Feeding rates and energy deficits of juvenile and adult Japanese monkeys in a cool temperate area with snow coverage

Abstract

Japanese monkeys, Macaca fuscata , living in a cool temperate forest experienced energy crises in winter. We measured feeding times and feeding rates (mass of foods eaten per unit time of feeding) in six different‐sized, age–sex classes (1.2–12.6 kg body mass) in autumn and winter. One‐, 2‐ and 3~4‐year‐olds spent 34–35% and 44–46% of the day feeding in autumn and winter, respectively. Monkeys less than 0 years old spent less time feeding (16–28%) than average in winter and autumn; adult females spent less (41%) in winter; and adult males spent less (25%) in autumn. All age–sex classes ate mainly fruits in autumn and the heavier classes fed more on tree bark than buds in winter. The feeding rate for fruits (2.3–53.5 g min −1 ) was nine to 12 times faster than those for buds (1.0– 4.8 g min −1 ) and bark (0.5–4.4 g min −1 ), and energy content did not differ among fruits (22.1 kJ g −1 dry mass), buds (19.9 kJ g −1 dry mass) and bark (23.2 kJ g −1 dry mass). Energy base feeding rates increased with body mass where the body mass exponent for buds (0.29) was smaller than those for bark (0.64) and fruits (0.63), which might be attributable to the unit size of food items and mass dependency of masticatory apparatus. Our monkeys obtained two to five times more energy in autumn (1567–1150 kJ day −1 ) than in winter (604–3020 kJ day −1 ). Adult females obtained 60% of expected energy expenditure and other classes obtained 77–88% of that in winter.

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