Microhabitat use by breeding Southwestern Willow Flycatchers on the Gila River, New Mexico

The endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) breeds at numerous sites throughout its range that vary greatly in floristics, vegetation structure, and the extent of human alteration of the habitat. Here we present information on nesting habitat characteristics of Willow Flycatchers in the largest extant population of the subspecies along the upper Gila River in New Mexico. We compared 19 habitat variables between nest sites and sites not included in flycatcher territories. A logistic regression model identified three variables as significant predictors of flycatcher use: foliage density in the subcanopy, percent canopy cover, and number of boxelder (Acer negundo) stems. In mature riparian woodland, flycatchers displayed a significant preference for nesting in boxelder, and used two willow species less than expected by chance. Flycatchers in the Gila Valley tended to place nests rather high (mean = 7.6 m). The relative nest height, preference for dense foliage, and proximity to water were typical for the subspecies.