1. Carnivore Ecology and Conservation Research Group, Tokyo University of Agriculture and Technology, Saiwaicho 3-5-8, Fuchu City, Tokyo 183-8509, Japan
2. Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
3. Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
4. Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, The Recanati-Kaplan Centre, Tubney House, Abingdon Road, Tubney, Oxon OX13 5QL, UK