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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



in Britain; but the number of breeding passerines is less than one- 

 eighth of the British. In part this is due to the unfriendly climate 

 and the barrenness of much of the island. Although Iceland barely 

 touches the Arctic Circle, real trees cannot grow except in two small 

 sheltered localities, and both vegetation and insect life have much less 

 luxuriance and variety than with us in Britain, while the winter, of 

 course, is such that very few species of bird could possibly live 

 through it. 



In Spitsbergen, farther poleward, we find a marked further drop, 

 both in the total and the passerine percentage- The best way to 

 bring this home is by means of a table : 



TABLE 1. — Breeding species of hirds in Britain, Iceland, and Spitsbergen 



There is, however, also the fact that Iceland is an island, and a 

 fairly remote one, lying over 500 miles from the Hebrides (a little 

 more from Cape Wrath, the nearest point of the British mainland), 

 and close on 300 miles from Faeroe. Admittedly the distance north- 

 westward to the Greenland coast is under 200 miles; but Greenland, 

 especially in these latitudes, is so forbidding that very few species 

 can have used it as a stepping-stone to Iceland. 



Now remote islands invariably show a fauna and flora which is 

 impoverished compared to that of the nearest mainland. This is 

 usually set down to the difficulties presented to birds by a long sea 

 passage, especially to small terrestrial species or those with feeble 

 flight. In addition, an island is likely to have fewer kinds of habi- 

 tats than a mainland area, and this may cut down the number of 

 species which can find a permanent niche in its biological economy, 

 even if they manage to reach it. 



It is of course difficult to say just what birds are lacking merely 

 because they have failed to overcome the sea barrier. Some ap- 

 parent candidates turn out, on reflection, to be ruled out for other 

 reasons. Thus the fact that among the thrushes the redwing breeds 

 in Iceland and the fieldfare does not is not so surprising when we 

 remember how the fieldfare seems much more definitely wedded to 



