INFLUENCE OF SEA ICE DYNAMICS ON HABITAT SELECTION BY POLAR BEARS

Abstract

Polar bears live in high-latitude environments characterized by cyclic variation in form and extent of sea ice. From 1991 to 1995, we used radio telemetry and monthly satellite images to compare patterns of ice selection by 110 female polar bears, relative to two geographic regions and four seasons. We hypothesized that extreme seasonal changes in ice characteristics in the Baffin Bay region, including a period of open water, may limit polar bear density despite supporting greater prey density than the Archipelago region, where ice is present year-round. Using cyclic time series analysis to model seasonal variation, we found differences in level, amplitude, and phase between sea ice characteristics and habitat selection by polar bears of the Arctic Archipelago and Baffin Bay regions. Polar bears not only followed seasonal changes, but they anticipated seasonal fluctuations, e.g., polar bears were found close to ice edges in spring in advance of the peak availability of edges. Also, seasonal selection of sea ice by polar bears was generally of a larger amplitude than cycles in ice and is best explained by intensive use of specific ice types in spring and summer, and sparse use during the remaining year. During spring and summer, Archipelago bears used landfast ice more intensively, whereas Baffin bears used moving ice, defined as thick first-year ice found in large floes. Both ice types likely represent areas where most seal pupping occurred in spring for each region. Bears from both regions selected first-year ice in winter when new ice was forming and multiyear ice in autumn when maximum ice melt had occurred. Overall, polar bear selection of ice habitat was similar between regions despite major differences in seasonal ice characteristics. Polar bear density may not directly relate to prey density, due to the limited ability of bears to track the extreme seasonal fluctuations in ice extent found in more productive environments.