366 THE FUK SEALS OF THE PEIBILOF ISLANDS. 



formerly numerous. The present rugged and precipitous coast line of the Pribilofs 

 and other islands of Bering Sea are certainly indicative of their former much greater 

 extent. Also the low coast line and the shallow seas of the western coasts of Alaska 

 point to the same previous condition. 



The relationships and zoogeographical distribution of the avifauna of the region 

 under consideration have often been variously determined by naturalists. Sometimes 

 considered as I^earctic, then as often Palaearctic, we now find them settled by 

 Professor Kewton as AlasJcan, a jjrovince of his Holarctic} On Dr. Merriam's pro- 

 visional maps of the principal life areas of North America, Alaska is divided between 

 his Arctic and Boreal, the last being distinguished as a region and described as 

 circumpolar.'^ I doubt if either of these names can be properly applied to primary 

 life divisions, for Palaearctic types must have been in existence long before glacial 

 times, which alone has produced Arctic and most of the present boreal conditions. 

 Besides, the avifauna of northern North America is not greatly different from, and 

 has most evidently been derived from, that of Eurasia. As well-known authorities 

 completely differ as to the values of the elements of the avifauna of Alaska, their 

 relations may be discussed here briefly as an effort toward determining the status of 

 the birds of the Pribilof Islands. 



We have first a very large number of forms, common transients of eastern North 

 America, which are summer residents of Alaska, and which reach that region by way 

 of the Mississippi and Missoari watersheds. Prom western North America also quite 

 a number of forms reach and enter Alaska as far as Kadiak Island and the Aliaska 

 Peninsula, though a few penetrate farther, even to Point Barrow. Certain forms 

 cross over from Siberia and also summer in Alaska. Others again, summering in 

 Alaska and Siberia, winter on the islands of the middle and southern Pacific. So 

 much for the true migrants. Eesident forms may also be divided into four groups 

 which are to be correlated with the same directions. We have resident forms in 

 northern Alaska whose nearest relatives are found eastward in British America. 

 Others are resident about Sitka and the Aliaska Peninsula and adjacent islands 

 whose nearest relatives are directly southward. The Siberian influence also has 

 stamped itself in such a wgy that we find resident Alaskan forms whose nearest 

 relatives are in Asia. Andidast, there is another group, resident about the shores 

 of Bering Sea and on the islands, and but rarely found elsewhere. The first 

 mentioned in each of these two divisions belong to the Nearctic subregion. Those of 

 the second belong to another division of the Nearctic, the Sitlcan. The third group 

 is essentially Palaearctic, and therefore Siberian, and the fourth Aleutican. 



Mixed as these bird elements certainly are, especially during the summer season, 

 we can, perhaps, readily unravel the causes which have produced such a conglomera- 

 tion. In preglacial times, when Arctic ice and its effects were absent, the continent of 

 North America was undoubtedly inhabited by species the great majority of which 

 were most evidently of Neotropical derivation. The archipelagic character of the 

 northern parts of North America and the land continuity of its southern portion 

 assisted in preventing any predominating influence from the Eurasian (Palaearctic) 

 continent. But with the gradual cooling incidental to preglacial conditions the Neo- 

 tropical influence gave way gradually to the hardier and nearer elements of Palaearctic 



I Diet. Birds, 1893, 331. = N. A. Fauna, No. 3, 1890, p. 24. 



