NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN 87 



bush-tanager than they would to the two sets of stimuli which would 

 be presented by the two species if they were not so similar to one 

 another. 



Black-cheeked warblers join and follow yellow-thighed finches more 

 frequently than they do individuals of any other species and relatively 

 more frequently than do brown-capped bush-tanagers. They may have 

 a definite special interspecific preference for yellow-thighed finches. 



Golden-crowned warblers were seen in the lower-altitude mixed 

 montane bush flocks slightly above 5,000 feet on the western slopes 

 of the Volcan de Chiriqui. They appeared to be rather strongly 

 gregarious among themselves (see also Eisenmann, 1957) and to play 

 an important nuclear role in some of the lower-altitude mixed flocks. 

 Their usual social role in such flocks may be similar to that of brown- 

 capped bush-tanagers in many higher-altitude mixed montane bush 

 flocks. 



YELLOW-THIGHED FINCH 



Social relationships between yellow-thighed finches and individuals 

 of many other species are extremely significant factors in the organi- 

 zation of most higher-altitude mixed montane bush flocks on the Vol- 

 can de Chiriqui. Yellow-thighed finches can play two different roles in 

 such flocks, and may play either one or both of these roles simultane- 

 ously and/or successively. They probably occur in the higher-altitude 

 mixed montane bush flocks of the Volcan de Chiriqui more frequently 

 than individuals of any other species, and they range farther up the 

 mountain than do brown-capped bush-tanagers. 



They tend to react actively to individuals of almost all the other 

 species they encounter. They usually join and follow individuals of 

 most other species much more frequently than they are joined and 

 followed by individuals of most other species. They do not, however, 

 perform joining and following reactions equally frequently. They 

 tend to follow individuals of most other species much more frequently 

 than they join individuals of the same other species. The actual num- 

 ber of joining reactions performed by yellow-thighed finches in most 

 higher-altitude mixed montane bush flocks is usually quite large, but 

 always, or almost always, much smaller than the number of following 

 reactions performed at more or less the same time. They certainly 

 follow individuals of other species without actually joining them much 

 more frequently than do any other members of any of the montane 

 bush alliances. 



