Factors affecting nest survival of three species of migrant songbirds in the Greater Yellowstone Ecosystem
In the Greater Yellowstone Ecosystem (GYE), spatial patterns of habitat types and human land uses create an overlap between high-intensity human disturbance and productive habitat types at low elevations. This overlap suggests concern for species such as Neotropical Migrant songbirds, whose populations may depend on the productivity of individuals breeding in low-elevation habitats. We examined patterns of nest survival of three songbird species within the GYE to determine the relative importance of covariates of interest at nest-, patch-, and landscape-level spatial scales to nest survival. We hypothesized that covariates at several spatial scales would be important to nest survival and that broad-scale characteristics of the surrounding landscape would have the strongest spatial-level influence on nest survival. From 1997 to 1999 we located and monitored 233 nests of Dusky Flycatchers (Empidonax oberholserii), 129 nests of Warbling Vireos (Vireo gilvus), and 290 nests of Yellow Warblers (Dendroica petechia) in aspen and cottonwood habitats across southwestern Montana and adjoining portions of Idaho. We found that covariates at multiple spatial scales were important to the nest survival of all three species and that landscape-level variables had the strongest spatiallevel effects on the nest survival of Dusky Flycatchers and Yellow Warblers. For all three songbird species, higher substrates appeared to provide the most favorable nesting habitat and date and parasitism status were important variables in the model suites. Variation in the nest survival of Dusky Flycatchers was influenced by all spatial-level covariates, while the variation in nest survival of Yellow Warblers was influenced primarily by surrounding home density. Warbling Vireos appeared to be an edge species in the GYE, and their nest survival was influenced by smaller-scale covariates. Overall, our results emphasize variation in species' responses to surrounding habitat and land use features. We suggest that future studies should evaluate both a variety of species and a variety of habitat and land use features in order to determine how surrounding habitat and anthropogenic factors influence songbird communities.