166 ANIMAL LIFE 



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

 first was being shared by all. The well-known association 

 of pelicans in fishing is a good example of the advantage of 

 a gregarious and mutually helpful habit. The pelicans 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 (Fig. 101) live to- 

 gether in small bands, posting sentinels whenever they 

 are feeding or resting, who watch for and give warning 

 of the approach of enemies. The beavers furnish a well- 

 known and very interesting example of mutual help, and 

 they exhibit a truly communal life, although a simple 

 one. They live in " villages " 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 communi- 

 ties 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 grega- 

 rious, 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. 



