1Department of Anthropology, Rutgers, The State University of New Jersey, 2Anthropological Institute and Museum, University of Zurich
Friday Afternoon, Ballroom B
Due their low productivity, the peat-swamp forests of Central Kalimantan are challenging environments for large, arboreal frugivores like the orangutan. For adult female orangutans with dependent offspring, obtaining enough energy to support lactation is expected to be difficult, particularly during periods of low fruit availability. However, little is known about how female primates modify their caloric intake to support dependent offspring. We examined variation in Bornean orangutan daily caloric intake in relation to fruit availability and reproductive state at the Tuanan Field Station, an alluvial, peat-swamp habitat. We predicted that caloric intake would increase with fruit availability and that adult females with dependent offspring would have higher caloric intake compared to solitary adult females. We examined 1,707 nest-to-nest focal follows collected from 2003 to 2008 using Generalized Linear Mixed Models. We found a positive relationship between fruit abundance and daily caloric intake (p<0.0001). Adult females with dependent offspring and immature independent females consumed significantly more calories compared to adult females without dependent offspring during periods of high and middle fruit availability, but not when fruit availability was low. During periods of low caloric intake, individuals appear to have less flexibility in the amount of calories consumed. Our results suggest that females with dependent offspring increase their daily intake to account for extra calories lost to lactation, but this strategy is not possible when fruit availability is low. Instead, we suggest that during these periods, lactating females rely on body fat stores and tissues to support their offspring.