Seasonal variation in the feeding behavior and diet of Japanese macaques (Macaca fuscata yakui) in lowland forest of Yakushima

The feeding behavior of the southern subspecies of Japanese macaque (Macaca fuscata yakui) was studied over a period of 18 months in warm temperate broad‐leaved forest on the island of Yakushima, Japan. Focal animal data were collected for the eight adults in the troop. Over a full annual cycle, 35.0% of foraging on identified foods was on leaves and shoots, 30.2% on fleshy fruit, 13.2% on seeds, and 5.5% on flowers. Invertebrates and other animal matter accounted for 10.3% of foraging and fungi for 4.6%. There was marked seasonal variation in the use of different food categories, and seeds, leaves, fleshy fruit, and animal matter were each predominant at different times of year. There was also evidence of annual cyclicity in patterns of foraging on all major food types. The monkeys spent less time moving and ate a greater variety of foods when feeding on leaves than when feeding on fruit and seeds, or on insects. Time spent foraging was positively correlated with diversity of the diet, but there was no simple relationship between time spent foraging and the predominant food type. This suggests that a wide variety of foods takes longer to harvest and process, irrespective of the food type. The diet of the study troop was flexible and could not be assigned to a simple dietary category, such as frugivorous or folivorous. If these data are representative of the subspecies, the Yakushima macaque is much more of a dietary generalist than most primates for which there are adequate data. Am. J. Primatol. 43:305–322, 1997. © 1997 Wiley‐Liss, Inc.