Document: MAI-3-83-9

Response of avian assemblages to fragmentation in a tropical rain forest in Kenya.

MAINAGITOGO, G.* and W.M.JACKSON

University of Illinois at Chicago, Chicago Illinois 60607 USA ¹

Abstract:
Vegetation structure is well known to influence bird community organization. We assessed differences in forest bird assemblages and vegetation structure in six forest fragments in a tropical rain forest in Kenya. Two fragments were heavily disturbed, two were relatively undisturbed and two were of intermediate disturbance. We measured vegetation variables at seven distances from forest edge to interior. In all fragments, canopy vegetation cover, trees species richness, density and diameter increased along an edge-interior gradient, while vegetation structure (at 0-1 m height) decreased. Undisturbed fragments had a more complex vegetation structure than heavily disturbed fragments. We used mist-net and point-count surveys along the edge-interior gradient to sample bird assemblages, capturing 545 birds during 2100 net hours and detecting 626 individuals during point counts. Overall, we recorded a total of 53 bird species. Bird species richness and abundance was higher at the edge, although differences among forests were not entirely consistent for mist-net and point-count data. At the guild level, frugivores, arboreal granivores, and insectivores were more abundant at the edge than in the interior. At the species level, birds in the disturbed fragments were restricted to the forest interior whereas in the undisturbed fragments they were more widely distributed. Our results indicate that edge and interior bird assemblages are different. The difference in the distribution of birds among these habitats appeared to reflect constraints on habitat use imposed by vegetation structure, and could relate to differential distribution of food resources, especially fruits and insects.

Keywords: birds, forest fragmentation, Kenya

This abstract is being presented at: 2:45 PM in session:
Oral Session #14: Disturbance Effects on Bird Populations.