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Associations of songbirds with their habitat in the Garry Oak (Quercus garryana) ecosystems of Victoria, British Columbia, Canada Feldman, Richard E.

Abstract

Urbanization fragments habitat, which affects bird abundance and distribution. This study tested the effect of urbanization on birds in fragments of Garry oak (Quercus garryana) and Douglas-fir (Pseudotsuga menziesii) ecosystems in Victoria, British Columbia. Birds were surveyed along transects in seven Garry oak patches in May and June of 2000. The patches were stratified by surrounding habitat type; four were surrounded by coniferous forest and three were surrounded by urban development. Birds were also surveyed in these adjacent habitats. Relative species abundance was determined using point counts along transects and territory mapping. Associations between bird abundances and urbanization in the landscape, patch size and Garry oak stem volume were tested. Linear regression models related environmental variables to the abundances of 17 common birds. The best model was chosen via Akaike's Information Criterion. For 42 birds, relationships between species composition, adjacent habitat type and vegetation composition were analyzed with detrended and canonical correspondence analysis and cluster analysis. For the 17 common species, 10 were strongly associated with the level of urbanization in the surrounding landscape. Seven species were associated with Garry oak stem volume, three positively and five negatively. Garry oak patches surrounded by urbanization had substantially different species assemblages than those surrounded by coniferous forest, in part due to the influence of coniferous trees in Garry oak patches. The results indicate that the level of urbanization in the broader landscape and tree composition in patches are significant factors associated with Garry oak bird assemblages. Conservation of Victoria's songbirds requires conserving and restoring a spectrum of habitats, from open savanna to closed-canopy coniferous forests. Management should be targeted at the landscape-scale and explicitly consider the extent of urbanization in the landscape.

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