160 ANIMAL LIFE IN DESERTS 



be at its highest. Instances such as this are few, 

 and the theory of protective or effacing coloration 

 which explains them well enough cannot be extended 

 generally. 



In the case of nocturnal beasts and birds of prey 

 it is still more difficult to explain colour as an effacer, 

 because even by moonlight colour hardly exists, and 

 differences between shades of colour are not appre- 

 ciated. All the same, there is a large group of desert- 

 coloured, nocturnal, predaceous forms, some hke the 

 owls hunting by sight, others Hke cats and jackals 

 and foxes by scent. All are pale in colour, and from 

 numerous examples, occurring in aU deserts, I choose 

 the following. Thomas has recently described a 

 Caracal from Asben in the South Central Sahara. It 

 differs from all known Caracals in its "exceptionally 

 pallid coloration and silvery ears." It is "a desert- 

 coloured form with whitish ear-pencils." Among 

 the birds the Eagle Owl (Bubo bubo) is a wide-ranging 

 species able to support itself equally in the forests of 

 Scandinavia and the steppes and deserts of Persia, 

 Transcaspia and Egypt. A large number of sub- 

 species have been described and they form a most 

 interesting gradation from the large dark forest 

 birds of Europe and North- West Asia to such small 

 and pale desert forms as Bubo b, aharonii in Southern 

 Palestine ; B. b. ascalaphus in North Africa and 

 Egypt ; B. b. turhomanus in Transcaspia, East 

 Persia and Turkestan, and other forms. 



There is, of course, a stiU larger group of animab 

 which are preyed upon and which are nocturnal. 

 Nearly aU the Jerboas and Gerbils of the Old World, 



