UC Santa Cruz

Foraging behavior is a key ecological factor that has wide-ranging implications for individual fitness, and population and ecosystem dynamics. There are multiple hierarchical levels at which foraging behavior can be studied, from broad descriptions at the species level to the lowest level of within-individual variability. Intraspecific variation in foraging behavior is increasingly recognized as both widespread and ecologically important, and the occurrence and consistency of individual variation in foraging behavior has implications for the ability of populations to adapt to environmental change. The focus of my dissertation is on quantifying inter- and intra-individual variability in foraging behavior and the energetic implications of these differences for California sea lions (Zalophus californianus), an abundant generalist predator that inhabits a dynamic ecosystem. The fine- and broad-scale foraging behavior of adult female sea lions was quantified at multiple temporal scales using bio-logging technology and stable isotope analysis. Concurrent measurements of foraging behavior and energy expenditure were used to determine the energetic implications of behavioral variability. I found that female California sea lions used three foraging strategies: a shallow epipelagic strategy, a mixed epipelagic/benthic strategy, and a deep-diving strategy. This diversity in foraging behavior has likely allowed them to be successful in such a dynamic ecosystem, as I found evidence that female sea lions switched foraging strategies in response to changes prey availability. Despite this apparent flexibility, females generally exhibited behavioral consistency across both short and long time scales, including periods of reduced prey availability. Collectively, these results indicate that female California sea lions likely do switch foraging strategies, but it is unlikely that most sea lions routinely use all three strategies. Instead, they largely appear to play it safe by consistently using similar habitats and/or dive behaviors, which may be a successful strategy for managing uncertainty in environmental conditions. These individual behavioral differences have implications for survival and fitness, as fine-scale behavior affected the rate of energy expenditure. My dissertation highlights the importance of quantifying inter- and intra-individual variation in foraging behavior, particularly as it relates to understanding the strategies that individuals and species use to cope with limited prey resources in dynamic environments.