6o DwiGHT, Moults and Plumages of Gulls and Terns. \J]tn 



and a gray back are acquired. The feet in adults remain flesh- 

 colored. 



9. Fourth Winter Plumage acquired by a complete third post- 

 nuptial moult. This is practically like the third winter or later 

 winter plumages, and although the age of birds after the second 

 postnuptial moult can only be inferred from their plumage, it is 

 probable that the white spots of the primaries, especially of the 

 first, increase with age. The size of the bill and the whiteness of 

 the head in winter also increase. As a progressive increase in 

 these matters can be demonstrated at the time of three moults, it 

 is logical to assume, within certain limits, a continued increase, 

 and so in older birds we would expect a fusion of the two terminal 

 areas of white on the first primary. The presence of a divided 

 white area is the chief character on which the American subspe- 

 cies s7nithsonianus rests, and unless differences from the European 

 birds can be found in all of the stages of plumage just indicated 

 the separation rests on a very slender basis. Is the European 

 oird always marked by one white area .' It is not difficult to pick 

 out a series of American birds showing all gradations from a first 

 primary with a small white spot to one that ends in a broad dash 

 of white, and I believe that the scarcity of the whiter-tipped speci- 

 mens is due rather to the diminishing numbers of older birds and 

 their increasing wariness than to the straggling to America of Old 

 World birds. 



The question of age has not been sufficiently taken into account 

 by the systematists who have attached undue importance to the 

 spots and spaces of white and gray found on the wings of gulls. 

 There is no question but that there is a progressive increase, with 

 age, of white or gray areas in many species. The white spot of 

 the first primary grows larger in a number of species at successive 

 moults, and in many of the species the blackness of the feather 

 shaft through it is gradually lost. The size and proportions of 

 the bill also vary with age, while its color varies both with age 

 and with season, being dark in winter and usually yellow in sum- 

 mer. These matters should be weighed in studying the affinities 

 of the gulls. The larger ones may be conveniently divided into 

 three classes : those with black primaries, those with white, and 

 those with gray. In all three the sequence of plumages and moults 



