1Ecology & Evolution, Rutgers, The State University of New Jersey, 2Anthropology, Boston University, 3Anthropology, Rutgers, the State University of New Jersey
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Bornean orangutans (Pongo pygmaeus wurmbii) prefer to consume fruit but rely heavily on fallback foods when fruit is scarce. Although some fallback foods (e.g. leaves) have higher protein than fruits, previous research in a Dipterocarp forest has shown that the total amount of protein ingested per day is lower when fruit is scarce, primarily because the total amount of food consumed in lower. Very little is known about nutrient intake in lower-quality peat-swamp forests, where fruit masting is rare and the percentage of fruiting trees remain relatively low year-round. Thus, the ability to consume, process, and metabolize fallback foods becomes critical to maintain a steady-state of protein balance. We tested the hypothesis that during periods of fruit scarcity, orangutans have lower protein intake and lower urea concentrations, suggesting nitrogen recycling. We also examined ketone bodies in urine as evidence of ketosis. Urine samples were collected from habituated orangutans at the Tuanan Research Station in Central Kalimantan, Indonesia. We analyzed 63 urine samples from 12 individuals collected between 2009-2010.
Preliminary analyses indicated a positive relationship between urea concentration (μM urea/μM creatinine), protein availability, and protein intake (total grams/day). There was some evidence of age-class and sex differences in urea concentration for specimens sampled during the same months: independent immature males and females without offspring had lower urea concentrations. Our data suggest that Bornean orangutans in this peat swamp habitat are able to maintain a positive or neutral protein balance state by recycling nitrogen in the form of urinary urea.