Relation between age–sex classes and dietary selection of wild Japanese monkeys

Dietary selection by wild Japanese monkeys ( Macaca fuscata yakui Kuroda) was examined in relation to body size. The monkeys were classified into three age–sex categories: adult males, adult females and immatures excluding suckling infants. Time spent feeding did not differ between age–sex classes, although time spent moving was longer in lighter classes. Heavier individuals fed relatively more on mature leaves, while lighter individuals fed on insects more frequently. Mature leaves were more abundant but had lower energy content than other food items in the forest. Heavier monkeys seemed to feed on greater amounts of lower quality food in this species. This finding agrees with the Jarman–Bell principle on ungulates.