166 ANIMAL LIFE 
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 Rocky 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. 
