FORAGING STRATEGIES OF YAKUSHIMA MACAQUES (MACACA-FUSCATA YAKUI)

I investigated the activity budget and diet of Yakushima macaques (Macaca fuscata yakui) in warm temperate broad-leaved forest of Yakushima, Japan. Both time spent feeding and time spent moving varied considerably between half-months. However total time spent in active behaviors-feeding time plus moving time-was stable. The composition of the diet also showed considerable variation between half-months. The macaques fed mainly on fruits, seeds, mature leaves, fallen seeds, flowers, and young leaves, each of which accounted for more than 30% of feeding time in at least 1 half-month. They also ate insects and fungi, but each of them comprised less than or equal to 25 and less than or equal to 8% of feeding time in any half-month, respectively. Time spent feeding on mature leaves, young leaves, flowers, or fallen seeds is positively correlated with total time feeding and is negatively correlated with time moving. In contrast, time feeding on fruits, seeds, insects or fungi is negatively correlated with time feeding and is positively correlated with time moving. Foraging on foods that have a low energy content, a high density, and a relatively even distribution-mature leaves-or that need much manipulation to be processed-flowers and fallen seeds-increased feeding time, while foraging on foods for which monkeys must search intensively in the forest-fruits, seeds, insects, and fungi-led to increased moving time. I examined foraging strategies of Yakushima macaques in terms of moving costs and the quality of food items. Regarding time feeding on fruits, which have more energy and may need less manipulation than other foods, as a benefit and moving time as a cost, they seemed to employ a strategy that balanced the costs and benefits of foraging.