The effects of forest structure on occurrence and abundance of three owl species (Aves: Strigidae) in the Central Amazon forest

Abstract

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.

Spatial Variation in Bird Community Composition in Relation to Topographic Gradient and Forest Heterogeneity in a Central Amazonian Rainforest

“…The number of trees, fallen logs, snags, and canopy openness are variables known to affect individual birds species [7] or groups [38], yet they had little effect on the number of species or individuals (richness and abundance), and the species composition associated with our plots. One potential problem in assessing the effect of local environmental variables on birds is that, differently from herbs, palms, or frogs, most bird species hold relatively large territories for their size.…”

“…This study adds to the growing body of evidence suggesting that the natural heterogeneity found in a tropical forest can affect the local composition of animal and plant communities [17,21,[38][39][40][41][42][43][44][45][46][47][48]. Although we found that none of the variables analyzed were significantly associated with the number of bird species (richness) and individuals (abundance) recorded either on mist-nets or acoustic surveys, we found significant relationships between at least three parameters (elevation, distance to the nearest stream, and depth of the leaf litter) and bird species composition.…”

“…The depth of leaf litter on the forest ground can have several indirect effects on the avifauna, offering more substrate for small and large invertebrates for insectivorous birds, and even small vertebrates on which raptors (e.g., forest-falcons and owls) can prey [38]. Many bird species are known to actively search under dead leaves on the ground, such as leaftossers (Sclerurus) and foliage-gleaners (Automolus), and using leaf litter is a common practice in North America to attract birds to people's backyards.…”

“…Despite the good conditions of the RFAD's avifauna, which was last surveyed by us more than five years ago [7,32,38,48], careful monitoring is important, particularly given the continuous pressure created by the growth of the city of Manaus. Therefore, we recommend that long-term monitoring of bird communities using standardized methods be done at the RFAD [54] in order to ensure that processes of species loss (if unavoidable) are well documented.…”

Habitat selection by owls in a seasonal semi-deciduous forest in southern Brazil

“…Barros and Cintra (2009) indicated a high density of L. cristata and M. watsonii in points with this trait. The results of this paper indicated that the presence of hollow arboreal individuals had greater influence on the occurrence of S. virgata and G. brasilianum, who use these locations for nesting (Sick, 1997).…”