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 shift over time in response to changing environmental conditions. We compared maternity den phenology and habitat characteristics using satellite telemetry data from adult female polar bears from the Baffin Bay (BB) (n = 16 dens; 2009–2015) and Kane Basin (KB) subpopulations (n = 3 dens; 2012–2015) to previously published maternity den data from 1991 to 1997 (BB n = 8 dens; KB n = 3 dens). BB maternity denning duration decreased from a mean of 194.1 days (SD = 21.0 days, n = 8) in the 1990s, to a mean of 167.1 days (SD = 27.6 days, n = 16; p = 0.017) in the 2000s. Delayed den entry accounted for shorter denning durations (1990s entry date $$\bar{x}$$ = 7 September; 2000s entry date $$\bar{x}$$ = 5 October; p = 0.018). For dens habitat characteristics of which could be measured, BB maternity dens in the 2000s occurred at higher elevations ( $$\bar{x}$$ = 707.0 m, SD = 284.9 m, n = 15; p = 0.003) and greater slopes ( $$\bar{x}$$ = 23.1°, SD = 7.4°; p = 0.003) than the 1990s (elevation $$\bar{x}$$ ± SD = 351.3 ± 194.5 m, n = 8; slope $$\bar{x}$$ ± SD = 11.9 ± 6.4°). Aspect also significantly differed between the 1990s ( $$\bar{x}$$ = 51.3°) and 2000s BB maternity dens ( $$\bar{x}$$ = 199.7°; Watson’s U 2 p = 0.042). KB dens were not statistically compared due to low sample size (n = 3 dens in both periods). Shifts in sea ice phenology and snow availability may explain the observed changes.