Search for: All records

Orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, West Kalimantan, Indonesia experience significant seasonal and annual fluctuations in the availability of their preferred food, ripe fruit. When ripe fruit is limited, orangutans increase their consumption of bark, pith, and leaves, which are continuously available and may act as fallback foods. While these foods are presumed to be less nutritious, it is not clear whether this is the case. Free simple sugars (FSS) provide orangutans with readily-metabolizable energy, and are thus an important nutritional compound for food choice. Here, we examine FSS concentrations in a variety of orangutan foods (n=54) to better understand orangutan foraging and nutritional ecology. We predicted that preferred foods would have higher concentrations of FSS than fallback foods. We analyzed FSS concentrations using a modified phenol-sulfuric acid method, and tested sample absorbency using a spectrophotometer at 490 nm. We analyzed 54 samples from 48 species, examining six plant parts: bark, flowers, leaves, pulp, seeds, and skin/pulp. Although preliminary results indicated no statistically significant differences in sugar content across the six food categories (F(5,47)=1.78, p=0.14), we did find that preferred foods (fruit pulp and seeds) had an average sugar concentration that was significantly higher (4.7%) than fallback foods (leaves and bark) (t=2.355, p=0.04). Therefore, as predicted, we find that orangutans prefer food types with higher concentrations of FSS. Obtaining adequate caloric and nutritional intake is crucial for orangutan reproduction and development, and thus this study provides new insight into what drives orangutan dietary choices. National Science Foundation (BCS-1638823, BCS-0936199, 9414388), National Geographic Society, US Fish and Wildlife (F15AP00812, F12AP00369, 98210-8-G661), Leakey Foundation, Disney Wildlife Conservation Fund, Wenner-Gren Foundation, Nacey- Maggioncalda Foundation.