OF BRITISH BIRDS. 19 



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 o£ 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 Palsearctic Region, 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 Palsearctic, 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-ran o-es as 

 follows : — 



Circumpolar 57 



Circumtropic 12 



Nearly circumpolar 4 



North Atlantic 20 



Nearctic 32 



Palsearctic 110 



West Palsearctic : 



East to llO'' 25 



East to 85° 29 



East to 70° 45 



East to 60'' 4 



— 103 



Carried forward ........ 338 



