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1. The Response of Orangutans to a Total Solar Eclipse Event

   Prasetyo, D. (April 2021, Journal of Tropical Biodiversity)

   Mitra Setia, Tatang (Ed.)

   A complete solar eclipse is a rare event, and we know very little about how other species, including our closest living relatives the primates, react to these events. We observed orangutans on the island of Borneo, Indonesia during a rare astronomical event of a total solar eclipse. Captive orangutans in Nyarumenteng rehabilitation center, Central Kalimantan were observed to document their reaction to this unexpected environmental event. Based on this study that was conducted in 2016, the dramatical behavior demonstrated in the time of the total solar eclipse, and the general response differed between before and after the event. During the total solar eclipse, flanged males tended to increase their social behavior compared to the unflanged males. These findings indicate that the total solar eclipse resulted in an environmental stressor for these captive orangutans. 

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2. The response of orangutans to a total solar eclipse event

   Prasetyo, D. (April 2021, Journal of Tropical Biodiversity)

   null (Ed.)

   A complete solar eclipse is a rare event, and we know very little about how other species, including our closest living relatives the primates, react to these events. We observed orangutans on the island of Borneo, Indonesia during a rare astronomical event of a total solar eclipse. Captive orangutans in Nyarumenteng rehabilitation center, Central Kalimantan were observed to document their reaction to this unexpected environmental event. Based on this study that was conducted in 2016, the dramatical behavior demonstrated in the time of the total solar eclipse, and the general response differed between before and after the event. During the total solar eclipse, flanged males tended to increase their social behavior compared to the unflanged males. These findings indicate that the total solar eclipse resulted in an environmental stressor for these captive orangutans. 

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3. Wild Bornean orangutans (Pongo pygmaeus wurmbii) navigate to non-fruit foods

   DiGiorgio, Andrea D.; Susanto, Tri Wahyu; Knott, Cheryl D. (February 2020, American journal of physical anthropology)

   Wild primates have foraging goals beyond energy maximization. These foraging goals are often met by less energy dense, and more reliable, non-fruit foods. Are they able to meet these goals by navigating to high-energy fruit resources and consuming non-fruit (lower-energy) foods along the way, or do they navigate to non-fruit foods as well? Here we address this question in wild Bornean orangutans, a species known for consuming ripe fruit when it is available. Our research suggests that orangutans maintain a ratio of non-protein energy to protein and choose to consume non-fruit foods when in proximity to fruit foods. Using the movement ecology paradigm, we examine sequences of feeding bouts where an orangutan travels from one fruit patch to another, stopping at one or two non-fruit foods along the way (n = 54). By asking whether the direct path length between the two fruit patches is the same as, or less than, the actual travelled path length, we can determine whether the orangutans deviate from a fruit-to-fruit path and navigate to non-fruit foods. We find that orangutans do deviate from the direct fruit-to-fruit path by an average additional 18% of path length (range 8% - 84%; p = 6.819e-07). This is not impacted by fruit availability. This research suggests that orangutans are navigating to more constant non-fruit foods as well as the temporally and spatially patchy fruit resources. We discuss this in terms of which types of foods orangutans are navigating toward. 

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4. Rhesus monkeys show greater habituation to repeated computer-generated images than do orangutans

   https://doi.org/10.1016/j.beproc.2024.105011  

   Webster, Mackenzie F.; Engelberg, Jonathan W.M.; Hampton, Robert R. (March 2024, Behavioural Processes)
5. Home Range Overlap in Female Bornean Orangutans: Responses to Fluctuations in Food Availability

   Zdanowicz, V; Blackburn, A; Susanto, TW; Knott, CD (January 2020, 6th Annual Meeting of the Northeastern Evolutionary Primatologists)

   null (Ed.)

   Bornean orangutans (Pongo pygmaeus wurmbii) are large bodied great apes that live in rainforests dominated by mast-fruiting dipterocarp trees with extreme fluctuations in fruit availability. Orangutans respond to this temporal and spatial variability in fruit production by ranging over large areas and adopting a semi-solitary social structure. Females have overlapping home ranges, engage in both scramble and contest competition for food, and actively avoid each other. Overlap requires individuals to share access to resources and adjust ranging to optimize energy intake, thus habitat quality likely influences ranging patterns. Here we investigate whether habitat and food availability are significant predictors of female orangutan home range overlap using data collected at Gunung Palung National Park, Indonesia, a site with 7 distinct habitats. Researchers collected GPS waypoints of orangutan movements during all day focal follows. Fruit availability was measured through monthly monitoring of over 6000 trees, across 60 plots. We used R to calculate range overlap per habitat between pairs of adult female orangutans over three-month periods (2013-2019). Our results show a trend towards a negative relationship between overlap and fruit availability (N=15, Pearson’s R= -0.322, p=0.242). We also found habitat to be a predictor of female range overlap, with overlap most likely to occur in the alluvial bench habitat and significantly less likely in the peat swamp (p<0.05). These findings reveal the independent influences of fruit availability and habitat type on female orangutan home range overlap, highlighting the potential importance of habitat-specific food availability on ranging behavior and contest competition. 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; Boston University GRAF 

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