title: Costs of locomotion in polar bears: when do the costs outweigh the benefits of chasing down terrestrial prey?
abstract: Trade-offs between locomotory costs and foraging gains are key elements in determining constraints on predator-prey interactions. One intriguing example involves polar bears pursuing snow geese on land. As climate change forces polar bears to spend more time ashore, they may need to expend more energy to obtain land-based food. Given that polar bears are inefficient at terrestrial locomotion, any extra energy expended to pursue prey could negatively impact survival. However, polar bears have been regularly observed engaging in long pursuits of geese and other land animals, and the energetic worth of such behaviour has been repeatedly questioned. We use data-driven energetic models to examine how energy expenditures vary across polar bear mass and speed. For the first time, we show that polar bears in the 125-235 kg size range can profitably pursue geese, especially at slower speeds. We caution, however, that heat build-up may be the ultimate limiting factor in terrestrial chases, especially for larger bears, and this limit would be reached more quickly with warmer environmental temperatures.
authors.affiliation: Division of Vertebrate Zoology , American Museum of Natural History , 79th Street and Central Park West , New York , NY 10024 , USA.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Gormezano
authors.affiliation: Department of Natural Resources Science , University of Rhode Island , Kingston , RI 02881 , USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: McWilliams
authors.affiliation: Department of Wildland Resources and the Ecology Center , 5230 Old Main Hill , Utah State University , Logan , UT 84322-5230 , USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Iles
authors.affiliation: Division of Vertebrate Zoology , American Museum of Natural History , 79th Street and Central Park West , New York , NY 10024 , USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Rockwell
keywords: Ursus maritimus; locomotion; polar bear; predation; snow goose; terrestrial prey