The daily activity rhythm in a troop of wild Japanese monkey

An assessment of the daily activity rhythm of wild Japanese monkeys was tried both from the calculation of the proportion that each activity occupied in the total activities and the “nomadograph,” representing temporary change in the pace of the daily movement. Seasonal and day-to-day changes are recognized in the daily activity rhythm of the troop of wild Japanese monkeys. It seems that seasonal change in the daily activity rhythm corresponds to the seasonal fluctuation of food supply and atmospheric temperature. From autumn to early winter, when much food is available, a clear-cut pattern of activity emerges; namely, three intensive feeding periods are recognized in a day. Moreover, day-to-day variation in the activity rhythm is fairly small and the activity pattern thus becomes standardized. In winter, when least food is available, activity of monkeys drops to the lowest level of the year. Day-to-day variation in the activity rhythm is great. Two to four intensive feeding periods in a day are recognized. In early spring and summer, when food supply is rather scarce, there exist two to three intensive feeding periods in a day. During the heat of the day in summer, activity of monkeys is conspicuously low.