Vol. XXIII 

 1906 



Dwight, The White-winged Gulls. 29 



than through the base" — on which the species was founded 

 proves to be mythical. It is true that the largest specimens of 

 barrovianus never quite reach the dimensions of the largest glau- 

 cus, but overlapping of size is so considerable, even when careful 

 comparison of sexes is made, that without first reading the labels 

 one cannot, except in a very few cases, tell whether a bird is from 

 Greenland or from Alaska. The variation in the size and shape 

 of the bill in gulls is very great, and a few millimeters difference 

 in wings that are as long as one's arm is hardly ground on which 

 to rest a subspecies, much less a full species. In view, therefore, 

 of these facts, I would urge the removal of barrovianus from the 

 North American list, the name becoming a synonym of glaucus. 



Measurements, while dry, are instructive, although often posi- 

 tively misleading when derived from very small series. My table 

 shows that the individual variation within each species is over 

 7 %. It also shows that kumlieni is the size of leucopterus with 

 a bill 6 % larger, and nelsoni 16 °fo larger than kumlieni with a 

 bill 24 % larger, a species, in fact, just about the size of glaucus. 



Before discussing the plumages of the different species it may 

 be well to draw attention to characters that are shared in common. 

 Adults in breeding dress are white birds with white tails and with 

 white tips to the flight-feathers, the gray of the mantles shading 

 into the primaries, which are lighter in glaucus and leucopterus, 

 darker in glaucescens, and have slaty markings in kumlieni and 

 nelsoni; in winter the white heads and breasts are more or less 

 clouded with smoky gray. The bills at all seasons are bright 

 yellow with a vermilion red spot at the angle of the lower mandible, 

 neither the yellow nor the red losing all its color even in old dried 

 specimens. The legs and feet are flesh colored, drying to various 

 shades of brown and yellow. The eyelids are yellow and the 

 irides a pale yellow. Young birds are in general appearance 

 pale brown and white, or gray, usually with a mottled or 'watered' 

 effect, the primaries brown or gray, often white, and with no mot- 

 tling or very little of it at the apices. The bills are brownish 

 black paling to buff at the base. The legs and feet are flesh colored. 

 The irides are brown. 



I will not attempt to outline here the intermediate stages of 

 plumage through which each species goes. Suffice it to say that 



