 



Larus capistratus, Bonap. Syn., p. 358. 



Larus Bonap artii, Bonapartian Gull, Swains, and Rich. F. Bor. Amer., vol. ii. p. 425. 



Bonap artian Gull, Nutt. Man., vol. ii. p. 294. 



Bonapartian Gull, Larus Bonapartii, Aud. Orn. Biog., vol. iv. p. 212. 



Adult, 14i 32^. 



Extremely abundant in winter, on the coast of Florida. Equally plentiful 

 in spring, along the coasts of the Middle and Eastern Districts, especially in 

 the Chesapeake. Breeds from the Bay of Fundy to high latitudes. Not 

 uncommon in autumn, on the Great Lakes, and the Ohio and Mississippi. 



Adult Male in spring plumage. 



Bill shorter than the head, nearly straight, slender, compressed. Upper 

 mandible with its dorsal line straight to the middle, then curved and 

 declinate, the ridge narrow, the sides slightly convex, the edges sharp and a 

 little inflected, the tips narrow but rather obtuse, with a slight notch on each 

 side. Nasal groove rather long and narrow; nostrils in its fore part, 

 longitudinal, sub-medial, linear, pervious. Lower mandible with a slight 



