1. Laboratory of Wildlife Management Tokyo University of Agriculture and Technology 3‐5‐8 Saiwai‐cho, Fuchu Tokyo 183‐8509 Japan
2. Center for Health and Environmental Risk Research, National Institute for Environmental Studies 16‐2 Onogawa, Tsukuba Ibaraki 305‐8506 Japan
3. Kanagawa Prefecture Nature Conservation Center 657 Nanasawa Atsugi Kanagawa 243‐0121 Japan