Temporal Variation in Japanese Macaque Bodily Mass

We investigated the bodily mass of infants and postpartum adult females longitudinally in provisioned free-ranging Japanese macaque (Macaca fuscata) troops of the Takasakiyama Natural Zoo, Oita, Japan. We investigated whether the rate of mass change in postpartum adult females and infants is more strongly associated with season (or calendar date) as opposed to the length of time since delivery/birth. Focal adult females' postpartum mass ranged between 7 and 10 kg for a year after delivery. For postpartum adult females, calender date (season) influenced the rate of mass change more than the length of time since delivery did. Rate of mass change in postpartum adult females was high in October (autumn) and April and May (spring) and low between December and February (winter). This may reflect seasonality in energy and protein intake from natural foods. Infant mass increased steadily from birth. Mass of infants varied between individuals, some infants reached 2 kg by about 240 days of age, and others by about 400 days of age. It was unclear, however, whether the rate of mass change in infants was influenced more by age or calendar date (season). Differences in trends between adult females and infants may reflect, to some degree, differences in sources of energy intake, i.e. solid foods for adult females and suckling and solid foods for infants.