94 



ORNITHOLOGICAL EXPLORATIONS. 



numbers. In the colonies breeding on Bering Island not a single light 

 bird was to be seen, and the same was the case at the rookeries on the 

 northern part of Copper Island, for example, that close to the village. 

 At Glinka, near the southern extremity of the latter island, were found 

 a few small white colonies, but the percentage of the light- colored birds 

 was quite trifling, as I estimated it to be between 1 and 5 per cent. The 

 accounts of the birds taken in Kamtschatka and the Kurile Islands are 

 exceedingly meager, but indicate the dark phase as far as they go. 



(5.) In the Atlantic occurs a smaller race, F. glacialis minor Kj^rb., 

 besides the typical F. glacialis, whicli also has two phases. In the Pacific 

 another race occurs, which is fairly distinguishable from F. glacialis 

 glupischa, viz, F. g. rodgersii, characterized by its pale color and the great 

 amount of white. The latter seems to be a northern form, apparently 

 without any dark phase. 



The question now arises as to the real nature of the two phases. A 

 name is easily found and we may take our refuge under the shelter of 

 "dichromatism." This does not solve the question, however, which is 

 a most interesting one. What is dichromatism, its causes, its nature? 

 We have one kind in rai)torial birds, especially the owls, another among 

 the herons; a third kind is that of Stercorarius parasiticus, and we 

 may in this connection also quote the Arctic Fox ( Yulpes lagopus), be- 

 sides many other cases, but only future studies of the living birds will 

 enable us to obtain satisfactory results. 



Hat of specimens collected. 

 WHITE PHASE. 



DARK PHASE. 



Copper Island [ June 8, 1882 



Bering Island i May 4, 1883 



Copper Island July 5, 1883 



No. 92908. — Iris dark brown. Bill light greenish lemon-yellow, the middle of each piece or lamella 

 oranfie brownish, and the edges blackish : aloiiK tomia of lower mandible and chin-angle flesh color. 

 Eye-ring dark brownish gray. Feet whitish with a faint greenish tinge; joints, tarsus behind and 

 toes below, outer web and anterior border of inner web blackish brown ; nails horny white. Stomach 

 tilled with feathers. Exceedingly lean. 



