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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 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
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The Context of Food Sharing and Tolerance in Wild Bornean Orangutans (Pongo pygmaeus wurmbii)
When female chimpanzees, orangutans, and callitrichids share challenging‐to‐process resources with their offspring, they improve offspring access to foods and calories which would otherwise be unavailable. Adult chimpanzees share foods rarely, but when they do, sharing valuable resources solidifies inter‐individual bonds (e.g., when building coalitions or eliciting copulations). While maternal‐offspring food sharing has been studied in wild orangutans, the context in which adult orangutans share food and feed in proximity is poorly known. We use 27 years of research on orangutans in West Kalimantan, Indonesia, to examine this behavior. Food sharing and tolerance were observed during 2,131 follows between 1994‐2019. Mother‐infant food sharing occurred in 78%, of these follows, female‐female sharing in 22%, male‐female sharing in 32%, and male‐male in just 1%. Adult females shared foods at different rates with adult males than with offspring (Chi‐square = 49.27,p< .01,N= 589 events). Eighty‐one percent of mother‐offspring food sharing/tolerance was fruit, compared to only 71% of male‐female food sharing/tolerance. Durio, Lithocarpus, and Willughbeia (hard‐to‐process fruits) were most frequently shared by mothers. Twenty‐three percent of male‐female food sharing/tolerance occurred while eating termites; only 3% of mother‐infant sharing did. Only two of 350 mouth‐to‐mouth or hand‐to‐mouth transfers involved adult males and females. Mothers increase their offspring’s access to challenging resources, while food sharing/tolerance among adult males and females is not limited to valuable resources, but may indicate strong social tolerance or affiliation in generally solitary adults
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- PAR ID:
- 10188137
- Date Published:
- Journal Name:
- 42nd Annual Meeting of the American Society of Primatologists
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Wild orangutans cope with dramatic, unpredictable fluctuations in food availability throughout development which have significant implications for energy balance for growth, development, and maintenance of body function. Foods that are especially important when preferred fruits are not available (e.g., bark/pith, termites, seeds) can require force, manual manipulation, and/or skill to access. Orangutans’ extended life history may mitigate ecological risk associated with the challenging environment of juvenile growth and development. Given the complexity of important foods, orangutans’ semi-solitary lifestyle, and the relatively brief period between weaning and independence, offspring transition to ecological independence during their extended nursing period. Here, we examine mother-offspring food transfer in the context of nutritional quality and complexity, with handling time as a proxy. Data were collected between July 2009-July 2019 in Gunung Palung National Park, Indonesia. We predict complex food items are transferred most frequently. In 245 observations of food sharing, fruit was most frequently transferred, followed by invertebrates and bark/pith. Handling time and transfer frequency were negatively correlated (Rho=-0.75, p<0.001): slower-eaten fruits were shared more frequently than rapidly-eaten fruits. Fruit size and sharing frequency were also negatively correlated (Rho=-0.73, p<0.001). There was no correlation between sharing frequency and free simple sugar concentration (Rho = 0.36, p=0.13), though sharing frequency and total nonstructural carbohydrate concentration were correlated (Rho=0.46, p=0.04). Food sharing was most common when mothers ate large, slowly-eaten fruits rich in nonstructural carbohydrates. Food sharing allows mothers to transfer more complex foods to their offspring, and may facilitate knowledge transfer as offspring become ecologically competent.more » « less
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Our previous research showed that the distance between an orangutan mother-offspring dyad decreases when males are present. This change in proximity has been argued to be one aspect of a suite of female infanticide avoidance strategies. Therefore, we hypothesized that mothers are responsible for proximity maintenance in the presence of male conspecifics. In order to investigate this hypothesis, we examined Hinde Indices and Brown-modified Hinde Indices during full day follows of mother-offspring orangutans in Gunung Palung National Park, West Kalimantan, Indonesia, from May 2018-April 2019. We found that 91% of days (N=34) had a Hinde Index indicating offspring control of proximity and 88% of days (N=34) had a Brown-modified Hinde Index indicating greater offspring responsibility for proximity changes than mother responsibility. There was no difference in the Hinde