364 



THE PUR SEALS OF THE PKIBILOF ISLANDS. 



Cireiimpolar (Molarctic) forms {IS species, S ireeding). 



Ga via arctica - Once. 



Stercorarius pomarinus Migrant. 



parasiticus Migrant. 



longicaudus Migrant. 



Pagophila alba Once. 



Sterna paradisaea Migrant. 



Xemaaabinii Migrant. 



Harelda hyemalia Breeds. 



Eniconetta stelleri Migrant. 



Crymophilus fulicarins Migrant. 



Phalaropus lobatus Breeds sparingly. 



Nyctea ny ctea Migrant. 



Aoanthis linaria Migrant. 



Of doubtful category. 



Anas boBchas subsp Probably Palaearctic. 



Histrionicus bistriouicus Probably Aleutican. 



Asio aocipitrinus subsp Probably Aleutican or Nearctio. 



The birds represented by the above three names have not been critically com- 

 pared. When this is done the Pribilof birds may be placed as indicated above. 



Exclusively American species form but an insignificant feature of the avifauna. 

 This is accounted for, in part, by the small area of the islands and consequent lack of 

 land birds, but principally because of the preponderating abundance of exclusively 

 Northern Paciiic forms ; in fact, the islands are located in the midst of a quite different 

 subregion, the Aleutican. More than half of the American or Nearctio forms are 

 casuals or accidental visitors. On the other hand, Asiatic forms have a much less 

 influence in numbers of species, but regarding individuals it is greater. Of the 6 

 species, 3 are noted for one specimen each, the other 3 being more or less numerous, 

 far more so than any American form. The circumpolar species need little comment. 

 The 29 Pacific forms, however, are entitled to some consideration. Of them, 16 may 

 be said to have close relatives on the Atlantic side of North America, but the remain- 

 ing 13 are utterly distinct, even 8 of them generically. If we add to these the various 

 members of the subfamily Phalerinae, which occur abundantly throughout the Aleu- 

 tian Islands, and several forms which as yet are unknown from the Pribilofs, we are 

 confronted with the fact that a very large number of Bering Sea birds have no close 

 natural affinity with Atlantic forms. Of the family Alcidae there are known from 

 the coasts of North America 25 species and subspecies, of which only 9 occur on the 

 Atlantic side. But a single species {Gepphus mandtii) occurs on both sides. Of the 12 

 genera in which these forms are placed, 3 — Alca, Plautus, and Alle — are exclusively 

 Atlantic. Three others — Fratercula, Uria, and Gepphus — have their species about 

 equally divided on each side. The remaining 6, belonging to the subfamily Phalerinae, 

 are exclusively Pacific. Besides these we have Lv/nda, Diomedea, Philacte, Heteractitis, 

 Apliriza, and Leucosticte, to say little of such forms as Rissa brevirostris, Oceanodroma 

 furcata, Sterna aleutica, and others, which have no representatives on the Atlantic 

 side. Most of the species and subspecies of the genera Fratercula, Uria, and Gep- 

 phus breed in the far north and are littte differentiated from each other. These birds 

 could readily have made their way from ocean to ocean during some extraordinarily 

 warm summer in the remote past, and having been unable to return have remained 

 and perpetuated their kind with consequent vaiiations. It would seem correct to 

 consider that the ancestral stocks of these genera were Pacific. 



Many eastern American species summer in western Alaskai, even to the shores of 

 Bering and the Arctic seas. Certain Siberian forms also summer in the same region. 

 On the American side there is now continuous land connection, but it may not always 



