Winter flocking of insectivorous birds in montane pine-oak forests in middle America

We studied mixed-species insectivorous bird flocks in pine-oak forests in M iddle America during three winter seasons to determine whether patterns of hock structure and dynamics were similar to those reported from other tropi cal sires. We also analyzed patterns of association among bird species, as well as their foraging behavior and the vegetation characteristics associat ed with birds in flocks. We encountered 333 flocks containing 144 species, of which 26 species had adequate sample sizes for analyses. The size and ra te of movement of the hocks were similar to those reported from other Neotr opical sires, however, the species richness of our flocks was lower than re ported in most other studies, perhaps due to simpler vegetation structure o r higher latitude. Only 3 of 50 significant correlations between species pa irs were negative, indicating that species generally were not restricted in their participation in mixed-species flocks by other species. In only one instance did we observe correspondence between the association of species-p airs in flocks and their foraging behavior. For most species there was no r elationship between association between species-pairs in flocks and vegetat ion parameters with which they were associated. Thus, additional factors be sides foraging facilitation and mutual association with particular vegetati on characteristics must be responsible for many of the positive correlation s among species pairs. We suggest that non-random association among species within flocks may result in part from enhanced vigilance for predator dete ction afforded by flock members using similar parts of the environment at t he same time.