THE BIRDS OF THE PRIBILOF ISLANDS. 



369 



DISTRIBUTION OF THE FAMILY ALCIDAE IN NORTH AMERICA. 



I have prepared the above table for the purpose of illustrating the great diflfer- 

 ence between the two sides of North America as represented in this order,^ But one 

 form is found on both sides, and this a high northern species which can readily in a 

 very mild season pass from one side to the other. The ^Icinae are distinct, but have 

 hardly been separated for any great length of time. The characters of the others 

 indicate, however, that when the present boreal climate was milder a barrier existed to 

 prevent dispersion. 



THE MIGRATION OP PRIBILOF BIRDS. 



I can do little more than hint at the facts, phases, and factors that are concerned 

 in the bird migration of this portion of Bering Sea. For the true migrants (not sum- 

 mer breeders) the course is undoubtedly north and south through the islands, prac- 

 tically all the individuals going to breed on the islands north of the Pribilof group 

 and on the adjacent Alaskan and Siberian coasts, below and also beyond the Straits. 

 As to the course taken by the migratory flocks on their way south after reaching the 



• All Atlantic species are given, but there are a namber of additional Pacific forms confined to the 

 Asiatic sirde. The British Museum catalogue, vol. XXVI, gives a total of 26 species for this order, of 

 ■which 18 are Pacific, 5 are Atlantic, and 3 are common to both. 



5947_PT 3 24 



