After the smoke has cleared: Extended low fruit productivity following forest fires decreased gregariousness and social tolerance among wild female Bornean orangutans (Pongo pygmaeus wurmbii)

As climate change continues to fundamentally alter resource landscapes, the ability to flexibly respond to spatio-temporal changes in the distribution of preferred food sources is increasingly important for the overall health and fitness of animals living in seasonal, variable, and/or changing environments. Here, we investigate the effects of an uncharacteristically long period of fruit scarcity, following widespread thick haze caused by peat and forest fires in 2015, on the behaviour and sociality of female Bornean orangutans (Pongo pygmaeus wurmbii). We collected data from 2010 to 2018 at Tuanan, Central Kalimantan, Indonesia, and compared the activity, diet, and association patterns of adult females during low-fruit periods before the fires, i.e., regular, seasonal periods of low fruit availability (“pre-fire”), and after the fires, i.e., during the extended period of low fruit availability (“post-fire”). First, we found that, post-fire, female orangutans adopted a more extreme energy-saving activity pattern and diet — resting more, travelling less, and diet-switching to less-preferred foods — compared to pre-fire. Second, we found that the probabilities of association between females and their weaned immature offspring, and between related and unrelated adult females were lower, and the probability of agonism between unrelated females was higher, post-fire than pre-fire. This change in energetic strategy, and the general reduction in gregariousness and social tolerance, demonstrates how forest fires can have lasting consequences for orangutans. Fission–fusion species such as orangutans can mitigate the effects of changes in resource landscapes by altering their (sub)grouping patterns; however, this may have long-term indirect consequences on their fitness.

The development and maintenance of sex differences in dietary breadth and complexity in Bornean orangutans

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.

Model spasial distribusi habitat orangutan kalimantan (Pongo pygmaeus wurmbii) menggunakan logistik regresi di DAS Katingan

DAS Katingan merupakan salah satu habitat Orangutan Kalimantan (Pongo pygmaeus wrumbii) yang saat ini berstatus Critically Endangered (IUCN 2016), dilindungi oleh peraturan pemerintah Indonesia (P.106 / 2018), dan termasuk dalam Apendiks 1 (CITES 2017). Kondisi habitat Orangutan Borneo semakin terancam oleh perubahan tutupan lahan. Pengelolaan habitat diperlukan untuk melindungi populasi Orangutan Kalimantan. Tujuan dari penelitian ini adalah membuat model distribusi habitat orangutan kalimantan di DAS Katingan serta memberikan rekomendasi manajemen habitatnya. Model kesesuaian habitat Orangutan Kalimantan menggunakan metode regresi logistik mendapatkan lima variabel lingkungan yang meliputi ketinggian, jarak dari situs budaya, jarak dari jalan, jarak dari pemukiman, dan NDVI. Tes Hosmer-Lemeshow menunjukkan nilai kelayakan sebesar 0.481 dengan Nagelker R2 = 0.866, dan validasi Kappa Accuracy 77%. Total kesesuaian habitat Orangutan Kalimantan di DAS Katingan adalah 1,250,174.35 ha (64.11% dari luas DAS Katingan). Habitat utama Orangutan Borneo teridentifikasi di Taman Nasional (TN), Hutan Lindung (HL), dan Kawasan Suaka Alam/Kawasan Pelestarian Alam (KSA/KPA) dengan luas 395,178.30 ha (31,66% dari total luas habitat). Habitat terisolasi yang diidentifikasi di timur laut DAS Katingan. Manajemen habitat dapat dilakukan dengan membuat koridor dengan lebar minimum 500 meter di areal berhutan.

The cost of associating with males for Bornean and Sumatran female orangutans: a hidden form of sexual conflict?

