Behavioral Responses of Willow Flycatchers, \u3ci\u3eEmpidonax traillii\u3c/i\u3e, to a Heterogeneous Environment

Spatial heterogeneity impacts population and community-level dynamics including species-level dispersal patterns, the use and availability of refugia, predator/prey dynamics, and reproductive fitness. Understanding how wild animal populations respond to environmental heterogeneity is essential for their proper management and conservation. In this study, I examine the responses of Willow Flycatchers to spatial heterogeneity in the distribution of their food and habitat resources. Over the course of three breeding seasons, I radio- tracked Willow Flycatchers at Fish Creek in Manti-La Sal National Forest in Utah, recorded detailed behavior data at each radio location, and collected fecal, feather and insect samples. I formulated individual and population-level Bayesian spatial resource selection functions to model Willow Flycatcher foraging and vocalization behavior on multiple scales. These models indicate that vocalization and foraging behavior are spatially segregated within the home ranges of Willow Flycatchers. Further, Willow Flycatchers were found to use mature riparian habitat for vocalizing while they used a variety of habitat types for foraging. The insect samples were used to identify distinct carbon and nitrogen stable isotope signatures for the aquatic and terrestrial insect communities at Fish Creek. In conjunction with the fecal samples, I used the stable isotope signatures to determine the contribution of aquatic versus terrestrial insects to the Willow Flycatcher diet. Aquatic insects comprised a larger proportion of the diet of adult than nestling Willow Flycatchers. This suggests that adult flycatchers consume a diet that is distinct from the one they feed to their nestlings. Finally, I compared space use characteristics in two populations of Willow Flycatchers: a population of the endangered Southwestern Willow Flycatcher at Roosevelt Lake, Arizona and another belonging to a non-endangered subspecies of Willow Flycatcher at Fish Creek, Utah. Differences in space use were found largely among breeding flycatchers while space use characteristics in non-breeding Willow Flycatchers did not differ across populations. This suggests that space use patterns in non-breeding Southwestern Willow Flycatchers may be generalizable to non-breeding flycatchers from non-endangered populations. This study expands our understanding of how Willow Flycatchers respond to spatial heterogeneity while its key findings have management and conservation implications for the species