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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. 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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3. 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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4. Behavioral Evidence of Wild Bornean Orangutans Navigating to Non-Fruit Foods – Implications for Fallback Foods

   DiGiorgio, AL; Susanto, TW; Knott, CD (January 2020, 6th Annual Meeting of the North Eastern Evolutionary Primatologists)

   null (Ed.)

   In 2015, Lambert and Rothman urged primate nutritional ecologists to revise the view of fallback and optimal foods from stable traits inherent in the food to variable qualities determined by the state of the consumer. Here we provide behavioral evidence to support this revision. In primates, fruit is often the preferred food category because it is typically high-energy, high-carbohydrate, and low in fiber. Orangutans in particular, are said to consume fruit preferentially and when it is available, whereas leaves, bark, and pith are often considered fallback foods. Using movement ecology, we ask if wild Bornean orangutans (Pongo pygmaeus wurmbii) navigate only to fruit, or whether navigation to non-fruit foods is supported by our data. We find that orangutans do deviate from a direct fruit-to-fruit path to consume non-fruit foods (n = 54, range 8% - 84%; p = 6.819e-07.) Next, we ask if orangutans consume non-fruit foods when in the proximity of fruit resources. We find that 25.5% of the time that orangutans eat a non-fruit food, there is an available fruit within 50m (n=308). Building on previous research finding that orangutans maintain a 10.1:1 NPE:P balance, we use this geospatial data showing that orangutans navigate to and choose non-fruit foods, even when fruit is available, to suggest that orangutans are seeking foods based on their current nutritional state and not only to maximize energy. This supports the claim that 'fallback' is not an inherent characteristic of a food, but rather is in the state-dependent eye of the consumer. Funders: 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, Princeton University 

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5. Behavioral Evidence of Wild Bornean Orangutans Navigating to Non-Fruit Foods – Implications for Fallback Foods

   DiGiorgio, AL; Susanto, TW; Knott, CD (January 2021, American journal of physical anthropology)

   null (Ed.)

   In 2015, Lambert and Rothman urged primate nutritional ecologists to revise the view of fallback and optimal foods from stable traits inherent in the food to variable qualities determined by the state of the consumer. Here we provide behavioral evidence to support this revision. In primates, fruit is often the preferred food category because it is typically high-energy, high-carbohydrate, and low in fiber. Orangutans in particular, are said to consume fruit preferentially and when it is available, whereas leaves, bark, and pith are often considered fallback foods. Using movement ecology, we ask if wild Bornean orangutans (Pongo pygmaeus wurmbii) navigate only to fruit, or whether navigation to non-fruit foods is supported by our data. We find that orangutans do deviate from a direct fruit-to-fruit path to consume non-fruit foods (n = 54, range 8% - 84%; p = 6.819e-07.) Next, we ask if orangutans consume non-fruit foods when in the proximity of fruit resources. We find that 25.5% of the time that orangutans eat a non-fruit food, there is an available fruit within 50m (n=308). Building on previous research finding that orangutans maintain a 10.1:1 NPE:P balance, we use this geospatial data showing that orangutans navigate to and choose non-fruit foods, even when fruit is available, to suggest that orangutans are seeking foods based on their current nutritional state and not only to maximize energy. This supports the claim that 'fallback' is not an inherent characteristic of a food, but rather is in the state-dependent eye of the consumer. Funders: 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, Princeton University 

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