Mixed flock composition and foraging behavior of insectivorous birds in industurbed and disturbed fragments of high-Andean **Polylepis** woodland
Faculty of Sciences. Biology
, p. 403-416
University of Antwerp
Mixed-species foraging flocks of birds are found in many forest communities, both in temperate and tropical forests. Such flocks are typically highly structured in terms of foraging behavior, with different species occupying different foraging niches with respect to foraging positions and/or techniques. In the Neotropics, most Studies have focused on species-rich flocks in lowland tropical forest, but little has been published on less diverse communities in montane Andean forests. We studied the composition and foraging behavior of birds in mixed insectivorous flocks in two small fragments of high-Andean Polylepis (Rosaceae) woodland near Cochabamba, Bolivia. One site represented largely undisturbed forest, while the other was more subject to anthropogenic influences clue to clearing, grazing and small-scale agriculture inside the remaining forest. Flocks were small in both areas (4-5 individuals per flock), but flock composition differed markedly between the two sites. In the undisturbed site, flocks were dominated by Polylepis habitat specialists, while non-specialists were numerically dominant in the disturbed site. Species were clearly separated by foraging mode and preferred foraging Substrate in the undisturbed site, but not so in the disturbed site. In the undisturbed site there was evidence for niche divergence between at least one pair of the main flocking species, while in the disturbed site some species tended to converge in foraging behavior when in each other's presence. It is concluded that both flock composition and flock structure in terms of niche separation differ markedly between the two sites, perhaps clue to the lower abundance of specialist species in the disturbed site.