| Predators can affect prey habitat use and behavior without direct interaction through the non-consumptive effects of predation, such as inducing fear. Fearful animals use vigilance, an anti-predator behavior, to reduce predation risk. However, there is a cost to vigilance. Time spent being vigilant for predators is time that is not spent foraging. This is known as the food-safety trade-off. This study used the predator-prey relationship between bald eagles (Haliaeetus leucocephalus) and ducks of the tribe Anatini in the Sacramento Valley of California to further explore the relationship between indirect predation and prey behavior. It is well documented that bald eagles feed on waterfowl. What is not known is the degree to which bald eagles indirectly affect waterfowl behavior and negatively impact fitness. This is especially important to understand as the Pacific Flyway waterfowl are threatened by habitat loss and climate change. I hypothesize that duck vigilance behavior is a function of perceived predation risk. As such, I predicted that as perceived bald eagle predation pressure increases, dabbling ducks would spend more time being vigilant, and less time on other behaviors, which may indicate a trade-off between avoiding predation and obtaining food. To test my hypothesis, time budgets of dabbling ducks at the Llano Seco Wildlife Refuge in the Sacramento Valley were collected and compared under varying levels of bald eagle predation pressure. Bald eagle surveys were conducted in the area around the study site and these time budgets were also analyzed over time as bald eagle numbers in the surrounding area fluctuated with fall and spring migrations. It was found that changes in the number of overwintering bald eagles in the area around Llano Seco between November and March did not influence duck vigilance behavior. However, as predicted, the sampled ducks did display more vigilance behavior when bald eagles were present at Llano Seco, compared to when they were not. Unexpectedly, duck vigilance behavior did not increase linearly with the number of bald eagles at the study site. Additionally, vigilance was greater when adult bald eagles were present, compared to when juveniles were present. Finally, the position of bald eagles in the environment (i.e., perching height and distance from the sampled ducks) had no effect on vigilance. The data did support the hypothesis that waterfowl behavior is a function of perceived predation risk, as evidenced by the increase in vigilance when bald eagles were present at the study site. However, this relationship did not hold up at a larger scale. The results lead to questions about how ducks detect potential threats, and how they respond. They also highlight the need to continue to monitor the relationship between bald eagles and waterfowl as we continue to face challenges associated with climate change. |