246 Dwight, Larus hyperboreus. LApril 



the dotted lines Dr. Oberholser's remeasurements of the bill. 

 His "depth of bill" for " barrovianus" is the same as mine and 

 therefore cannot be separately plotted. He does not tell us from 

 what series he made the remeasurements that do not tally with 

 mine, but the figures suggest that it may have been a small one 

 and with an unusual proportion of very large and very small birds, 

 possibly wrongly sexed in some cases. 



The original series that I measured was composed of breeding 

 birds from Greenland and from Alaska which formed a small part 

 of the 200 specimens I had then gathered together for comparison. 

 Although they are now widely scattered, some of them (as well as 

 new specimens) are still either in my collection or in that of the 

 American Museum of Natural History. A reexamination and 

 remeasurement of them (68 in all, 39 being adults) confirms to a 

 surprising degree my earlier measurements and conclusions. 

 Individual variation is greater than the supposed subspecific values 

 and the overlapping of size is marked. Birds as large as these 

 Gulls, it must be remembered, may not be measured with unfailing 

 accuracy, especially when different persons attempt it, for speci- 

 mens are often greatly worn, the wings or tail are sometimes not 

 quite grown and often the feathers are bent and broken. It is 

 not unusual to find a variation of five to ten or more millimeters 

 between the right and left wing of the same bird, due to the make-up 

 of the skin, while tarsi and toes of opposite legs may be bent very 

 much out of shape in drying. Where such variation exists, one 

 may to advantage measure each wing or foot separately and strike 

 an average as I have done in many cases. 



Turning finally to the bill, I would call attention to the sketch 

 (Fig. 2) which shows the average adult bill of the male of hyper- 

 boreus contrasted with that of "barrovianus." When one realizes 

 that the variation in the bills of all female gulls is much greater 

 than that of the males and that young birds only very slowly 

 acquire adult dimensions, it becomes evident that "barrovianus" 

 is not "very readily recognizable by its usually smaller size and 

 particularly smaller bill." One may guess cleverly that large 

 birds belong to one race and small ones to another, but without 

 reference to the labels the guesses may be astray by a continent's 

 width. 



