UC Santa Cruz

Recent declines in Arctic sea ice have been linked to reductions in body condition, survival, and population size of polar bears (Ursus maritimus) in some regions of the Arctic. Reduced foraging opportunity is hypothesized as the primary mechanism of sea-ice linked declines, but increased energy expenditure, as a result of changing sea ice composition and extent may be an additional underlying mechanistic factor. Field metabolic rates of polar bears have been previously unknown and limited information has existed on foraging or other behaviors in polar bears while on the sea ice. Such data are increasingly needed to better understand polar bear habitat use and improve projections of the effects of climate change on global polar bear populations. The primary objectives of this work were to: 1) develop metrics to remotely quantify wild polar bear foraging rates and behaviors; 2) measure the energetic costs of resting, walking, and swimming in captive polar bears, to better estimate the energy demands of free-ranging polar bears; 3) measure the field metabolic rates, behaviors, and foraging rates of free-ranging polar bears on the spring sea ice; and 4) evaluate the ability of tri-axial accelerometers to measure the energy expenditure of free-ranging polar bears. In this dissertation, I develop methods using tri-axial accelerometers to remotely discriminate the behaviors (Chapter 1) and index the energy expenditure (Chapter 5) of free-ranging polar bears. I further find that polar bears have energetic costs of walking that are commensurate with other quadrupedal mammals (Chapter 2), but appear to have high energetic costs of swimming similar to other semi-aquatic mammals (Chapter 3). Additionally, similar to other large carnivores, polar bears have high resting metabolic rates and high field metabolic rates (Chapter 4). Of nine polar bears monitored on the spring sea ice of the Beaufort Sea, five of these bears had energy deficits as a result of their high energy demands and low foraging success (Chapter 4). These findings highlight the physiological constraints of these large apex carnivores and reinforce their reliance on energy-dense pagophilic seal prey. Furthermore, these findings elucidate the implications of increases in the frequency of spring fasting on polar bear body composition. Given their large body size and hypercarnivory, polar bears appear to be poorly suited to cope with rapid environmental change. The metrics developed in this dissertation provide a framework to monitor polar bear behaviors and energy expenditure to aid conservation and management of the species.