Sexual coercion, in the form of forced copulations, is relatively frequently observed in orangutans and generally attributed to their semi-solitary lifestyle. High ecological costs of association for females may be responsible for this lifestyle and may have prevented the evolution of morphological fertility indicators (e.g., sexual swellings), which would attract (male) associates. Therefore, sexual conflict may arise not only about mating per se but also about associations, because males may benefit from associations with females to monitor their reproductive state and attempt to monopolize their sexual activities. Here, we evaluate association patterns and costs for females when associating with both males and females of two different orangutan species at two study sites: Suaq, Sumatra (Pongo abelii), and Tuanan, Borneo (Pongo pygmaeus wurmbii). Female association frequency with both males and females was higher in the Sumatran population, living in more productive habitat. Accordingly, we found that the cost of association, in terms of reduced feeding to moving ratio and increased time being active, is higher in the less sociable Bornean population. Males generally initiated and maintained such costly associations with females, and prolonged associations with males led to increased female fecal cortisol metabolite (FCM) levels at Tuanan, the Bornean population. We conclude that male-maintained associations are an expression of sexual conflict in orangutans, at least at Tuanan. For females, this cost of association may be responsible for the lack of sexual signaling, while needing to confuse paternity. Significance statement Socioecological theory predicts a trade-off between the benefits of sociality and the ecological costs of increased feeding competition. Orangutans’ semi-solitary lifestyle has been attributed to the combination of high association costs and low predation risk. Previous work revealed a positive correlation between association frequencies and habitat productivity, but did not measure the costs of association. In this comparative study, we show that females likely incur costs from involuntary, male-maintained associations, especially when they last for several days and particularly in the population characterized by lower association frequencies. Association maintenance therefore qualifies as another expression of sexual conflict in orangutans, and especially prolonged, male-maintained associations may qualify as an indirect form of sexual coercion.

Dinamika Perilaku Orangutan Kalimantan (Pongo pygmaeus wurmbii) di Taman Nasional Sebangau Kalimantan Tengah

Sebangau National Park represents a relatively intact peatland ecosystem and is one of the pockets of the P.p. ssp. wurmbii crucial in the world. Anthropological studies state that Orangutans have a social unit in a complex structure. The logical consequence of this condition is that many observed behaviors attract and open up new knowledge related to space use patterns. This study aims to uncover the dynamics of orangutan behavior by presenting critical evidence. This research is a descriptive exploratory study, using a non-invasive observation method with a camera trap approach, in the Punggualas area, from January 2012 to January 2014. The results show confirmation of walking on the forest floor as a new part of the orangutan association of behavior. Based on this, the conclusion drawn is that the dynamics of orangutan behavior develop dynamically in response to changes in natural habitat conditions.

ANALISIS KANDUNGAN AIR SUMBER PAKAN ORANGUTAN KALIMANTAN (Pongo pygmaeus wurmbii) DI STASIUN RISET CABANG PANTI TAMAN NASIONAL GUNUNG PALUNG KALIMANTAN BARAT

Water is a very important nutrient for primate health, as it serves as a medium facilitating chemical reactions in the body. The abundance of food sources in forests is one of the things keeping orangutans from extinction. Therefore, it is important to know the proportion of water in the food of orangutans in the forest, their natural environment. Our goal was to define the content of water in the diet of Bornean Orangutan (Pongo pygmaeus wurmbii). The method used in this study is gravimetry, an analysis method based on weight measurements involving the formation, isolation and measurement of the weight of a food ingredient. Results showed the highest water content in the fruits of genus Gironniera 93,634%, and the lowest in the fruits of genus Ficus 38,771%. Based on age and gender, the percentage of consumption of feed water content in orangutans shows that there are differences.Keywords: Analysis of water content, feed, orangutans

PEMANFAATAN RUANG VERTIKAL PADA AKTIVITAS HARIAN ORANGUTAN (Pongo pygmaeus wurmbii) DI STASIUN RISET CABANG PANTI TAMAN NASIONAL GUNUNG PALUNG, KALIMANTAN BARAT

Orangutans are solitary animals from the Pongidae family. There are three sub-species of Bornean orangutans, i.e. Pongo pygmaeus wurmbii, P. pygmaeus pygmaeus and P. pygmaeus morio, all of which are highly endangered. Orangutans carry out several daily activities such as eating, moving, resting, and nesting in the tree canopy. However, it has yet remains unknown on how their behaviours vary with tree height. This study aimed to determine the frequency of presence, daily activities of orangutans, and vertical space utilization in orangutan activities in the natural habitat of the Panti Branch Research Station, Gunung Palung National Park. This study used the Focal Animal Sampling method with a two minute time interval for ± 12 hours and was studied for over six months. The focal orangutans whose activities were recorded during the study consisted of 12 individuals divided into 3 age groups, namely the adult, adolescent, and juvenile age groups. The results showed that the daily activity of orangutan was observed on 36 species of trees with the greatest frequency found on Garcinia sp. and Syzigium sp. accounted for33% each. The female orangutans were found to be more dominant in feeding activities (3.93 per day), while male orangutans spent more time for resting activities (4.56 hours per day). The utilization of vertical space in young male orangutans took place in tall trees and eating activities occurred at an altitude of 33.6 m. On average, teenage female orangutans choose tree to make their nests in trees 30 m high.