Does Habitat Matter in an Urbanized Landscape? The Birds of the Garry Oak (Quercus garryana) Ecosystem of Southeastern Vancouver Island

Garry oak (Quercus garryana) was once a dominant habitat type on southeastern Vancouver Island, British Columbia but urbanization has severely fragmented and reduced its occurrence. This study tests whether bird abundance in remnant patches of Garry oak and adjacent Douglas-fir (Pseudotsuga menziesii) is related to Garry oak volume, patch size or urbanization. Breeding bird populations were surveyed at seven Garry oak sites and four adjacent Douglas-fir sites. Relationships between environmental variables and abundance of 17 species of birds were inferred by selecting the best linear regression model by Akaike Information Criterion. For five species, the best model included Garry oak volume, two species being positively related to oak habitat and three species preferring Douglas-fir habitat. Eight species were associated more with patch size or level of urbanization in the surrounding landscape. For these species, the effects of fragmentation overwhelmed the importance of habitat differences. While habitat degradation of remnant patches is a conservation issue, the bird community of this urbanizing landscape would most benefit if human modification of the surrounding landscape was reduced.