Thesis (M.S.)--Montana State University--Bozeman, 2005. / Title from PDF t.p. (viewed on June 10, 2006). Chairperson, Graduate Committee: Richard J. Aspinall. Includes bibliographical references (p. 93-105).

The southwestern willow flycatcher (Empidonax traillii extimus) is a federally-endangered neotropical migrant that breeds in the southwestern United States. The population of southwestern willow flycatchers on the South Fork Kern River in California was once thought to be one of the largest E. t. extimus populations. It declined from 38 pairs in 1997 to 12 pairs in 2000. My goals were to examine E. t. extimus habitat selection on the South Fork Kern River, to determine how habitat characteristics and food availability affect E. t. extimus demographics, and to make inferences about possible reasons for the decline. My first objective was to determine southwestern willow flycatcher habitat selection on the Kern on two spatial scales: territory and nest site. Southwestern willow flycathers selected habitat characteristics that appeared to be related to food availability, foraging ecology, or nest cover. Territories within the riparian forest were closer to water and the edge of forest and had fewer cottonwoods than unused areas. Nest sites had denser and more uniform canopy cover and a denser understory than randomly selected sites within territories. My second objective was to determine a relationship between measures of fitness (reproductive success and occupancy frequency) and territory categories (occupied 2 years, occupied 1 year, abandoned). Also, I examined the relationship between indirect measures of fitness, habitat characteristics and food availability, and territory categories. Compared to other territories, territories occupied more frequently had higher reproductive success, higher insect abundance indices, greater habitat heterogeneity, denser understories, and more stems 30-50 cm dbh. All of the habitat characteristics important in habitat selection and habitat quality on the South Fork Kern River were similar to other recent studies on E. t. extimus habitat selection and reproductive success. On the Kern, both suitable and optimal habitat appear to be limited and this limitation appears to be contributing to the population decline. Habitat quality may affect E. t. extimus demographics, particularly when the number of high quality territories in a population is limited as in site-dependent population regulation. Since the amount of suitable habitat is likely to continue to decline across the range of southwestern willow flycatchers, managers should consider manipulating habitat for high quality E. t. extimus habitat to aid conservation of this endangered species. / Master of Science

abstract: The Southwestern Willow Flycatcher (Empidonax traillii extimus) has been studied for over two decades and listed as endangered for most of that time. Though the flycatcher has been granted protected status since 1995, critical habitat designation for the flycatcher has not shared the same history. Critical habitat designation is essential for achieving the long-term goals defined in the flycatcher recovery plan where emphasis is on both the protection of this species and "the habitats supporting these flycatchers [that] must be protected from threats and loss" (U.S. Fish and Wildlife Service 2002). I used a long-term data set of habitat characteristics collected at three study areas along the Lower Colorado River to develop a method for quantifying habitat quality for flycatcher. The data set contained flycatcher nest observations (use) and habitat availability (random location) from 2003-2010 that I statistically analyzed for flycatcher selection preferences. Using both Pearson's Chi-square test and SPSS Principal Component Analysis (PCA) I determined that flycatchers were selecting 30 habitat traits significantly different among an initial list of 127 habitat characteristics. Using PCA, I calculated a weighted value of influence for each significant trait per study area and used those values to develop a habitat classification system to build predictive models for flycatcher habitat quality. I used ArcGIS® Model Builder to develop three habitat suitability models for each of the habitat types occurring in western riparian systems, native, mixed exotic and exotic dominated that are frequented by breeding flycatchers. I designed a fourth model, Topock Marsh, to test model accuracy on habitat quality for flycatchers using reserved accuracy assessment points of previous nest locations. The results of the fourth model accurately predicted a decline in habitat at Topock Marsh that was confirmed by SWCA survey reports released in 2011 and 2012 documenting a significant decline in flycatcher productivity in the Topock Marsh study area. / Dissertation/Thesis / M.S. Applied Biological Sciences 2013