Alpine ericaceous dwarf shrubs as summer food resources for Asiatic black bears in Japan

Abstract

Abstract: The Asiatic black bear (Ursus thibetanus) is known to use the fruits of various fleshy-fruited plant species as food resources. However, there is no published evidence regarding whether they feed on the berries of 4 ericaceous dwarf shrub species that are widely distributed in alpine regions in Japan (Empetrum nigrum, Vaccinium uliginosum, Gaultheria pyroloides, and Vaccinium vitis-idaea). We assessed the use of, and preference for, these berries by black bears and identified the production and morphological and nutritional characteristics of these berries in the alpine zone of Mt. Asama, central Japan. Using camera-trap survey and scat analyses between July and November in 2017, 2018, and 2019, we obtained the first evidence that these bears consume large quantities of E. nigrum berries in the alpine zones during the summer. The density of berries per square meter was highest for E. nigrum. By contrast, the cost–benefit ratio of morphological fruit attractiveness (i.e., fresh pulp weight and dry pulp weight divided by total fresh seed weight per fruit), crude protein, crude fat, and nitrogen-free extract levels were lowest in E. nigrum berries. Therefore, fruit use by black bears appeared to be influenced by fruit production rather than the morphological or nutritional value of the fruits. Bears may compensate for this nutritional deficit by consuming large quantities of these berries. Consequently, E. nigrum berries are key food items for black bears in Japan and may compensate for summer food shortages.