1. Wildlife Research Center, Kyoto University, Kyoto 606-8203, Japan
2. Research and Development Section, Anicom Speciality Medical Institute Inc., Yokohama 231-0033, Japan
3. Department of Psychology, Graduate School of Letters, Kyoto University, Kyoto 606-8501, Japan
4. Japan Society for the Promotion of Science, Tokyo 102-0083, Japan
5. Department of Animal Science and Biotechnology, Azabu University, Yokohama 252-5201, Japan