436 



EVOLUTION AND ANIMAL LIFE 



of other animals, are mere play, although singing primarily 

 belongs to the period of reproduction, and other calls and cries 

 result from social instincts or from the instinct to care for the 

 young. 



Climatic instincts are those which arise from the change of 



Fig. 270. — Nestlings of American bittern. P'our birds, of which two are shown in Fig. 

 269, two weeks old, at which age they showed marked fear of man. (Photograph 

 by E. N. Tabor, Meridian, N. Y., June 8, 1898. Permission of Macmillan Co., 

 pubUshers of "Bird Lore.") 



the seasons. When the wdnter comes the fur seal takes its 

 long swim to the southward; the "^dld geese range themselves 

 in wedge-shaped flocks and fly high and far, calling loudh^ as 

 they go; the bobolinks straggle away one at a time, flying 

 mostly in the night, and most of the smaller birds in cold 

 countries move away toward the tropics. All these movements 

 spring from the migratory instinct. Another climatic instinct 

 leads the bear to hide in a cave or hollow tree, where he sleeps 



