Andersen Erik M, Wilson Ryan R, Rode Karyn D, Durner George M, Atwood Todd C, Gustine David D
U.S. Fish and Wildlife Service, Marine Mammals Management, 1011 E. Tudor Road, Anchorage, AK 99502, United States.
U.S. Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK 99508, United States.
J Mammal. 2024 Mar 2;105(3):490-501. doi: 10.1093/jmammal/gyae010. eCollection 2024 Jun.
Among polar bears (), 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 ( = 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 ( = 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 contributing to reproductive success and can assist managers in developing conservation and mitigation strategies in denning areas, which will be increasingly important as human activities expand in the Arctic.
在北极熊中，只有即将分娩的雌性会长时间筑窝，它们在春季从母窝中出来，此前在长达8个月以上的禁食期内，其能量储备已大幅消耗。尽管出窝时间与猎物可获得性增加的时期相吻合，但北极熊通常不会立即离开去捕猎，而是会在窝边停留长达一个月。这种延迟表明，在出窝和离开之间留在窝边可能有适应性优势，但此前尚未评估这一出窝后时期的时间和持续时间对幼崽存活的影响。我们利用来自波弗特海南部和楚科奇海亚种群中70只佩戴项圈的筑窝北极熊的温度和位置数据，来估计出窝后时期的物候情况。我们评估了各种空间和时间特征对出窝后时期持续时间的影响，并评估了出窝后持续时间对筑窝后春季早期幼崽存活率的潜在影响。对于出窝时可能有存活幼崽的窝（n = 56），平均出窝时间为3月16日（标准误 = 1.4天），平均离开时间为3月24日（标准误 = 1.6天），楚科奇海的日期通常比波弗特海南部晚，且在陆地上的日期比在海冰上晚。对于春季晚些时候被观察到带着幼崽的北极熊，出窝后时期的平均持续时间为7.9天（标准误 = 1.4），这比未观察到幼崽的北极熊的持续时间（1.9天）长4倍多。当出窝后时期的持续时间增加约4天且其他变量保持在平均值时，筑窝后春季的幼崽存活率（n = 31个窝）从0.5提高到了0.9。我们有限的样本量以及无法在出窝时核实幼崽是否存在，这表明值得未来开展研究以增进我们对这种关系的理解。尽管如此，我们的结果凸显了出窝后时期对繁殖成功的重要性，并可协助管理人员制定筑窝区域的保护和缓解策略，随着北极地区人类活动的扩展，这将变得越来越重要。
