To know population size is important for managing sika deer. Beam light census is 1 method to monitor deer population size. To answer what and how the census results tell remains problem. Former studies estimated population size by the relationship among discovery rate, distance to animal, and visibility commonly.

We carried out the census in northwestern Mount Fuji, from July 2000 to July 2002. Survey line started at 1200m and ended at 1800m in elevation, total distance was 15.8km. We did the survey by 1 driver and 2 light holders. We drive a jeep at 10km/h along road and recorded site, number, sex, ages (adult, juvenile, fawn), behavior (feeding, resting), and the distance of deer to jeep.

Deer number changed seasonally with 2 peaks at May and Sept.-Oct.. Both peaks were coincidence with active feeding period. Further deer mainly appeared in <15-year planted forest. This suggests that newly planted areas are main feeding sites due to high food availability. Buck mainly appeared from Oct.-Nov., the rutting season. This suggests that bucks might use different habitat except rutting period. The total deer number found during the survey was not only influenced by visibility and discovery rate, but also influenced by behavior, habitat use, and food distribution. Therefore, the census result may only be relative density method.