Movement patterns and space use of maternal grizzly bears influence cub survival in Interior Alaska

Foraging decisions and movement strategies by animals often involve a trade-off between meeting nutritional demands and minimizing risk of predation. We evaluated the influence of space use and movement patterns of maternal female grizzly bears (Ursus arctos) on cub (defined as first year of life) survival in eastern Interior Alaska, USA, during 2008-2012. We monitored 9 GPS radiocollared females that produced 28 cubs in 12 litters ((x) over bar litter size = 2.3, range = 2-3). The estimated annual cub survival rate was 0.39 (95% CI = 0.20-0.57). In all cases the entire litter survived or died prior to den entrance. All cubs in a litter died either concurrently or within 14 days in 5 of 7 litters lost. Sixty-nine percent of cub mortality occurred between 31 May and 16 June. We did not document cub mortality before 31 May. Females with surviving cubs remained within 1 km of the den for a longer period following emergence than those that lost cubs. Between den emergence and the onset of vegetation green-up, females with surviving cubs used fewer habitat patches and remained in individual habitat patches longer than females that lost their cubs later in the summer. Females with surviving cubs exhibited different activity patterns compared with females that lost their cubs, particularly by moving less between midnight and mid-morning during 15 May-16 June. Once vegetation green-up occurred, movement rates of all maternal females were similar except that females with surviving cubs continued to move less during the morning hours (0000-1200 hr). We did not find evidence that the body size of the mother was a factor explaining cub survival nor was there evidence that cub survival was directly influenced by human causes. The most successful behavioral strategies used by maternal females to maximize cub survival appeared to be a combination of limiting movements to a few habitat patches between den emergence and vegetation green-up and limiting activity between midnight and mid-morning. We suggest that the ability to find and exploit suitable habitat patches during this period of limited resources may have allowed females to alter movements temporally and spatially and provision themselves and their cubs more effectively. This strategy was likely effective for both minimizing exposure to infanticidal adult bears and allowing cubs to maximize energy efficiency.