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1. The Context of Food Sharing and Tolerance in Wild Bornean Orangutans (Pongo pygmaeus wurmbii)

   Kane, Erin E; Susanto, Tri Wahyu; Knott, Cheryl D (August 2020, 42nd Annual Meeting of the American Society of Primatologists)

   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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2. Developmental tradeoffs: Fruit availability and offspring age influence mother and offspring activity in Bornean orangutans (Pongo pygmaeus wurmbii)

   Kane, EE; Susanto, TW; Knott, CD (January 2021, American journal of physical anthropology)

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   Bornean orangutans' extended life history may be an adaptation to their forest habitat, characterized by dramatically fluctuating fruit availability. We hypothesize that juveniles rest and are carried more when fruit availability is low, spending less time in developmentally important behavior including play and independent travel to conserve energy. We test this using generalized linear mixed models and data derived from 976 follows of infant and juvenile orangutans collected during periods of varying fruit availability. Age (p<0.001), but not fruit availability (p>0.05) significantly affected offsprings’ time being carried (β=-8,1) and resting (β=-2.6, p<0.001). Younger individuals spent more time clinging and resting regardless of fruit availability. Fruit availability and offspring age interact to affect the proportion of time juveniles play (β=1.5, p<0.001) and travel (β=-0.8, p<0.001). Fruit availability impacts younger juveniles’ play behavior more dramatically than older juveniles: younger juveniles play more when fruit availability is high than when it is low, while older juveniles exhibit little variation in time spent playing depending on fruit availability. Juveniles aged 6-8 travel more when fruit availability is medium and high, juveniles aged 2-5 travel slightly less when fruit availability is high, and juveniles under 2 rarely travel independently. We also examined relationships between fruit availability, offspring age, and maternal travel distance using 2065 mother-offspring follows, demonstrating that females travel shorter distances with offspring under four, and when fruit availability is low. Thus, orangutans shift activity in response to fruit availability and throughout development, buffering young orangutans against energy depletion but suppressing developmentally important activities. Funders: NSF (9414388, BCS-1638823, BCS-0936199); National Geographic; USFish/Wildlife (F18AP00898, F15AP00812, F13AP00920, 96200-0-G249, 96200-9-G110); Leakey; Disney Conservation Fund; Wenner-Gren; Nacey-Maggioncalda; Conservation-Food-Health; Orangutan Conservancy; Woodland Park Zoo 

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3. Foraging efficiency and ecological risk aversion in juvenile Bornean orangutans; Program of the 86th Annual Meeting of the American Association of Physical Anthropologists

   https://doi.org/10.1002/ajpa.23210  

   Knott, Cheryl; DeLong, K (April 2017, American Journal of Physical Anthropology)

   For species with low mortality and high reproductive costs, like primates, rather than maximize reproduction, natural selection should favor slow growth and slow reproductive rates. Orangutans, because of their slow life history, and the extreme fluctuations in their food supply, are hypothesized to have been selected for slow juvenile development to avoid ecological risk. Juveniles are predicted to be particularly vulnerable during periods of low food availability because of lower foraging success. Thus, we tested the hypothesis that juvenile orangutans are less efficient foragers than adults and that they are less able to both access and digest important fall-back foods. Data were collected on wild orangutans in Gunung Palung National Park, Borneo, Indonesia between 1994-2016. Analyses are drawn from 468 matched follows of mother-offspring pairs in which more than 75% of the diet has been analyzed. We found that juveniles ate fruit when their mother’s ate fruit during 98.3% of bouts. However, for other food items, juveniles were much less likely to eat the same food items (insects = 65.2%, leaves 76.5, bark 70.0%, flowers 75.0%, pith 65.8%). As expected, we found that juveniles ate significantly fewer calories than did adults overall, but this difference was particularly pronounced during periods of low food availability (p < 0.001). We show that these results were due to constraints on both the processing and digesting of fall-back foods. Thus, the long period of orangutan growth and dependency may reflect a risk-averse growth strategy in this forest characterized by dramatic fluctuations in preferred fruits. 

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4. Foraging efficiency and ecological risk aversion in juvenile Bornean orangutans

   Knott, Cheryl; DeLong, K (January 2017, American Association of Physical Anthropologists Annual Meeting)

   For species with low mortality and high reproductive costs, like primates, rather than maximize reproduction, natural selection should favor slow growth and slow reproductive rates. Orangutans, because of their slow life history, and the extreme fluctuations in their food supply, are hypothesized to have been selected for slow juvenile development to avoid ecological risk. Juveniles are predicted to be particularly vulnerable during periods of low food availability because of lower foraging success. Thus, we tested the hypothesis that juvenile orangutans are less efficient foragers than adults and that they are less able to both access and digest important fall-back foods. Data were collected on wild orangutans in Gunung Palung National Park, Borneo, Indonesia between 1994-2016. Analyses are drawn from 468 matched follows of mother-offspring pairs in which more than 75% of the diet has been analyzed. We found that juveniles ate fruit when their mother’s ate fruit during 98.3% of bouts. However, for other food items, juveniles were much less likely to eat the same food items (insects = 65.2%, leaves 76.5, bark 70.0%, flowers 75.0%, pith 65.8%). As expected, we found that juveniles ate significantly fewer calories than did adults overall, but this difference was particularly pronounced during periods of low food availability (p < 0.001). We show that these results were due to constraints on both the processing and digesting of fall-back foods. Thus, the long period of orangutan growth and dependency may reflect a risk-averse growth strategy in this forest characterized by dramatic fluctuations in preferred fruits. 

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5. Ecological competence in wild Bornean orangutans: food sharing, processing, and nutrition

   Kane, Erin E; Susanto, Tri Wahyu; Conklin-Brittain, Nancy L; Knott, Cheryl D (October 2019, Third Lembersky Conference in Human Evolutionary Studies)

   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. 

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