Polar bears live on sea ice that floats over the Arctic Ocean and that forms and melts each year within bays and among islands in eastern Canada. This sea ice habitat is critical for providing polar bears a way to access seals, their primary prey. Polar bears hunt seals where they come up to breathe at holes in the ice and when they haul out onto the ice to have their pups. The blubber of seals is the primary energy source for polar bears throughout the Arctic. A changing Arctic climate has already reduced the amount of sea ice that bears can use to access seals, and continued warming of several degrees over the next 100 years is expected to further decrease sea ice during the summer and early fall in many parts of the Arctic. With less ice, polar bears across much of the Arctic are spending more time on land where they cannot access seals. Although polar bears have been observed feeding on nesting geese and seabirds, berries, and vegetation, these foods are more disbursed and less-energy rich than the typical prey of polar bears. Thus, land-based foods may not occur in sufficient quality, quantity, or distribution to ensure the current widespread distribution of polar bears. This study seeks to better understand bear behavior on land and the degree to which land-based foods meet the energetic needs of polar bears. The question of whether bears lose or maintain their body mass for extended periods on land is critical to determining potential effects of sea ice loss on birth and death rates – information that most Arctic nations need to manage their resident polar bears. Because polar bears occur at the top of the Arctic food chain, they are also a key indicator species for changes in the Arctic as well as an iconic symbol of the effects of a changing climate. Our results will help identify actions to further protect this species and the communities whose cultures and safety are closely linked to the behavior of this Arctic predator.
The goals of this study are to determine the behavior and energetic balances of polar bears while summering on land. We are proposing to 1) quantify the degree to which foods consumed while on land meet the energetic needs of polar bears and 2) thereby provide the information necessary to understand the implications of increasing warming, sea ice loss, and land use on polar bear well-being and population dynamics across the Arctic. We will do this by measuring energy expenditure, weight change, fat and protein composition of the weight change, activity and movement rates, and feeding behavior of males and females, young and old while they are on land. We will estimate the amount of energy coming from food as the difference between the energy expenditure measured with doubly labeled isotopic water and the energy released when body fat and protein are mobilized. If these values are equal, no useful energy is coming from food. If the energy expenditure measured with doubly labeled water is higher than that available from mobilized protein and fat, then that difference is the amount of energy coming from ingested food. These measurements can only be done with the most advanced techniques available for human and animal research. These techniques include 1) GPS collars with built in video cameras that will allow us to accurately track bear movements and directly observe what they are doing and eating and 2) an isotopic water dilution technique that allows measurement of the number of calories they burn and how much fat and protein they gain or lose between two captures which will be about 21 days apart. These techniques will allow us to determine the implications of polar bears increasingly using land as their sea ice habitat continues to decline. Thus, this study will provide information for understanding the future of polar bear populations, a significant part of Arctic food web, in a warming Arctic.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
