OF BHITISH BIRDS 99 



three choose a subtropic climate 



Charadrius asiaticus, 

 Larus ichthyaetus, 

 Otis macqueeni ; 



one may be regarded as subtropic and tropic 

 Caprimulgus cegyptius. 



The breeding range of one species extends from the valley 

 of the Elbe to that of the Yenesei and may be regarded as sub- 

 arctic and subtropic 



Corvus corone cornix. 



The breeding range of four species extends from South-East 

 Russia to some part of Central Asia 



Saxicola isdbellina. 

 Alauda sibirica. 

 Vanellus gregarivs. 

 Pastor roseus. 



They are all accidental visitors, breeding in a subtropic climate. 



Climatic Distribution of British Birds during the 

 Breeding Season. 



Very few birds have a very wide climatic distribution during 

 the breeding season. They pay little or no attention to parallels 

 of latitude, but they appear to be very particular to choose 

 breeding-grounds with a mean temperature during the breeding 

 season to suit their individual requirements. The isothermal lines 

 of July may be regarded as forming natural boundaries of the 

 latitudinal range of most of our birds during the breeding season, 

 if due importance be attached to two factors which play a very 

 important part in modifying it. In our maps the isothermal lines 

 are corrected to sea-level. The corrections must of course be 

 entirely disregarded in considering the breeding ranges of birds, 

 which are governed by the actual mean temperature, irrespective 

 of cause. The climate may be produced by a low elevation at a 



