OF BRITISH BIRDS 79 



Geographical Distribution of British Birds during- the 

 Breeding- Season outside the British Islands. 



The breeding range of the 391 species and subspecies of Birds 

 which undoubtedly have a claim to be regarded as British varies 

 very greatly both in the degrees of longitude which each species 

 covers during the breeding season and the climates which they 

 select for their breeding-grounds. 



The British Islands, being situated in the Palaearctic Eegion, 

 which extends eastwards across Europe and Siberia to Japan, 

 are naturally frequented by more species belonging to that 

 Region than by those belonging to any other Zoological Region. 

 About 28 per cent, breed across the Palsearctic Region from the 

 Atlantic to the Pacific, but are not known to breed in the Nearctic 

 Region. About 15 per cent, more breed across both these Regions. 

 The breeding range of another 15 per cent, may be described as 

 West Palgearctic, extending from the British Islands to Central 

 Asia, whilst that of an additional 11 per cent, extends some way 

 into Asia, but not as far as the Yenesei. The breeding range of 

 about 6 per cent, may be described as European, and that of about 

 3 per cent, as West European. About 5 per cent, may be regarded 

 as North Atlantic species, breeding on the coasts of West Europe 

 and East North America and on many of the intervening Atlantic 

 Islands. About 4 per cent, may be described as Circumtropical, 

 breeding on tropical islands. About 8 per cent, are wanderers 

 from the Nearctic Region which are not known to breed in any 

 part of the Palsearctic Region, whilst 2 per cent, are wanderers 

 from East Asia, 2 per cent, from Central Asia, and 1 per cent, 

 from East Europe. 



British Birds may be classified according to their breeding 

 ranges as follows : 



Circumpolar . ... . . .57 



Circumtropic . . . . . .12 



Nearly circumpolar ..... 4 



North Atlantic 20 



Nearctic 32 



Carried forward 125 



