Abstract
We investigated how forest structure affects the occurrence and abundance of three owl species: the crested owl Lophostrix cristata Daudin, 1800, the Amazon pygmy owl Glaucidium hardyi Vielliard, 1990, and the tawny-bellied screech owl Megascops watsonii Cassin, 1849. We surveyed the owls mostly between 07:00 and 11:00 pm from July 2001 to April 2002, in eighteen 8 km transects along trails at the Ducke Reserve, Manaus, Central Amazon, Brazil. We staked out 50 x 50 m plots where the presence and absence of the owls were recorded. We compared some components of the forest structure between plots where owls were present and plots where they were absent. The spatial variation in these components were related to the occurrence and abundance of the owls using models of multiple logistic and multiple linear regressions analysis, respectively. Lophostrix cristata is rare in many other areas of the Amazon forest, but it was the most abundant in our study area. Lophostrix cristata and G. hardyi were more concentrated along the uplands (central plateau), which divide the reserve into two drainage water-basins. Megascops watsonii was distributed mainly in the southeastern part of the reserve. Glaucidium hardyi was more often found in areas with larger canopy openness. In areas with higher abundance of snags, there was significantly higher occurrence of L. cristata and M. watsonii. Megascops watsonii was also more abundant in areas with higher abundance of forest trees and in areas bearing shallower leaf litter on the forest floor. This study is the first to analyze at large spatial scale the effects of forest structure on neotropical forest top predator nocturnal birds. The results indicate that forest structure can affect the occurrence and abundance of owls in the Amazon forest.
Highlights
In the last four decades forest heterogeneity and habitat structure has been suggested to play a key role in structuring avian communities
It is very likely that changes in bird species richness and abundance in disturbed forests are mainly due to changes in some vegetation components, which could affect the availability of food resource and forest microclimatic conditions
We investigated how the forest environmental heterogeneity created by the variation in some forest structure components affect the occurrence and abundance of the following three owl species: the crested owl Lophostrix cristata Daudin, 1800, the Amazon pygmy owl Glaucidium hardyi Vielliard, 1990, and the tawny-bellied screech owl Megascops watsonii Cassin, 1849
Summary
In the last four decades forest heterogeneity and habitat structure has been suggested to play a key role in structuring avian communities Tropical forests, are a complex environment and detecting exactly what components of the vegetation affect bird distribution and abundance is not trivial. It is very likely that changes in bird species richness and abundance in disturbed forests are mainly due to changes in some vegetation components, which could affect the availability of food resource and forest microclimatic conditions Even primary forests show a relatively high degree of environmental heterogeneity. The role of this heterogeneity is mostly unexplored, but can affect the abundance and occurrence of birds and explain why there is such high bird diversity in a given area
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