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Title: Ingestive Behavior of Bornean Orangutans (Pongo pygmaeus wurmbii): coping with mechanical challenges while foraging

Bornean orangutans (Pongo pygmaeus wurmbii) preferentially eat pulp and mesocarp when fleshy fruit is abundant. However, during non-masting periods, orangutans rely on foods that can be mechanically challenging, including leaves, woody plant tissue, and seeds. Although adult orangutans’ jaws are well adapted for intense and, perhaps, repetitive loading during chewing, it may be easier for flanged adult males to process tough or hard foods than for adult females because of dramatic sexual dimorphism. Here, we use video data and in situ focalobservations from Gunung Palung National Park, West Kalimantan, Indonesia to test the hypotheses that orangutans exhibit food- and sex-specific oral processing profiles. Pilot data (n=94 feeding bouts; 76 adult females, 18 adult males) suggest no significant differences in use of incisors (F(3,71)=0.41, p=0.75), canines (F(3,71)=0.78, p=0.52), or molars (F(3,71)=0.88, p=0.46) per ingestive action while processing fruit, leaves, termites, or bark. Females used significantly more incisions per ingestive action (2.20) than males (1.01) (t=2.44, p=0.008), and, though differences were not significant, performed more canine bites (female mean=0.08, male mean=0.00, p=0.17) and mastications (female mean=4.88, male mean=3.95, p=0.24) per ingestive action than males. We detected no difference in the behaviors used by orangutans to process different food types, despite great variation in food mechanical properties. However, this may be because our pilot data did not capture the range of mechanical challenges in orangutan diets. Nevertheless, our preliminary results support the hypothesis that adult females work harder than more » flanged males during oral food processing, explicable due to sexual dimorphism. National Science Foundation (BCS-1638823, BCS-0936199); National Geographic Society; US Fish and Wildlife (F15AP00812, F12AP00369, 98210-8- G661); Leakey Foundation; Disney Wildlife Conservation Fund; Wenner-Gren Foundation; Nacey-Maggioncalda Foundation « less
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87th Annual Meeting of the American Association of Physical Anthropologists
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National Science Foundation