The effects of traffic on the raccoon dog (Nyctereutes procyonoides viverrinus) and other mammals in Japan

We investigated the extent of raccoon dog roadkills, and the factors influencing them, using data from the National Expressways in Japan for 1987-1998. A high rate of raccoon dog roadkills occurred in western Japan, whereas a relatively low rate was typical of the central region and of Hokkaido. Kills on the National Expressways increased as traffic and the length of the road network increased between 1987 and 1998. The relationship between mortality and traffic volume was scale-dependent. The number of roadkills was positively correlated with traffic volume at national level, but negatively correlated with the amount of traffic along sections of an individual major road between exits. There were spring and autumn peaks, and possibly early morning and evening peaks, of mortality. Mortality was higher for roads in a cutting, where the road was closer to water, and where the roadside habitat was broad-leaved woodland. Coniferous forest was negatively associated with roadkills. The total numbers of roadkills on four types of roads (National Expressways, National, Prefectural, and Municipal roads), was estimated to be between 110,000 and 370,000 in 1998. We suggest some preventative measures which might mitigate road casualties (while remaining attentive to human safety). Roadkill data, after controlling for traffic volume, can be useful as a population trend index. Patterns for racoon dogs are compared with those for other species.