VO, 'l9l9 XVI ] Dwight, Larus hyperboreus. 245 



"somewhat" and Dr. Oberholser "decidedly" darker, I can only 

 say that my series fails to support either of these statements. I 

 find that if comparison of like stages of plumage be made, birds 

 from Greenland are quite as dark as Alaska specimens and con- 

 versely Alaska birds are as pale as those from Greenland. It 

 is, perhaps, a matter of more than passing interest that the major- 

 ity of adult Greenland birds in the collections I have seen are in 

 worn faded plumage while most of the Alaska material is in fresh 

 dark plumage. One might easily get the impression that the 

 darker birds represent a race unless due allowance is made. 



It may not be generally known that the adult Glaucous Gull 

 moults twice in the year, a complete postnuptial moult beginning 

 toward the last of July and extending over nearly two months and 

 a prenuptial in March and April which involves most of the body 

 feathers but not the wings nor the tail. Between moults the 

 mantle fades and looks even paler than it is in color because of 

 the worn and whitened feather edges. There is some individual 

 variation in the depth of color in freshly moulted specimens, 

 whether from Greenland or Alaska, but both may be equally dark 

 and they may become equally pale after the lapse of a few months. 

 I have examined birds taken nearly every month in the year and 

 I am at a loss to understand how Dr. Oberholser finds a " decidedly 

 darker" race unless he has unwittingly compared birds of unlike 

 stages of plumage. 



2. As for size, this is a question of relative dimensions that 

 permits some latitude of opinion, so that a new presentation of 

 the facts seems desirable. 



My early table of measurements (Auk, XXIII, 1906, p. 28) 

 based on 31 adults (14 of them males and 17 females) is accepted 

 by Dr. Oberholser " except for dimensions of the bill which have 

 been remeasured for the present use." I have reproduced all of 

 these measurements by the graphic method (Fig. 1) and anyone 

 may see, almost at a glance, what the variations of size in the 

 Glaucous Gull actually are. The diagrams are drawn to scale, 

 the upper horizontal line representing the actual size of the largest 

 specimens, males and females, the middle line the mean or average 

 size and the lower line the smallest specimens. The oblique solid 

 lines represent hyperboreus, the broken lines " barrovianus" and 



