Whitebark Pine (Pinus albicaulis) seeds as food for bears (Ursus spp.) in Banff National Park, Alberta

Abstract

The large, nutrient-rich seeds of Whitebark Pine (Pinus albicaulis Engelmann) are important food for bears (Ursus spp.) in Yellowstone National Park. In Banff National Park, studies have shown that American Black Bears (Ursus americanus) eat these seeds, but little additional information is available. We studied Whitebark Pine in Banff National Park to address this information gap. Because bears obtain Whitebark Pine seeds from Red Squirrel (Tamiasciurus hudsonicus) middens, our objective was to measure the abundance, habitat characteristics, and use by bears of middens in Whitebark Pine forests. A second objective was to determine whether Grizzly Bears (U. arctos) in Banff National Park also eat Whitebark Pine seeds. In 2011–2012, we ran 29 ha of 20–50 m wide transects at 10 sites with accessible Whitebark Pine stands and found 0–3.7 middens/ha (mean 1.23, SD 1.17, n = 10). Midden density was weakly related to total basal area of all conifers but not to basal area of Whitebark Pine. Middens were located in the upper subalpine at an average elevation of 2110 m (SD 90, n = 8) on 41–248° facing slopes with a mean steepness of 28° (SD 5, n = 8). Bears had excavated middens at all eight sites where we found middens; at the remaining two sites, middens did not occur within our transects. Overall, 24 (67%) of the 36 middens located in our transects had been dug by bears. In October 2013, we searched areas where three global positioning system (GPS)-collared Grizzly Bears had been located in late September 2013 and found five recently dug middens located less than 6 m from GPS fixes. These observations are, to our knowledge, the first conclusive evidence that grizzly Bears in Banff National Park eat Whitebark Pine seeds. Because Whitebark Pine occurs at high elevations on steep slopes where human use is low, this resource may be important in keeping bears in habitat where risk of human-caused mortality is lower. Our results may assist managers responsible for conservation of bears in Banff National Park, where both American Black Bears and Grizzly Bears are subject to high levels of human-caused mortality.