OF BRITISH BIRDS. 



39 



great extremes for their young. Hence, though we find an epitome of 

 Arctic ornithology on the tundras of tlie Dovre Fjeld, we look in vain for 

 a similar epitome on the higher Alps. Though the mean temperature 

 during July may he the same^ the cold nights produce a climate sufficiently 

 different to prevent most Arctic Birds from using it as a breeding-ground. 

 It cannot be too clearly laid down that the latitudinal distribution of 

 Birds is purely climatic. 



The division of the summer climate of the w^orld into three zones — Arctic, 

 Temperate, and Tropic — is scarcely narrow enough for the present purpose, 

 and it will be more convenient to restrict somewhat the limits of the Arctic 

 and Tropic zones, and split the Temperate zone in two parts, which might 

 be called Subarctic and Subtropic respectively. 



The mean temperature for July would then range as follows in each of 

 the four climates : — 



Arctic from 40° to 53°, including Iceland, the Highlands of Scotland, 

 North Scandinavia, the Dovre Fjeld, the tundras of East Russia and 

 Siberia, and the mountains of East Siberia. 



Subarctic from 53° to 65°, including the British Islands, Central Europe, 

 South Siberia, and the north island of Japan. 



Subtropic from 65° to 77°, including South Europe, tlic mountains of 

 North Africa, Asia Minor, Central Asia, North China, and the south 

 island of Japan. 



Tropic from 77° to 90°, including the plains of North Africa, Arabia, 

 India, South China, and the Malay Archipelago. 



The climatic breeding-range of British Birds may be summarized as 

 follows : — 



Arctic 78 



Arctic and subarctic 57 



Arctic, subarctic, and subtropic ... 5 



Subarctic 64 



Subarctic and subtropic 116 



Subarctic, subtropic, and tropic ... 21 



Subtropic 28 



Subtropic and tropic 11 



Tropic 11 



391 



