Date of Award:
Master of Science (MS)
The last stronghold of the California Willow Flycatcher (Empidonax traillii) population, which exists in the Sierra Nevada, continues to decline, necessitating a clearer understanding of how meadows provide habitat for the species. To gain this understanding, we assessed vegetation type, saturation levels, and invertebrate species at 51 different sites within four meadows located in the Little Truckee River drainage. 17 of these sites were occupied by nesting Willow Flycatcher during the time of the study, 17 sites had been occupied by nesting Willow Flycatcher in annual surveys between 1997 and 2010 but are no longer used, and 17 sites had never been used by nesting Willow Flycatcher. We found that occupied sites were generally far wetter than unused sites. Total saturation varied from 88% to 100% and total inundation varied from 20% to 52%. Sedge vegetation coverage was also much higher in occupied sites than unused sites and varied from 62% to 90%. Abandoned sites were found to not be suitable for breeding Willow Flycatcher because they were either too dry (low food abundance) or they were too wet (decreased shrub quality). Food items desired by Willow Flycatcher were found to be higher in abundance within wetter occupied sites compared to drier unused sites. In addition to evaluating vegetation coverage, saturation levels, and invertebrates, we examined Willow Flycatcher diet, foraging behavior, and food/habitat relationships by using video footage of nestlings being fed and field observations. Over 75% of the Willow Flycatcher diet was represented by Lepidoptera (moth caterpillar), Raphidioptera (snakefly), Ephemeroptera (mayfly), Odonata (dragonfly and damselfly), and Hemiptera (leafhopper). Aquatic invertebrate food items composed 42% of the diet and aquatic habitat features such as stream channels and oxbow ponds were found to be important. Overall, gleaning and hawking foraging methods were used relatively equally, 49% and 51% of the time, respectively. Foraging often took place outside of territory boundaries and some food items, such as Raphidioptera, were caught outside of meadow boundaries. Diets and foraging behavior also varied throughout the day with some food items, such as Ephemeroptera and Lepidoptera, being targeted only during certain times of the day.
Dietrich, Scott E., "Habitat, Diet, and Foraging Ecology of Willow Flycatcher in Sierra Nevada Meadows" (2020). All Graduate Theses and Dissertations. 7950.
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