Kevin R. Middel, Martyn E. Obbard
Ursus 2024 (35e17), 1-27, (24 September 2024) https://doi.org/10.2192/URSUS-D-23-00019R1
KEYWORDS: home range, movement patterns, polar bear, sea ice, seasonal movements, Southern Hudson Bay, space use, Ursus maritimus
To access seals (Pinnipedia), polar bears (Ursus maritimus) move large distances over the sea ice in winter. Already documented declines in ice duration for Hudson Bay, Canada, are predicted to continue, likely affecting polar bear movement patterns. Using data from global positioning system (GPS) collars, 2007–2011, we describe movement patterns of adult female polar bears of the Southern Hudson Bay (SH) subpopulation. We tested effects of season and reproductive class on movement rates, distance travelled, displacement distance and direction, and home range size. Except for denning females, reproductive class had no effect on movement rates, which were greatest during freeze-up and least during summer. Across all reproductive classes and seasons, mean hourly movement rate was 0.63 km/hour. Mean annual distance moved by nondenning females was 4,771 km. During freeze-up, bears moved north-easterly from the Ontario coast toward the Belcher Islands and Québec following the forming ice edge. During breakup, bears moved southerly toward the Ontario coast and away from the residual ice that occurs north of the Ontario coast. In autumn, denning females moved southerly and inland to den. Mean annual minimum convex polygon (MCP) home-range size was 153,866 km2, with no effect of reproductive class nor change over time. Home range estimates from kernel density estimators and Brownian bridge movement models (BBMM) varied by reproductive class and were smaller than MCP ones. The BBMM estimates likely yield more realistic patterns of space use by polar bears. Using data from satellite collars, 1997–2003, we compared travel distance and home range size between periods (1997–2003; 2007–2011). We found weak evidence of a difference in distance moved between periods, perhaps due to a period of ice stability in the 2000s. Our results identified patterns of use of extensive areas of Hudson Bay by SH bears in winter, and results provide benchmarks for future studies of movement patterns.