OF BRITISH BIltDS. 29 



Hiinantopus avocetta. 

 Ufjupa epops. 

 Platalea leucorodia. 



The range of the following five species does not extend quite so far 

 north, being only tropic and subtropic : — 



Hiinantopus Candidas. 

 Ardea purpurea. 

 Ardea garzetta. 

 Ardea alba. 

 Sterna hyhrida. 



West Pal.earctic Species. 



There are no fewer than 134 species of British Birds whose breeding- 

 range is confined to the western half of the Palsearctic Region. Of these, 

 10 do not extend eastwards beyond longitude 10°, 2 reach 25°, 19 are 

 found as far as 50°, and 4 as far as 60°, 45 breed as far east as 70°, the 

 range of 29 extends to 85°, and that of 25 to 110°, beyond which the East 

 Palsearctic Region is entered. 



Species whose Breeding-range extends from the Atlantic to 



Longitude 110°. 



There are twenty-five species of British Birds whose breeding-range 

 extends from the British Islands eastwards across Europe and West 

 Siberia, but does not extend (so far as is known) into East Siberia. The 

 West Palaearctic Region extends to the basin of the Yenesei about longitude 

 110°. Nature has fixed this boundary very exactly. The Himalayas 

 form a barrier which many migratory birds object to cross. The autumnal 

 stream of birds seeking milder winter- quarters divides, half the species 

 migrating westwards to winter in the basins of the Caspian and Mediter- 

 ranean seas if they do not wander as far as Africa, and the other half 

 migrating eastwards to winter in Japan, China, and the islands of the 

 Malay Archipelago if they do not wander as far as Australia. Birds 

 breeding in the valley of the Yenesei migrate westwards in autumn, whilst 

 those breeding in the valley of the Lena migrate eastwards. Of the 

 twenty-five species whose breeding-range extends to longitude 110°, that of 

 three may be regarded as arctic : — 



Ful/gula nigra. 

 Archibuteo lagopus. 

 Tringa niinuta. 



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