370 



ELEMENTARY BIOLOGY 



FIG. 1 88. Finding a home for the young 



Nest of a bluebird in natural hollow of a tree 

 (From photograph by L. W. Brownell) 



With many animals the 

 boring or burrowing is re- 

 lated altogether to protec- 

 tion, as with animals that 

 bore into rocks (Fig. 186). 

 From our own point of 

 view the safety obtained 

 by an animal boring into 

 a rock would seem to be 

 purchased at the price of 

 liberty. But we may be 

 sure that from the pid- 

 dock's point of view this 

 trick of boring into the 

 rock causes no ill feeling. 

 There is safety, and there 

 is the possibility of getting 

 food as well, for the long 

 siphon projects into the 



FIG. 189. Prairie dogs 



These animals dig burrows underground and live in large colonies. (From 

 photograph by Elwin R. Sanborn) 



