Abstract 108 – Behavioral Characteristics of Autumn Migration in Solitary Terrestrial Mammals

Tamako Makino, Seungyun Baek, Akino Inagaki, Naoki Takekoshi, Koji Yamazaki,
Shinsuke Koike

Migration is the periodic seasonal movement between remote areas of activity and there are
some differences depending on internal factors’ characteristic of individuals. About energy
spent, the movement between areas("commuting phase")is more demanding compared with
movement within the area("wandering phase"), especially for terrestrial mammals. Thus,
gregarious mammals that make annual migrations between fixed locations apply social learning
and memory for selecting energy-efficient(linear) paths. However, for solitary species, or for
species whose migratory behavior varies, the behavioral characteristic of migration is likely to
vary among individuals or years. Some black bears(Ursus thibetanus)("bears")migrate from late
summer to fall in years when locally hard masts are poor. This study aims to elucidate the
behavioral characteristic of autumn migration of bears. We used three factors: aging, number
of poor masting during the subadult period, and sex, to determine whether experience affects
the energy efficiency of commuting phase. 18 years of migration data obtained by attaching
GPS collars to bears in Ashio and Nikko mountains in Japan and 29 years of masting data on
Quercus crispula were used in this study. Analysis of data from 43 bear years(29 male
individuals)and 53 bear years(25 female individuals)demonstrated that bears migrated faster
and more linearly during the commuting phase than during the wandering phase and that
males migrated more linearly than females. In addition, with increasing age and the number of
poor masting experienced, the commuting paths of bears were more linear. One reason for this
is that with age, bears accumulate memory, thereby increasing the number of areas they have
traveled to and from. We think the experience acquired during the subadult period contributes
specifically to memory. A possible reason for the more linear migration of males compared with
females is that males are larger than females and as have greater mobility.