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.
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What’s for dinner? Diurnal variation in wild Bornean orangutan food and nutrient choices
Previous observational research on primate feeding ecology has demonstrated that some primates consume fruit in the morning and leaves in the afternoon. However, diurnal patterning of feeding bouts has not been demonstrated for many of the apes, nor for relatively solitary primates. Furthermore, whether this has nutritional consequences is unclear. Orangutans are largely frugivorous omnivores that also incorporate leaves, bark, pith, and insects in their diet. As primarily solitary animals, their foraging and food choices are not restricted by group size and group decisions – thus they provide an excellent species with which to examine individual ape foraging choices. In accord with previous research, we hypothesized that orangutans would select energy rich and easy to digest foods (i.e., fruit) in the morning, then move to leaves and more fibrous food sources later in the day in order to allow more digestion time, and possibly to gain necessary macronutrients at the optimal time. We examined whether orangutans exhibited diurnal patterning of feeding bouts using 51 full day follows of wild Bornean orangutans (Pongo pygmaeus wurmbii) occurring May 2015 – January 2016 at Gunung Palung National Park, West Kalimantan, Indonesia. While there is a statistically significant difference in food types eaten at different times of day (χ2 = 76.3, p = 0.03), this difference is driven by increased consumption of leaves and pith in the afternoon hours, while fruit is consistently consumed throughout the day. We discuss this in the contexts of optimal nutrient selection and the Geometric Framework of Nutrition.
Funding: National Science Foundation (BCS-1638823; BCS-1613393), NSF GRFP (DGE-1247312); Boston University; National Geographic Society, US Fish and Wildlife (F15AP00812), Leakey Foundation, Disney Wildlife Conservation Fund; Wenner-Gren Foundation; Nacey-Maggioncalda Foundation
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- Award ID(s):
- 1638823
- NSF-PAR ID:
- 10067611
- Date Published:
- Journal Name:
- 87th Annual Meeting of the American Association of Physical Anthropologists
- Page Range / eLocation ID:
- 68
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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