Scale perspectives in habitat selection and animal performance for Willow Flycatchers (Empidonax traillii) in the central Sierra Nevada, California
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Habitat selection is often evaluated using a hierarchy of spatial scales, from coarse selection of general vegetation communities to fine selection of specific foraging or nesting locations. Rarely, however, are these differing scales examined to determine how they relate to habitat quality (as measured by animal performance). We examined how habitat selection at each of three scales (meadow, territory, and nest) constrained or influenced selection at other scales, and then assessed how these selections related to animal abundance, territory productivity, and nest success for Willow Flycatchers (Empidonax traillii) in the Sierra Nevada, California. During 1997 and 1998, we surveyed and monitored 104 meadows to document Willow Flycatcher abundance, territory, and nesting status. Vegetative and hydrologic variables were measured in association with all meadows, territories, and nest sites. We used multiple linear and logistic regression to determine which variables best predicted animal performance at each of the three spatial scales, and we used logistic regression to compare nest sites, territories, and occupied meadows with unused or adjacent areas at each scale. The patterns of selection were relatively consistent across scales, with riparian shrub cover a primary predictor of habitat selection for meadows, territories, and nest sites. At successively finer scales, Willow Flycatchers selected areas with higher riparian shrub cover. Increased shrub cover also predicted both Willow Flycatcher abundance and territory success, suggesting that the habitat characteristics selected by these birds also conferred high animal performance and thus habitat quality.
