Detection of arboreal feeding signs by Asiatic black bears: effects of hard mast production at individual tree and regional scales

Abstract Arboreal feeding signs are among several field indicators of the use of tree crowns by the Asiatic black bear ( Ursus thibetanus ) to sit and eat fruit; however, it is unclear which factors influence this sign formation in hard mast species. Here, we investigated the influence of seed production by individual trees and at a regional scale by major hard mast species on the detection of arboreal feeding signs. For 7 years, we quantitatively assessed seed production by 374–481 trees each year of three dominant hard mast species ( Quercus crispula , Quercus serrata and Castanea crenata ) in the Ashio‐Nikko Mountains of central Japan and checked for the presence or absence of arboreal feeding signs in these trees. We estimated individual tree energy values and regional mast energy values across these three species and evaluated the influence of each factor on the detection probability of arboreal feeding signs. Arboreal feeding signs were more likely in individual trees with larger mast energy values and during poor mast years. There was no difference among species in the relative importance of individual tree energy or regional mast energy. Interaction of factors was also detected: the magnitude of the positive effect of individual tree energy on the detection of arboreal feeding signs was larger in poorer mast years, and the negative effect of regional mast energy was more conspicuous in the case of trees with greater mast energy. Thus, bears may maximize their feeding efficiency on hard mast in various ways, depending on regional mast availability; during poor mast years, bears are more likely to climb trees with higher individual tree energy values and leave arboreal feeding signs. Arboreal feeding signs cannot be used as an indicator of bear density unless both individual tree energy and regional mast energy values are monitored.