Index (Nmale absent=32, Nmale present=14, t=0.979, df=19.122, p=0.334) or Brown-modified Hinde Index (Nmale absent=32, Nmale present=14, t=0.216, df = 22.424, p=0.831) when males were present compared to when males were absent. Counter to our hypothesis, offspring, not mothers, were still responsible for proximity maintenance in the presence of males. However, controlling for variation by analyzing the data on a per follow basis, we found that Hinde Indices shifted towards becoming more mother-maintained when males were present for 70% of the follows, but this difference was not significant (N=10, t=1.050, df=9, p=0.321). One limitation in interpreting these results is that all offspring included in our study were over three years old and past the age at which they are most vulnerable to infanticide.more » « less
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Male orangutans exhibit bimaturism—two mature morphs—flanged and unflanged males. Flanged males are larger, have cheek pads (flanges) and large throat sacs, and produce long calls. Previous orangutan paternity studies found variation between the reproductive success of each morph and in the degrees of reproductive skew. However, these studies were limited by a lack of behavioral maternity data, the inclusion of ex-captive orangutans, and/or the presence of feeding stations. Here we present the first paternity data from completely wild orangutans with known mothers. We hypothesized that (1) flanged males would have higher reproductive success than unflanged males due to flanged male dominance and female preference and (2) a single male would not monopolize paternity due to the temporal and spatial distribution of fecund females. We used fecal samples collected in Gunung Palung National Park from 2008-2019 to genotype orangutans (13 offspring born 2002-2015, their 10 mothers, and 19 candidate sires) using 12 microsatellites. MICROCHECKER 2.2.3 and CERVUS 3.0 were used to confirm the suitability of the microsatellite panel, fidelity of individual identities, and genetic maternity. Paternity analysis was performed with both CERVUS 3.0 and COLONY 2.0.6.7. We were able to identify paternity for six offspring. Four flanged males sired five offspring, and one sire’s morph was unknown at the time of conception. We found that flanged males have higher reproductive success and that females are not monopolizable in this completely wild setting. We discuss the implications of all published orangutan paternity results for understanding bimaturism in orangutans.more » « less
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null (Ed.)Abstract Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these differences develop in immatures. We analyzed 11 years of feeding data on ten adult female, seven flanged male, and 14 immature Bornean orangutans ( Pongo pygmaeus wurmbii ) at Tuanan in Central Kalimantan, Indonesia. We found that the diets of the adult females were significantly broader and required more processing steps before ingestion than the diets of flanged males. We also found evidence for a similar difference in overall diet repertoire sizes. For the immatures, we found that whereas females reached 100% of their mothers’ diet spectrum size by the age of weaning, males reached only around 80%. From the age of 4 years on (i.e., years before being weaned) females had significantly broader daily diets than males. We found no difference in daily or overall diet processing intensity of immature males and females but found preliminary evidence that immature males included fewer items of their mother’s diet in their own diets that were processing-intensive. Overall, our results suggest that by eating a broader variety and more complex to process food items, female orangutans go to greater lengths to achieve a balanced diet than males do. These behavioral differences are not just apparent in adult foraging behavior but also reflected in immature development from an early age on. Significance Statement In many species, males and females have different nutritional needs and are thus expected to show sex-specific foraging behavior. Sex differences in several aspects of foraging behavior have been found in various species, but it remains largely unclear when and how those develop during ontogeny, which is especially relevant for long-lived altricial species that learn foraging skills over many years. In our study, we analyzed a cross-sectional and longitudinal data set containing more than 750,000 feeding events of adult and immature Bornean orangutans ( Pongo pygmaeus wurmbii ). We found that adult females had significantly broader and more complex diets than males. We also found that these differences started to develop during infancy, suggesting that immature orangutans prepare for their sex-specific foraging niches long before those become physiologically relevant while they are still in constant association with their mothers and before being frequently exposed to other role models.more » « less
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