title: Animal physiology. Summer declines in activity and body temperature offer polar bears limited energy savings.
abstract: Polar bears (Ursus maritimus) summer on the sea ice or, where it melts, on shore. Although the physiology of "ice" bears in summer is unknown, "shore" bears purportedly minimize energy losses by entering a hibernation-like state when deprived of food. Such a strategy could partially compensate for the loss of on-ice foraging opportunities caused by climate change. However, here we report gradual, moderate declines in activity and body temperature of both shore and ice bears in summer, resembling energy expenditures typical of fasting, nonhibernating mammals. Also, we found that to avoid unsustainable heat loss while swimming, bears employed unusual heterothermy of the body core. Thus, although well adapted to seasonal ice melt, polar bears appear susceptible to deleterious declines in body condition during the lengthening period of summer food deprivation.
authors.affiliation: Program in Ecology, University of Wyoming, Laramie, WY 82071, USA. Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Whiteman
authors.affiliation: Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Harlow
authors.affiliation: U.S. Geological Survey, Alaska Science Center, Anchorage, AK 99508, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Durner
authors.affiliation: Department of Statistics, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: R
authors.initials: R
authors.lastname: Anderson-Sprecher
authors.affiliation: Wyoming Geographic Information Science Center, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Albeke
authors.affiliation: Marine Mammals Management, U.S. Fish and Wildlife Service, Anchorage, AK 99503, USA.
authors.forename: E V
authors.initials: EV
authors.lastname: Regehr
authors.affiliation: Polar Bears International, Bozeman, MT 59772, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Amstrup
authors.affiliation: Program in Ecology, University of Wyoming, Laramie, WY 82071, USA. Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ben-David
mesh_terms: D000818:Animals; D001831:Body Temperature; D057231:Climate Change; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006605:Hibernation; D046448:Ice Cover; D008297:Male; D012621:Seasons; D001503:Ursidae / Q000378:metabolism / Q000502:physiology*