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Monitoring health status is a critical aspect of primate conservation, yet can be difficult to noninvasively investigate in the wild. Because mammals are endothermic, body temperature can be used as a health marker for primates. Using a method previously tested on chimpanzees and humans, we estimated body temperature of wild Bornean orangutans by measuring the internal temperature of fecal samples. Upon quickly collecting a fecal sample after defecation, we recorded internal temperature of the sample at 20-sec intervals for six minutes. Data included a series of temperatures for each sample that we fitted to a sigmoid curve, which was used to estimate body temperature. Estimated body temperature was not affected by sex (F(2,92)= 0.431, P= 0.651), weather (F(2,92)= 1.175, P= 0.313), or collection time (r= -0.074, N= 95, P= 0.468). Estimated body temperature was higher for fecal samples that fell from lower estimated heights (r= -0.23, N= 95, P= 0.0004) and were heavier (r= 0.23, N= 75, P= 0.0475). We compare these results from the field to captive fecal samples, taking place on the ground, to determine the accuracy of this field method. From our field samples (N=95), orangutans appear to have a lower internal body temperature (33.44 ± 1.74 °C) on average than either chimpanzees or humans. Previous studies have demonstrated that orangutans have a lower metabolic rate than other great apes. Lower body temperature may serve as a metabolic adaptation of orangutans to survive extended periods of low food availability when energy needs to be conserved. 

Primate health status affects individual fitness and survival, yet is difficult to noninvasively investigate in the wild. Using a method tested on chimpanzees and humans, we estimated temperature of fecal samples of Bornean orangutans as a proxy for body temperature. Upon defecation, we recorded peak internal temperature of the samples. Estimated body temperature was influenced by height of defecation (r= -0.23, N= 95, P= 0.0004) and sample weight (r= 0.23, N= 75, P= 0.0475). These estimates were not affected by sex (F(2,92)= 0.431, P= 0.651) or weather (F(2,92)= 1.175, P= 0.313). Our method allowed for fast, consistent sampling, such that time from defecation to collection did not affect the results (r= -0.074, N= 95, P= 0.468), confirming reliable fecal temperatures can be collected from orangutans. We compare our results from the field to captive fecal samples, finding higher body temperatures in captivity. From our samples (N=95), orangutans appear to have a lower internal body temperature (33.44 ± 1.74 °C) on average than either chimpanzees or humans. Previous studies have demonstrated that orangutans have a lower metabolic rate than other great apes. Lower body temperature may serve as a metabolic adaptation of orangutans to survive extended periods of low food availability when energy must be conserved. 

Infanticide as a male reproductive tactic is widespread across mammals, and is particularly prevalent in catarrhine primates. While it has never been observed in wild orangutans, infanticide by non-sire males has been predicted to occur due to their extremely long inter-birth intervals, semi-solitary social structure, and the presence of female counter-tactics to infanticide. Here, we report on the disappearance of a healthy four-month-old infant, along with a serious foot injury suffered by the primiparous mother. No other cases of infant mortality have been observed at this site in 30 years of study. Using photographic measurements of the injury, and information on the behavior and bite size of potential predators, we evaluate the possible causes of this injury. The context, including the behavior of the female and the presence of a new male at the time of the injury, lead us to conclude that the most likely cause of the infant loss and maternal injury was male infanticide. We suggest that in orangutans, and other species where nulliparous females are not preferred mates, these females may be less successful at using paternity confusion as an infanticide avoidance tactic, thus increasing the likelihood of infanticide of their first-born infants. 

The Gunung Palung Orangutan Project has conducted research on critically endangered wild Bornean orangutans (Pongo pygmaeus wurmbii) since 1994 in Gunung Palung National Park, West Kalimantan, Indonesia. A major goal of our broad-ranging research on orangutan behavior and ecology is to understand how the unique rainforest environment of Southeast Asia, characterized by dramatic changes in fruit productivity due to unpredictable mast fruiting, impacts orangutan behavior, physiology, and health. Much of our research has been devoted to the development of non-invasive techniques and an integrated biology approach – using hormonal assays, fecal processing, nutritional analysis, genetics, and behavioral ecology – and has led to an increased understanding of the ecological and evolutionary pressures shaping orangutan adaptations. Our results show that the extended life history and very slow reproductive rate of orangutans are adaptations to their environment. Orangutans in the Gunung Palung landscape, as elsewhere across Borneo and Sumatra, also face a series of conservation challenges, including extensive habitat loss and the illegal pet trade. We highlight how our investigations of orangutan health status, ecosystem requirements, and the assessment of orangutan density using ground and drone nest surveys have been applied to conservation efforts. We describe our project’s direct conservation interventions of public education and awareness campaigns, sustainable livelihood development, establishment of village-run customary forests, investigation of the illegal pet trade, and active engagement with Indonesian government organizations. These efforts, in concert with the development of local scientific and conservation capacity, provide a strong foundation for further conservation as orangutans face a challenging future.