ANIMAL COMMUNITIES AND SOCIAL LIFE 331 



about the dead body of a horse. The food found by the 

 first was being shared by all. The association of pelicans in 

 fishing is a good example of the advantage of a gregarious 

 and mutually helpful habit. The pelicans sometimes go 

 fishing in great bands, and, after having chosen an appro- 

 priate place near the shore, they form a wide half-circle 

 facing the shore, and narrow it by paddling toward the 

 land, catching the fish which they inclose in the ever-nar- 

 rowing circle. 



The wary Eocky Mountain sheep live together in small 

 bands, posting sentinels whenever they are feeding or rest- 

 ing, who watch for and give warning of the approach of 

 enemies. The beavers furnish a well-known and very inter- 

 esting example of mutual help, and they exhibit a truly 

 communal life, although a simple one. They live in " vil- 

 lages " or communities, all helping to build the dam across 

 the stream, which is necessary to form the broad marsh 

 or pool in which the nests or houses are built. Prairie- 

 dogs live in great villages or communities which spread 

 over many acres. They tell each other by shrill cries 

 of the approach of enemies, and they seem to visit each 

 other and to enjoy each other's society a great deal, 

 although that they afford each other much actual active 

 help is not apparent. Birds in migration are gregarious, 

 although at other times they may live comparatively alone. 

 In their long flights they keep together, often with definite 

 leaders who seem to discover and decide on the course 

 of flight for the whole great flock. The wedge-shaped 

 flocks of wild geese flying high and uttering their sharp, 

 metallic call in their southward migrations are well known 

 in many parts of the United States. Indeed, the more 

 one studies the habits of animals the more examples of 

 social life and mutual help will be found. Probably most 

 animals are in some degree gregarious in habit, and in all 

 cases of gregariousness there is probably some degree of 

 mutual aid, 



