Effects of fine-scale and landscape-level habitat features on a sagebrush breeding birds of the southern Okanagan and Similkameen Valleys, British Columbia

I determined habitat associations for five species of songbirds breeding in sagebrush of the southern Okanagan and Similkameen Valleys, British Columbia. I examined the relative importance of scale for the presence and relative abundance of these species, through the measurement of vegetation floristics and structure at a local level (<100 m), and habitat context at three landscape scales (500 m, 1 km and 2 km). Vegetation and bird survey data were collected at 245 point count stations in 1998. Local-level habitat variables were derived from field surveys, while landscape-level variation was classified from a single Landsat Thematic Mapper ( TM ) image from 1996. Within sagebrush habitat the Landsat TM image was also classified at a fine-scale to determine if local-level habitat variation could be mapped by satellite data. Accuracy of the classification was assessed in 1999 by ground-truthing. Overall accuracy was 85%, and 78% for the sagebrush 'subtypes'. Local-level models from Landsat TM classified sagebrush habitat subtypes agreed with habitat associations identified from vegetation survey data, indicating that satellite data may be used as a surrogate for field data, although these associations were relatively weak. Performance of local, landscape, and local + landscape-level models was assessed from ranked Akaike's Information Criteria (AIC) scores. For all songbird species, logistic regression models showed the strongest habitat associations at a local level. Floristic variables were often more important than vegetation structure variables. Brewer's Sparrow was associated with large tufted perennials: parsnip-flowered buckwheat (Eriogonum heracleoides) and lupine (Lupinus sericeus or sulphureus). Lark Sparrow was positively associated with sand dropseed grass (Sporobolus cryptandrus), Vesper Sparrow (Pooecetes gramineus) was positively associated with lupines, and Western Meadowlark was positively associated with needle-and-thread grass (Stipa comatd). The addition of landscape-level variables usually improved the predictive ability of survey-derived local habitat association models. Habitat associations varied markedly for each species, and songbird relative abundance responded differently to the scale of measurements. Herb layer species identified as important in habitat associations were in turn correlated with rangeland management practices. Management recommendations are presented to direct conservation efforts in this highly threatened area.

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