Identifying shifts in maternity den phenology and habitat characteristics of polar bears (Ursus maritimus) in Baffin Bay and Kane Basin

Abstract

The phenology and habitat selection of polar bear (Ursus maritimus) maternity dens may change over time in response to shifting environmental conditions. This study compared satellite telemetry data on 40 adult females from the Baffin Bay subpopulation collected from 2009–2015, and 16 adult females from the Kane Basin subpopulation collected from 2012–2015 to previously published data on maternity and shelter dens from 1991–1997 in order to look for shifts in maternity den site characteristics and phenology. Sea ice has decreased markedly in the two study regions since the early 1990s. Our specific objectives were to: 1) identify den entry and exit dates using temperature and location data from satellite radio collars; 2) compute denning duration and compare the results to historical data from the 1990s; and 3) characterize and compare maternal den site habitat attributes between the two time periods. Comparison of the Baffin Bay maternity dens (1990s n = 8 dens; 2000s n = 16 dens) from the two periods revealed that mean denning duration shortened in the 2000s by an average of 27 days (mean = 167.1 days, SD = 27.6 days) compared to the 1990s (mean = 194.1 days, SD = 21 days). Delayed den entry in the fall was the primary reason for the shorter denning durations observed in the later decade (1990s median entry date = 28 August; 2000s median entry date = 3 October). Maternity dens in Baffin Bay differed significantly in elevation and slope (p = 0.003), with bears in the 2000s using denning areas at higher elevation and steeper slopes than in the 1990s. No significant difference in den phenology or habitat characteristics was found among the Kane Basin subpopulation. These results suggest significant changes in maternity den phenology and denning habitat selection in Baffin Bay over the past two decades. Shifts in the timing of melting sea ice and the absence of suitable snow conditions may explain the observed changes. This study offers a successful example of the use of satellite telemetry in detecting shifts in phenology and habitat selection for species that occupy remote habitats.