Recent reductions in thickness and extent have increased drift rates of Arctic sea ice. Increased ice drift could significantly affect the movements and the energy balance of polar bears (Ursus maritimus) which forage, nearly exclusively, on this substrate. We used radio-tracking and ice drift data to quantify the influence of increased drift on bear movements, and we modeled the consequences for energy demands of adult females in the Beaufort and Chukchi seas during two periods with different sea ice characteristics. Westward and northward drift of the sea ice used by polar bears in both regions increased between 1987–1998 and 1999–2013. To remain within their home ranges, polar bears responded to the higher westward ice drift with greater eastward movements, while their movements north in the spring and south in fall were frequently aided by ice motion. To compensate for more rapid westward ice drift in recent years, polar bears covered greater daily distances either by increasing their time spent active (7.6%–9.6%) or by increasing their travel speed (8.5%–8.9%). This increased their calculated annual energy expenditure by 1.8%–3.6% (depending on region and reproductive status), a cost that could be met by capturing an additional 1–3 seals/year. Polar bears selected similar habitats in both periods, indicating that faster drift did not alter habitat preferences. Compounding reduced foraging opportunities that result from habitat loss; changes in ice drift, and associated activity increases, likely exacerbate the physiological stress experienced by polar bears in a warming Arctic. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.
资助项目:
Primary funding for this research was provided by the U.S. Geological Survey, Ecosystems and Climate and Land Use Change Mission Areas. Additional support was provided through a National Science Foundation Grant (OPP 0732713) to the University of Wyoming
; the United States Fish and Wildlife Service, Marine Mammals Management and the Arctic National Wildlife Refuge
; Environment and Climate Change Canada
; the North Slope Borough, Department of Wildlife Management
; the Northwest Territories Department of Resources, Wildlife and Economic Development
; the Polar Continental Shelf Project
; and the University of Alberta. This research was permitted under the Marine Mammal Protection Act and Endangered Species Act under FWS permit MA046081 and USGS permit MA 690038 and followed the protocols approved by Animal Care and Use Committees of the FWS, USGS (assurance no. 2010–3), the University of Wyoming, and the University of Alberta. We thank the numerous biologists and pilots whose efforts were essential for obtaining radiotelemetry data. The following individuals are recognized for their constructive input on prior versions of this manuscript: T. Atwood, G. Hilderbrand, M. Kaufmann, and J. Lovvern. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government.
U.S. Geological Survey, Alaska Science Center, Anchorage, AK, United States; U.S. Geological Survey, Alaska Science Center, Juneau, AK, United States; Wyoming Geographic Information Science Center, University of Wyoming, Laramie, WY, United States; Department of Zoology and Physiology, University of Wyoming, Laramie, WY, United States; Polar Bears International, Bozeman, MT, United States; Environment and Climate Change Canada, University of Alberta, Edmonton, AB, Canada; U.S. Fish and Wildlife Service, Marine Mammals Management, Anchorage, AK, United States