Densities and habitat selection of the sika deer and the Japanese serow in Nikko National Park, central Japan, as revealed by aerial censuses and GIS analysis

抄録

Using infrared sensing and visual observations, ten helicopter censuses of the sika deer Cervus nippon and the Japanese serow Capricornis crispus populations in the southern part of Nikko National Park were conducted between December 1995 and February 1999. The data collected were used to estimate densities and distribution of the ungulates and to analyze their habitat selection with the help of GIS. The density of sika deer ranged between 11.6 and 33.1/km² in Omote Nikko, Ashio, and Tone, while in Oku Nikko it fluctuated between 1.9 and 11.3/km². The animals preferred mid elevations, gentle slopes and areas distant from roads. In winter (February and March) they strongly avoided northern and western exposures, whereas in late autumn (November and December) all aspect classes were used in accordance to their availability. The habitat selection by sika deer in Nikko National Park appeared to be affected primarily by human activity in late autumn and by snow depth in winter. Serows were observed only sporadically and their density did not exceed 1.0/km². They selected steep slopes and areas close to roads, seemingly in order to avoid sika deer. Comparison of the present sika deer density and distribution with earlier data suggests that their population has already reached carrying capacity in the traditional wintering range and its further increase will be realized by expanding the winter distribution range if global warming continues and the current hunting policy is not changed. In contrast to the situation amongst the sika deer, the Japanese serow population in Nikko National Park is undergoing a serious decline due to competition with sika deer. The utility of aerial surveys as a method for estimating wildlife populations in Japan is also discussed.