112 ANIMAL LIFE IN DESERTS 



immediately under the bush, for they were without 

 a barricade of stones. One species of Wheatear 

 (Saxicola leucura) has a similar habit, nesting under a 

 rock and almost blocking the passage to the nest 

 with a mound of pebbles : the bird does this in the 

 Algerian Sahara, and also in the Sudan. Another 

 Wheatear {8, leucopyga cegra) shows what is probably 

 a development of the same habit, for it nests in holes 

 in rocks and crevices in walls and constructs a wide 

 path of flat stones up to the mouth of the crevice. 



Similar habits have been observed in other 

 countries, but no information is given as to the 

 direction of the prevalent wind, or the side of the 

 bush under which nests were habitually built. In 

 the Sudan Chapman has recorded the building of 

 barricades by an Ant-Chat (Oercomela scotocerca) 

 and a Lark {Ammomanes deserti), and states that 

 the Cercomela collects as many as 130 pebbles in 

 its barricade. This habit is the more remarkable 

 as it has been developed by birds which are not 

 closely related to one another ; one presumes that 

 it has originated independently in the Finch, in the 

 Wheatears and Ant-Chat which are closely related, 

 and at least once among the Larks. 



Of modifications of structure which are apparently 

 induced by the wind, the most striking is the 

 winglessness of many insects whose near relatives 

 in other types of country are winged. In the order 

 Orthoptera one may observe several series of insects 

 in which the wings are progressively reduced. Some 

 species have the wings so shortened that they are 

 useless for flight, but normal in structure and 



