The post-emergence period for denning Polar Bears: phenology and influence on cub survival

• Published in: Journal of Mammalogy
• Main Authors: Andersen, Erik M, Wilson, Ryan R, Rode, Karyn D, Durner, George M, Atwood, Todd C, Gustine, David D
• Other Authors: Wang, Guiming, U.S. Fish and Wildlife Service, Coastal Impact Assistance Program, National Fish and Wildlife Foundation, Detroit Zoological Association, Selawik National Wildlife Refuge, Red Dog Mine, Teck Alaska Inc., Ecosystems Mission Area, USGS Changing Arctic Ecosystems Initiative, USGS Ecosystems and Climate and Land Use Change Mission Areas, Bureau of Land Management, Bureau of Ocean Energy Management, National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2024
• Subjects: Chukchi Sea; Beaufort Sea; Chukchi; Sea ice; Ursus maritimus
• Online Access: http://dx.doi.org/10.1093/jmammal/gyae010; https://academic.oup.com/jmammal/article-pdf/105/3/490/57830594/gyae010.pdf

Abstract Among polar bears (Ursus maritimus), only parturient females den for extended periods, emerging from maternal dens in spring after having substantially depleted their energy reserves during a fast that can exceed 8 months. Although den emergence coincides with a period of increasing prey availability, polar bears typically do not depart immediately to hunt, but instead remain at the den for up to a month. This delay suggests that there are likely adaptive advantages to remaining at the den between emergence and departure, but the influence of the timing and duration of this post-emergence period on cub survival has not been evaluated previously. We used temperature and location data from 70 denning bears collared within the Southern Beaufort Sea and Chukchi Sea subpopulations to estimate the phenology of the post-emergence period. We evaluated the influence of various spatial and temporal features on duration of the post-emergence period and evaluated the potential influence of post-emergence duration on litter survival early in the spring following denning. For dens that likely contained viable cubs at emergence (n = 56), mean den emergence occurred on 16 March (SE = 1.4 days) and mean departure on 24 March (SE = 1.6 days), with dates typically occurring later in the Chukchi Sea relative to Southern Beaufort Sea and on land relative to sea ice. Mean duration of the post-emergence period was 7.9 days (SE = 1.4) for bears that were observed with cubs later in the spring, which was over 4 times longer than duration of those observed without cubs (1.9 days). Litter survival in the spring following denning (n = 31 dens) increased from 0.5 to 0.9 when duration of the post-emergence period increased by ~4 days and other variables were held at mean values. Our limited sample size and inability to verify cub presence at emergence suggests that future research is merited to improve our understanding of this relationship. Nonetheless, our results highlight the importance of the post-emergence period in ...