NO. 7 FLOCKS OF NEOTROPICAL BIRDS MOYNIHAN 95 



species more often than they themselves are joined and followed ; and 

 they join and follow brown-capped bush-tanagers more often than 

 they do any other common species of the montane bush alliances. 



Although silver-throated tanagers are not very important members 

 of the mixed flocks on the Volcan de Chiriqui, they seem to be asso- 

 ciated with such flocks there more closely and more frequently, on the 

 average, than with mixed flocks on Cerro Campana (see below). 



(A few brief glimpses of a few speckled tanagers in the very hetero- 

 geneous lower-altitude mixed montane bush flocks on the Volcan de 

 Chiriqui would suggest that their role in such flocks is probably not 

 very different from that of silver-throated tanagers.) 



wilson's warbler 



This is another species that plays a very distinctive role in mixed 

 montane bush flocks. Wilson's warblers follow and join individuals 

 of other species much more frequently than they are followed and 

 joined. They also tend to follow individuals of other species more fre- 

 quently than they join individuals of other species. The relative fre- 

 quencies of interspecific following and joining reactions performed by 

 Wilson's warblers (at least when they are in shrubbery or low trees) 

 are very similar to the relative frequencies of interspecific following 

 and joining reactions performed by yellow-thighed finches ; but the 

 actual numbers of both types of reactions by Wilson's warblers are 

 usually much less than the actual numbers of the same reactions by 

 yellow-thighed finches in similar situations. Wilson's warblers also 

 come close to individuals of other species much less frequently than 

 do yellow-thighed finches. 



They tend to hang about the outskirts of a remarkably wide 

 variety of groups of other species in all the montane forest and 

 scrub habitats above 4,500 feet on the Volcan de Chiriqui (they may 

 also occur at lower altitudes, but I have not observed the birds of 

 lower altitudes). During the part of the year when Wilson's warblers 

 are in Panama, almost every large and medium-sized mixed mon- 

 tane bush flock (i.e., almost every flock composed of more than 

 two species) is accompanied by a single Wilson's warbler. Single 

 Wilson's warblers also attach themselves moderately frequently to 

 smaller mixed flocks and to single birds, pairs, family groups, and 

 larger unmixed flocks of almost every other species of all the mon- 

 tane bush alliances, as well as some species that usually remain apart 

 from the montane bush alliances. 



