184 NORTH AMERICAN FAUNA 61, FISH AND WILDLIFE SERVICE 



remained static. There were the numerous murres and gulls, and 

 about the same number of nesting eagles and falcons. 



On Bogoslof Island, in 1937, we watched the glaucous-winged 

 gulls seizing eggs and young murres, apparently on a large scale. 

 In 1938, Scheffer remarked in his field report, "On the island 

 [Bogoslof], more murres were noted this year resting on the cliffs 

 or vertical bluffs where the party landed in 1937 and 1938." 

 Apparently, the colony was not only holding its own, but it may 

 have been increasing. The bluffs mentioned by Scheffer were not 

 in the main nesting grounds, and were not typical, nor per- 

 haps as favorable, in some respects. Possibly these bluffs were 

 in reality an overflow area in a crowded bird population. 



R. A. Johnson (1938) has presented a detailed study of preda- 

 tion of gulls in murre colonies, based on his own specific studies 

 of Atlantic murres and great black-backed gulls, as well as re- 

 ports of other ornithologists. One factor is disturbance by a 

 human intruder, which makes the murres more vulnerable to 

 attack by gulls. Johnson believes that the fear response by the 

 murres is very important, and that it is a colony response. Once 

 a decline in a murre colony is begun and the colony becomes con- 



Figure 32. — Colony of Pallas's thick-billed murres on nesting cliffs of 



Bogoslof Island. 



