3G4 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



Circi(7npolar {Holarctic) forms (13 species, 2 breeding). 



Gavia arctica Once. 



Stercorarius pomarinus Mijjiant. 



parasiticus Migrant. 



longicandus Migrant. 



Pagopbila alba Once. 



Sterna paradisaea Min-raut. 



Xema sabinii Miwrant. 



Harebla hyemalis Breeds. 



Eniconetta stclleri Migrant. 



Cryuiophilus i'ulicarius Migrant. 



Pbalaropus lobatiis Breeds sparingly. 



Nyctea iiyctca Migrant. 



Acanthis linaria Migrant. 



Of douhifiil category. 



Anas boschas subsp Probably ralaearctic. 



Histriouicns li istrionicus Probably Ahuticaii. 



A.sio accipitrinns subsp Probably Aleutican or XcarcHc. 



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

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



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

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

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

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

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

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

 influence in numbers of species, but regarding individuals it is greater. (3f 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, IG may 

 be .said to have clo.se 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 Phalcrinac, 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 AkUJac there are known from 

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

 Atlantic side. Hut a single species ( Cepphns mawUii) occurs on both sides. Of the 12 

 genera in which these forms are placed, 3—A1ca, Flautus, and AUe—are exclusively 

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

 equally divided on each side. The renmining G, belonging to the subfamily Phalerhiae, 

 are exclusively Pacific. Besides these we have Lunda, Diomedea, PhUacte, JleteractitiJ, 

 Aphriza, and Leucosticte, to say little of such forms as Eissa brevirostris, Oceanodroma 

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

 side. Most of the si)ecies and subspecies of the genera Fratercula, Uria, and Cep- 

 phm breed in the far north and are little dittereutiated from each other. These birds 

 could readily have made their way from ocean to ocean*(luring .some extraordinarily 

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

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

 consider that the ancestral stocks of these genera were Pacific. 



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

 Bering and the Arctic seas. Certain Sibermn forms also summer iu the same region. 

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



