18 THE HUMAN SHDE OF BHIDS 



as one might imagine, wingless and unable to place 

 their nests in trees or precipices ; they are remark- 

 able for their powers of flight, and might choose 

 any place they desire for their hcHnes. 



Many of these sand-dweDers seem quite unfitted 

 for their burrowing into the earth. The beautiful 

 capped petrel has become extinct because of its 

 burrowing habits. It was killed in its only breed- 

 ing-place, the islands of Guadaloupe and Dominica, 

 mainly because of the exposed position of its nests, 

 which made it the easy prey of blood-thirsty men 

 and animals. Yet strangely enough it must hare 

 believed itself safe in such a position. 



In the same way the sand martins and petrels 

 are to-day exposing themselves to the mercy of 

 the world by continuing to breed in exposed places. 

 It is not uncommon to see them cluster and flutter 

 against the sand-hills like a swarm of butterflies 

 trying to settle over a single flower in their effort 

 to secure the best site for their abnormal excava- 

 tions. 



Perhaps of all the cave-dweUers the sand mar- 

 tin, the smallest of the swallows, is ihe most human 

 in his methods of united work. Colonies of these 

 little feathered people combine and build regular 

 cities by binrowing into caves, or building UtOe 

 mud-houses one upon the other into a structure not 



