Using GIS to guide field surveys for timberline sparrows in Northwestern Montana
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For many species, we lack the basic information on distribution and abundance that is needed for conservation and management. The timberline Brewer's sparrow (Spizella breweri taverneri), a migratory songbird previously known to breed only in the Canadian and Alaskan Rockies, was recently discovered in abundance in high-elevation areas of Glacier National Park, Montana, USA. Because the southern limit of this subspecies' breeding range was unknown, we developed a GIS-based model to predict timberline sparrow habitat along the Rocky Mountain front south of Glacier National Park. We field-tested the model by surveying 40 predicted sites in the Lewis and Clark National Forest. We found suitable habitat at 20 of the 40 sites (50%), and timberline sparrows were present at 4 of these; we also found timberline sparrows at one site that was not predicted. The discovery of nesting birds at Jones Creek, in the Teton River drainage, extends the known breeding range of this subspecies 50 km south. Our study indicates that, even with relatively few initial data, GIS can be successfully used as a tool to guide surveys for rare species. However, there are inherent limitations in models built with restricted data, and species' distributions can be driven by factors not readily modelled in a GIS. Therefore, GIS models often must be treated as working hypotheses, to be tested and improved as additional data become available.