THE COLOURS OF DESERT ANIMALS 167 



black shadows, so long as they remain still ; un- 

 fortunately Wheatears are active, restless birds and 

 do not remain still for long. If we grant, what no 

 one who knows these birds in their haunts will 

 deny, that they are very easily seen, we may sup- 

 pose that they are protected from diurnal birds of 

 prey by their extreme wariness. This might aboUsh 

 the need for protective coloration, but does not in 

 the least explain the assumption of black, or black 

 and white colour. 



Remember, also, that the black, or black and 

 white Wheatears exist side by side with buff and 

 isabeUine congeners, and the nearly black race of 

 Calliptamus ccelesyriensis, so far as we know, never 

 replaces the normal buff typical race of its own 

 species. The buff and black exist side by side and 

 appear to fill identical places in the general economy 

 of nature. 



It is this recurrence of blackness, in widely 

 separated groups of animals, which is so remark- 

 able. If we may postulate that the Raven has 

 no predaceous enemies, that Eugaster (page 153) 

 is protected by its oily secretion from whatever 

 enemies it has, and that the Wheatears evade the 

 hawk by quickness and watchfulness, then we can 

 understand that desert-colour is not necessary to 

 these animals. But at once we are faced with their 

 imanimous choice of black : if they are freed from 

 the necessity of being buff, why are none of them 

 green, or red, or blue ? We must remember that 

 black absorbs more radiant heat than any other 

 colour. Presumably therefore a black creature must 



