NO. 7 FLOCKS OF NEOTROPICAL BIRDS — MOYNIHAN IOO, 



they are comparatively simple and their organization may reveal 

 something of the probable course of evolution of mixed flocks in 

 general. 



MIXED FLOCKS OF SMALL FINCHES 



Several species of small finches tend to associate with one another 

 more or less frequently in various lowland areas in Panama. Among 

 these species are the variable seedeater, the yellow-bellied seedeater, 

 the thick-billed seed-finch {Oryzoborus funereus), the blue-black 

 grassquit (Volatinia jacarina), and the dark-backed goldfinch (Spinus 

 psaltria) . 



The mixed flocks of small finches in Panama never include as 

 many species as the larger mixed blue and green tanager and honey- 

 creeper flocks or mixed montane bush flocks ; but they do seem to be 

 specialized societies, not merely casual aggregations. Some aspects 

 of the social relationships between some of these finches have already 

 been discussed elsewhere (Moynihan, i960). The most interesting 

 feature of many mixed flocks of small finches is the physical resem- 

 blance between some of the species included in the flocks. The adult 

 males of several of these species of finches, including species that do 

 not seem to be very closely related to one another, have largely or 

 completely black plumage. This may be "social mimicry." It is pos- 

 sible that one or more of these species have evolved such plumage 

 simply to facilitate associations with other species having similar 

 plumage. 



A few additional features of the mixed flocks of small finches 

 would suggest that their organization is most nearly similar to that 

 of the mixed blue and green tanager and honeycreeper flocks. The 

 finches that occur together most frequently in the lowlands of central 

 Panama near the Canal Zone are the variable seedeater and the blue- 

 black grassquit. Relatively brief observations of mixed flocks com- 

 posed of these two species alone would suggest that the usual social 

 roles of both species in such flocks are very clear cut and one sided. 

 Blue-black grassquits join variable seedeater s very frequently, but 

 variable seedeaters seldom or never join blue-black grassquits in such 

 flocks. (The usual social role of variable seedeaters in mixed flocks 

 that include individuals of some other species, such as yellow-bellied 

 seedeaters, may be rather different, at least in some respects ; but I 

 have not been able to measure the extent of this difference.) The 

 contrasting reactions of variable seedeaters and blue-black grassquits 

 in mixed flocks that do not include other species seem to be correlated 



