THE VERTEBRATE ANIMALS 



303 



Nesting Habits. Among the most interesting of all instincts 

 shown by birds are the habits of nest building. We have found 

 that some invertebrates, as spiders and ants, protect the eggs when 

 laid. In the vertebrate 

 group some fishes (as the 

 sunfish and stickleback) 

 make nests for the depo- 

 sit ion of the eggs. But 

 most fishes, and indeed 

 other vertebrates lower 

 than the birds, leave the 

 eggs to be hatched by the 

 heat of the sun. Birds in- 

 cubate their eggs, that is, 

 hatch them, by the heat of 



t . . IT TT Nest of a phccbe under the barn floor. 



their own bodies. Hence 



a nest, in which to rest, is needed. The ostrich is an exception; 

 it makes no nest, but the male and the female take turns 

 in sitting on the eggs. Such birds as are immune from the 

 attack of enemies because of their isolation or their protective 



coloration (as the puffins, 

 gulls, and terns), build a 

 rough nest among the rocks 

 or on the beach. The eggs, 

 especially those of the tern, 

 are marked and colored so 

 as to be almost indistin- 

 guishable from the rocks or 

 sand on which they rest. 

 Other birds have made the 

 nest a home and a place of 

 refuge as well as a place to 

 hatch the eggs. Such is the 

 nest of the woodpecker in 

 the hollow tree and the hang- 

 ing nest of the oriole. Some nests which might be easily seen be- 

 cause of their location are often rendered inconspicuous by the 

 builders ; for example, the lichen-covered nest of the humming birds. 



\'->t of the chimney swift. 



