30 Dwight, The White-winged Gulls. \_f&n 



young birds at the limited postjuvenal moult in November or 

 later reassume some mottled feathers, likewise at the prenuptial 

 in March, and even at the first postnuptial in August there are 

 often many evidences of immaturity that persist throughout a 

 second year. The adults undergo a complete postnuptial moult 

 in August or September and a partial prenuptial moult in March 

 or April. The details of plumage and of moult may be better 

 discussed under the separate species, and we may now turn at 

 once to them. 



Larus glaucus. Glaucous Gull. 



This large circumpolar species breeds within the Arctic circle, 

 moving southward in winter along the shores of both the Atlantic 

 and the Pacific oceans, sometimes nearly half way to the equator. 

 Knowledge of its plumages are derived from the material brought 

 by Arctic expeditions and from winter specimens. I have ex- 

 amined an even 200 of these birds, over 50 of them from Alaska, 

 the home of the so-called 'Larus barrovianus,' the series also 

 including over a dozen of the pure white phase known as 'Larus 

 ludchinsii,' probably the 'arcticus' of earlier w T riters. The plum- 

 ages of this species are too well known to require careful descrip- 

 tion, but the plumage changes in connection with the moults have 

 never been thoroughly described. The sequence is as follows: 



Natal Plumage. — The chicks are thickly covered with a soft, 

 dingy white down with large brownish gray spots clouding the 

 upper surface, especially about the head. Hatching in June, 

 before July is spent, they are well advanced into the next plumage, 

 the flight-feathers of which are among the first to appear. 



Juvenal Plumage. — August or early September finds birds 

 wholly in the brown barred or mottled plumage, of which the 

 flight-feathers and the tail are retained for a full year, the body 

 plumage and some of the lesser wing-coverts being partially 

 renewed at two periods of moult, the postjuvenal in November 

 or later and the prenuptial beginning often as early as the end 

 of February. Birds may be found moulting at any time between 

 October and May, and it may possibly turn out that but one moult 

 takes place, but as the renewal of feathers is rather limited, and 



