Document Detail
Food abundance and habitat use of Varied thrushes near redwood forest edges
Abstract/OtherAbstract :
Thesis (M.S.)--Humboldt State University, Natural Resources: Wildlife, 2007, Previous research suggests that Varied thrushes (Ixoreus naevius) in redwood forests (Sequoia sempervirens) are sensitive to forest edges and are unlikely to breed in small forest fragments. Food abundance is likely to vary at the forest edge, and has been linked to habitat use and edge avoidance in some other forest-interior passerines, particularly other ground foraging insectivores. To determine the degree to which Varied thrushes avoid forest edges, and how this might be influenced by food abundance, I monitored third-order habitat selection of individual birds using radio telemetry, and sampled relative abundance of ground-dwelling invertebrates with pitfall traps across edge gradients in redwood forests of north coastal California. In addition, I measured vegetation structure and other habitat variables that may vary near forest edges and influence Varied thrush habitat use either directly or through effects on invertebrate distribution. I predicted that Varied thrush habitat use would be associated with invertebrate abundance, with both decreasing in proximity to forest edges, and increasing in proximity to streams. Of the 10 Varied thrushes monitored, only two used locations significantly farther from the edge than expected, and overall there was no clear pattern of edge avoidance or preference for streams in the birds studied. Invertebrate abundance was greater near forest edges, contrary to predictions, and was not affected by distance to streams or any of the habitat variables measured. Previous research indicating edge avoidance by Varied thrushes did not distinguish between second-order and third-order habitat selection. Since neither third-order edge avoidance nor edge effects on food abundance were apparent in this study, future research should focus on other potential edge effects at larger scales. The lack of evidence for edge effects also suggests that other mechanisms, such as conspecific attraction, may account for the absence of Varied thrushes from small redwood forest fragments., Natural Resources: Wildlife
Authors :
Brown, Gregory G.
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Contributors :
George, T. Luke
Publication Detail :
Publisher :  Humboldt State University     Type :  Thesis     Format :  11341154 bytes, application/pdf    
Date Detail :
2007-12-04, 2007-12-04, 2007-10
Subject :
redwood forest, varied thrush, edge effects
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Languages :  en_US    
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