Chap. 6 



MUTUAL RELATIONSHIPS OF ANIMALS 



101 



•t" 



•^ 



Fig. 6.8. Hundreds of white pelicans rising and thousands still to rise from a 

 preserve on Lake Washington, State of Washington. A typical aggregation of ani- 

 mals associated because something in the environment has beckoned them. (Photo- 

 graph by Hugh M. Halliday. Courtesy, National Audubon Society.) 



ment drives or beckons: the cold of winter, the heat of summer, the dark that 

 starts the crows crowding into their roosts, the low tide that leaves new forage 

 for the gulls, the lakes kept as safe stopping places for migrating waterfowl 

 (Fig. 6.8). Animals are brought together by accident; starfishes, snails, and 

 others thrown on the beach enmeshed in seaweed. The spring gatherings of 

 frogs and toads and the shoals of spawning fish are aggregations stimulated by 

 climatic conditions and breeding habits. 



Social Organization of Animals. Among invertebrates social organization 



