SUPPLEMENT TO BIRDS OF ESSEX COUNTY 33 



The recognition of a white-winged gull in the field is, with a little practice, 

 not difficult, and one may often with the naked eye alone pick one out in a flock 

 of Herring Gulls. The more difficult thing is to distinguish between the dif- 

 ferent species of white-winged gulls. It is perfectly possible, however, if the 

 observer is careful and accurate, to identify with certainty a Glaucous, an Iceland, 

 or a Kumlien's Gull without resort to shooting. The limited dark tips to the 

 wings in Kumlien's Gull may be overlooked if one is not careful, but once seen 

 they distinguish this gull from any others. The mantle of the adult is a lighter 

 gray blue than in the Herring Gull. 



The real difficulty comes in distinguishing the Glaucous from the Iceland 

 Gull, but once the distinguishing points are mastered, this difficulty disappears. 

 Size alone is deceptive and is unreliable in distinguishing these two birds, espe- 

 cially in the absence of other birds for comparison. The Glaucous Gull is gen- 

 erally the size of the Great Black-backed Gull but may be somewhat smaller, and 

 often looks no larger than a Herring Gull. It may be said here in parenthesis, 

 that the Great Black-backed Gull, although often looking much larger than the 

 Herring Gull with which it associates, not infrequently appears the same size. 

 The Iceland Gull is slightly smaller than the Herring Gull, but the difference in 

 size between the Iceland and the Glaucous Gull often disappears in the field. 

 In fact it has been stated that the large male Iceland Gull equals in size the small 

 female Glaucous Gull. Where the difference. in size is noticeable this serves to 

 distinguish the two species. A surer field-mark, however, is the size of the bill, 

 head, and neck. The Iceland Gull has a small dove-like head, a small neck which 

 is held up straight as the bird sits on the water, and a small bill. Dr. Dwight^ 

 gives the average length of the bill of the adult Glaucous Gull as 63 mm., of the 

 Iceland Gull, 42 mm., a difference of 21 mm., or about three-quarters of an inch. 

 Most of the Glaucous Gulls seen on the coast in winter are immature, occasionally 

 pure white, the hutchinsii type,^ but usually more or less mottled with brown or 

 chocolate. According to Dwight the pearl-gray mantle of the adult does not as 

 a rule appear until the third winter and coincidently the color of the bill changes 

 from dark to yellow. Mr. Francis H. Allen' has given an excellent review of the 

 white-winged gulls seen near Boston and along the Essex County coast with an 

 account of their field-marks. 



The Glaucous Gulls, although sometimes seen alone, are generally associated 

 with Herring Gulls. At times I have seen Great Black-backed, Herring, Iceland, 



1 Dwight, J., Jr. Auk, vol. 23, p. 28, 1906. 



2 1 was in error when I stated in the original Memoir that " in old age the bird is almost 

 pure white." In this I had followed previously published statements. 



2 Allen, F. H. Auk, vol. 25, p. 296-300, 1908. 



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