Assessing past and future climatic influences on the availability of polar bear maternal denning habitat on Wrangel Island

Long-term changes in environmental conditions resulting from climate change may negatively affect reproductive success and lead to population-level consequences for species, especially those living at higher latitudes. Throughout their range, female polar bears (Ursus maritimus) typically require snowdrifts, either on the ice or land, to excavate maternal dens. In the Chukchi Sea (CS) subpopulation, 84% of dens have been reported to on land and 68% of these on Wrangel Island, Russia. Therefore, availability of suitable den habitat on Wrangel Island is critical for the long-term persistence of the CS subpopulation. We performed a retrospective analysis (1980–2020) of the availability of snowdrifts on Wrangel Island to estimate how the timing and distribution of snowdrifts suitable for denning has changed over this period. We evaluated the spatial distribution and availability of potential denning habitat across Wrangel Island from 1 September until 15 December and documented changes in snow conditions through time. We used sensitivity simulations under variable temperature increases associated with climate change projections to predict how availability of potential denning habitat on Wrangel Island might change in the future. We found no trends in spatial or temporal availability of modeled den habitat over the past 41 years. A projected 7.6 °C rise in temperature relative to current conditions resulted in a ∼50% reduction of denning habitat. If temperatures increase ≥13.6 °C relative to current conditions, 100% of denning habitat would be lost. Despite rising temperatures and sea ice loss, the climate of this area is cold enough that availability of denning habitat is not an immediate limiting factor for the CS subpopulation.