COMPARATIVE STRUCTURE AND ORGANIZATION OF CANOPY BIRD ASSEMBLAGES IN HONDURAS AND BRAZIL

Birds of the forest canopy are an integral component of bird communities of neotropical forests but remain largely unstudied, inhibiting any broad characterization of their assemblages. We present the first description of a canopy-bird assemblage from Middle America and, on the basis of > 11000 detections in lowland rainforests in Honduras and Amazonian Brazil, compare two distant canopy-bird assemblages. The richness of canopy birds at the two sites was similar despite the much higher richness of forest birds in Brazil. Furthermore, abundance distributions differed significantly: in Honduras the assemblage was dominated by a small number of superabundant species and had fewer rare species, whereas in Brazil it had fewer abundant species and was thus more even. Omnivores and insectivores dominated the assemblages in terms of species richness, but omnivores were numerically more abundant. Species of forest edges and open habitats, sometimes considered an important component of forest-canopy avifauna, were underrepresented at both sites in comparison to null expectations drawn from the pool of species in each region. Long-distance migrants were more important in Honduras, where they constituted a third of canopy birds, yet species richness of migrants did not differ from a null expectation. Finally, we present a baseline classification of the core constituent species of bird assemblages in the canopy of lowland neotropical rainforests.