UC Davis

In this dissertation, I investigate the roles that aquatically derived resources play in the community structure and foraging behavior of wild birds in high-elevation regions of the Sierra Nevada mountains of California. Wilderness designations protect ecologically important areas from intense human development, which is critical to conserving them but also poses a challenge in accessibility to studying them. To address the need for data-rich methodology in wilderness, I piloted the use of passive acoustic monitoring (PAM) to collect data on the community composition and activity of birds breeding in alpine areas in 6 headwater basins throughout Sequoia and Kings Canyon National Parks (SEKI). In my first chapter, I investigated the potential for acoustic indices—mathematical measurements of variation in acoustic activity—to be used as proxies for avian diversity within three large acoustic datasets from U.S. National Parks that differ in spatial breadth and gamma diversity. Using a Random Forest with several widely used acoustic indices to predict observed species richness in 5,670 minutes of audio recording, I found that acoustic indices predict coarse but not fine differences in species richness. I discuss opportunities and limits in the application of acoustic indices as reliable measures of avian diversity in research and management contexts. Trout introductions to historically fishless high-elevation lakes cause trophic cascades within the aquatic system, resulting in simplified, species-poor food webs and major reductions in aquatic insect emergences. In the Sierra Nevada, over half of all historically fishless lakes now contain self-sustaining populations of trout, but the effects of this landscape-level disturbance on the surrounding terrestrial food web are largely unknown. In my second chapter, I investigated whether introduced trout impact the adjacent avian community via a reduction in aquatic insect emergences, a potentially valuable food source for birds. While avian alpha diversity (species richness) did not differ between lake types, I documented significant turnover in community composition, with fish-containing and fishless lakes diverging in the relative abundances of several alpine bird species common in the regional species pool. Differences in overall avian abundance between lake types approached statistical significance but were subtle: estimated avian abundance at fishless lakes was higher by roughly 1 individual per 300m sampling radius. Preliminary analysis of a Before-After, Control-Impact experiment involving fish removal at a study lake revealed a significant twofold increase in overall bird abundance following trout removal. The magnitude of this increase in bird abundance may be indicative of a response to a short-term increase in aquatic primary production but may also suggest that currently fish-containing lakes would be capable of hosting a greater abundance of birds in the absence of trout. The third chapter investigates how seasonality shapes the role of aquatic resources in the diets of breeding mountain white-crowned sparrows (MWCS). I used stable isotope analysis of carbon and nitrogen to quantify both trophic position and origin (aquatic or terrestrial) of the diets of nestling MWCS. Both trophic position and the proportion of food of aquatic origin of nestling diet changed directionally over the course of the season, with late-hatching nestlings being provisioned a diet both lower in trophic position and in aquatically derived prey than early-season nestlings. I discuss the nutritional benefits of aquatic prey items to consumers and how both seasonality and resource availability may impact both adult provisioning behavior and nestling quality. As global climate change accelerates warming and drying, especially in the alpine and at high latitudes, I argue that understanding the dynamic connections between the aquatic and terrestrial food webs is necessary to identifying, managing, and conserving climate refugia in these areas. Through observational and experimental field study at both the landscape and individual scales, I elucidate previously undocumented links between aquatic and terrestrial systems, demonstrate how the introduction of fishes to high-elevation waterways disrupts those linkages, and provide information about methodologies that can aid in efficient, data-rich, and minimally invasive research in critically important and imperiled wilderness areas.