114 ANIMAL LIFE AND SOCIAL GROWTH 



is undisturbed tend to have negligible voices and 

 react to their fellows by sight, while those of the 

 nearby jungle, where vision is distinctly limited, 

 have remarkable vocal powers, with loud staccato 

 calls or insistent rhythms. With many animals, 

 including such widely separated forms as pigeons 

 and men, the social integration depends primarily 

 on the use of voice as a means of social control. 



In this connection, however, a note of caution 

 must be introduced. Animals may produce 

 sounds which are distinctly audible to man with- 

 out their having social or other importance to the 

 animal that produces them. Thus it has been 

 generally thought that the spring chorus of male 

 frogs helps orient wandering frogs and brings 

 them to a suitable breeding place. With some 

 frogs, careful stalking of "singing" individuals 

 through muddy swamps at night has been re- 

 warded by finding that female frogs were also 

 stalking the croaking male; in other cases there 

 seems to be no connection between the extensive 

 and far-carrying croaking of the frogs and migra- 

 tion to the breeding ponds. Such sounds appear 

 frequently to have only a generalized value in 

 that they stimulate the frogs to a pitch of excite- 

 ment which results in breeding activities rather 

 than directing migration to a given pond or of 

 directly benefiting an individual croaker. 



