154 THE SOCIAL LIFE OF ANIMALS 



to find to what extent behavior is influenced by the 

 presence of others, and shall not consistently attempt 

 to assay possible values which may or may not be 

 involved. 



With many more or less social animals the group 

 up to a certain size facilitates various types of be- 

 havior. This is frequently called social facilitation. 



Shore Line 



Fig. 23. Manakin males establish rows of mating courts 

 in the Panamanian rain-forest. (From Chapman.) 



One phase of social facilitation is illustrated by some 

 observations of the mature student of birds, Frank E. 

 Chapman, (28) near the tropical laboratory on Barro 

 Colorado Island in the rain-forest of Panama. Mr. 

 Chapman found that males of Gould's manakin 

 establish lines of courting places (Figure 23). The 

 manakin is a small warbler-like bird, delicately 

 colored and relatively inconspicuous. Each of the 

 courting places is occupied by a single male; the line 

 thus formed extends for many yards through the 

 undergrowth of the rain-forest. From time to time 

 each day during the long nesting season, the males 

 resort to their individual cleared spots on the forest 



