ORIGINAL ARTICLE Ami Nakajima • Shinsuke Koike • Takashi Masaki Takuya Shimada • Chinatsu Kozakai Yui Nemoto • Koji Yamazaki • Koichi Kaji Spatial and elevational variation in fruiting phenology of a deciduous oak (Quercus crispula) and its effect on foraging behavior of the Asiatic black bear (Ursus thibetanus) Received: 26 March 2011 / Accepted: 27 December 2011 / Published online: 1 February 2012 Ó The Ecological Society of Japan 2012 Abstract In habitats with elevational gradients, differ- ences in the fruiting phenology of a single key food resource may affect the feeding behavior of an animal. The objectives of the present study were to assess (1) whether or not fruiting phenology and characteristics of Quercus crispula acorns differed with changes in altitude (900–1,400 m asl) and area; (2) when bears foraged acorns in relation to their phenological development; and (3) where bears engaged in acorn foraging behavior with respect to acorn phenology. No difference in the fruiting phenology of acorns at various altitudes and locations was found, with the exception of changes in color and abscission period. Acorn abscission period occurred later at a site with an elevation of 1,200 m in Tochigi and at another with an elevation of 1,400 m in Gunma, making the available energy of acorns in the tree canopy (AET) greater and available for a longer time period at those two sites. Foraging of acorns by bears was observed at sites of moderate to high altitude between late September and mid-October. A threshold date when acorns became suitable for foraging by bears could not be identified, as the size and nutritional value of acorns increased continuously. Foraging activity of bears observed at moderate and high altitude sites cor- responded with locations where AET was available in greater amounts and for a longer period of time for some sites; however, the small sample size precluded accurate assessment. Keywords Feeding habit Æ Acorn Æ Quercus crispula Æ Elevational gradient Æ Japan Introduction Spatial and temporal variations in food environments affect habitat use by animals (e.g., Morrison et al. 1998). Due to the variations in fruit production among years that are observed in many tree species (Shibata et al. 2002), frugivores are known to change their habitat use (Schooley 1994). In addition to inter-annual variation, intra-annual variations (i.e., seasonal variations) in habitat use can also be observed. In temperate zones, plant phenology changes markedly with the seasons, limiting the flowering, leafing and fruiting periods, which impacts the feeding behaviors of both frugivores and herbivores (Hejl and Verner 1990; Costello and Sage 1994; Keane and Morrison 1999; Kuo and Lee 2003; Vernes et al. 2004; Naves et al. 2006). Furthermore, in habitats with elevational gradients, seasonal changes in the availability of food resources are often influenced by altitude, resulting in seasonal changes in the use of such environments by animals. For example, differences in vegetation based on altitude result in temporal changes in habitat use by birds (Loiselle and Blake 1991). Dif- ferences in the fruiting phenology of a single key species distributed over a broad elevational gradient may also have an effect on habitat use of specialist birds (Banko et al. 2002). Most of the Ursidae are omnivorous and have diets that depend largely on fruits. Like other frugivores, they change their home range as well as their habitat use A. Nakajima (&) Æ S. Koike Æ C. Kozakai Æ Y. Nemoto Æ K. Kaji Tokyo University of Agriculture and Technology, 3-5-8 Saiwai, Fuchu, Tokyo 183-8509, Japan E-mail: nimh42@hotmail.com Tel.: +81-423-675738 Fax: +81-423-675738 T. Masaki Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan T. Shimada Tohoku Center, Forestry and Forest Products Research Institute, 92-25 Nabeyashiki, Shimo-Kuriyagawa, Morioka, Iwate 020-0123, Japan K. Yamazaki Zoological Laboratory, Ibaraki Nature Museum, 700 Osaki, Bando, Ibaraki 306-0622, Japan Ecol Res (2012) 27: 529–538 DOI 10.1007/s11284-011-0919-z