MUTUAL AID AND COMMUNAL LIFE AMUXCi ANIMALS 3S1 



wolves which hunted the buffalo show the advimta^'e of nuitual 

 help in aggression as well as in protection. In this ])an{hng 

 together of wolves there is active cooperation among indivichials 

 to obtain a common food sui)i)ly. What one wolf cannot do— 

 oliat is, tear down a buffalo from the edge of the herd — a dozen 

 can do, and all arc gainers l)y tlie operation. 



On tlie other hand, the vast assembhng of sea birds 

 on certain ocean islands and rocks is a conchtion i)robal)ly 

 brought about rather by the si)ecial suitableness of a few phices 

 for safe breeding than from any sjXM-ial nuitual aid afforded; 

 still, these sea birds und()ul)te(lly coml)ine to drive off attack- 

 ing eagles and hawks. Eagles are usually considered to Ije 

 strictly solitary in habit (the imit of solitariness being a ])air, 

 not an individual) ; but the description, by a Russian naturalist, 

 of the hunting habits of the great wliite-tailed eagle (Ilali- 

 a'etos alhicilla) on the Russian stei)i)es shows that this kind of 

 eagle at least has adopted a gregarious habit, in which mutual 

 help is plainly obvious. This naturalist once saw an eagle 

 high in the air, circhng slowly and widely in perfect silence. 

 Suddenlv the eagle screamed loudlv. "Its crv was soon an- 

 swered by another eagle, which approached it, and was followed 

 by a third, a fourth, and so on, till nine or ten eagles came to- 

 gether and soon disappeared." The naturalist, following them, 

 soon discovered them gathered 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 examj^le of the ad- 

 vantage of a gregarious and mutually hel})ful habit. The 

 peHcans sometimes go fishing in great bands, and, after having 

 chosen an appropriate place near the shore, they form a wide 

 half-circle facing the shore, and narrow it by j^addling toward 

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

 narrowing circle. 



The wary Rocky Mountain sheep (Fig. 234) live together 

 in small bands, posting sentinels whenever they are feeding or 

 resting, who watch for and give warning of the a]iproach of 

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

 ing example of mutual help, and they exhibit a truly com- 

 munal life, although a simple one. They live in "villages" 

 or communities, all hel]Mng 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 



