FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 169 



gulls flew along the ledges boldly, hunting eggs in a business- 

 like manner. The murres cackled and presented a pointed beak, 

 but the gull usually managed to snatch the egg of an absent 

 neighbor. 



Common-eider and gull colonies are often closely associated, 

 because of similar habitat preferences — an islet safe from blue 

 foxes. An eider nest and a gull nest are sometimes situated 

 only a few feet apart, apparently in good neighborly relations. 

 Yet the gulls seize the eggs or the downy young of the Pacific eider 

 when they have an opportunity. In fact, it appears that' the gulls 

 manage to devour an appreciable percentage of eider increase, 

 both in eggs and young. 



Other nesting birds may be thus preyed upon under favorable 

 circumstances. On Semichi Island, Scheffer and I were passing 

 a lake, when a common loon swam off at our approach, leaving 

 two downy young. A glaucous-winged gull swooped down, picked 

 up a young loon and flew off with it, pursued by another gull. 



Certain adult birds are also taken by gulls. On Semisopochnoi 

 Island, in a least auklet rookery, 137 glaucous-winged gull pellets 

 were collected and analyzed, with the following results: 



Least auklet 116 pellets 



Forked-tailed petrels 3 pellets 



Small fish V pellets 



Sea urchin 8 pellets 



Limpet 3 pellets 



On Gareloi Island we found gull pellets that contained both 

 least and crested auklets, and two fulmar eggs. 



Some of the bird material, especially that of the crested auklets, 

 probably was carrion left by blue foxes ; however, our observations 

 were not conclusive. 



The sea urchin is another important item in this gull's diet 

 throughout the entire Aleutian district. 



At Unalaska, on May 27, 1937, we saw a large flock of these 

 gulls, chiefly immature birds, feeding back in the hills ; apparently 

 they were pulling up small clumps of grass. Regurgitated ma- 

 terial consisted mainly of seeds, but we did not have time to make 

 a thorough study of this incident. 



Where the gulls depend on the tides for their food, they 

 naturally adapt their foraging periods to the time of ebb tide. 

 This was noted particularly in Izembek Bay. At Glen Island, 

 it was noted that fewer birds were present at the colony during 

 low tide; when the tide came in, the colony was in full force. 

 Incidentally, it seemed that by means of a division of labor, the 

 nests remained guarded while a part of the colony fed. 



