Orangutan mothers adjust their behaviour during food solicitations in a way that likely facilitates feeding skill acquisition in their offspring

Immature orangutans acquire their feeding skills over several years, via social and independent learning. So far, it has remained uninvestigated to what extent orangutan mothers are actively involved in this learning process. From a fitness point of view, it may be adaptive for mothers to facilitate their offspring’s skill acquisition to make them reach nutritional independence faster. Food solicitations are potential means to social learning which, because of their interactive nature, allow to investigate the degree of active involvement of the mother. To investigate the role of food solicitation and the role of the mother in immatures’ foraging skill acquisition, we analysed 1390 food solicitation events between 21 immature Sumatran orangutans (Pongo abelii) and their mothers, collected over 13 years at the Suaq Balimbing orangutan population. We found that solicitation rates decreased with increasing age of the immatures and increased with increasing processing complexity of the food item. Mothers were more likely to share complex items and showed the highest likelihoods of sharing around the age at which immatures are learning most of their feeding skills. Our results indicate that immature Sumatran orangutans use food solicitation to acquire feeding skills. Furthermore, mothers flexibly adjust their behaviour in a way that likely facilitates their offspring’s skill acquisition. We conclude that orangutan mothers have a more active role in the skill acquisition of their offspring than previously thought.

Spatial model of human-sumatran orangutan (Pongo abelii) conflict vulnerability in Besitang, Indonesia

Sumatran orangutan is one of the key species of wildlife that live in the Besitang forest landscape. Conflicts between sumatran orangutans and humans often occur along with the narrowing of sumatran orangutan habitat. The importance of knowing the distribution of locations at risk of human-wildlife conflict is expected to be used as a reference in efforts to mitigate the occurrence of human-wildlife conflict. This study aimed to get information about the vulnerability distribution of human-sumatran orangutan conflict (HSOC) based on influenced factors in Besitang. The Principal Component Analysis (PCA) method is used to select and weight the factors that are thought to influence the distribution of HSOC. Overlay analysis of the factors influencing HSOC distribution is done using Geographic Information System (GIS). The results of the study showed that the vulnerability of HSOC could be divided into three classes namely, the highly vulnerable areas of conflict are 35,282.16 ha (21.66), medium vulnerable areas are 55,662.57 ha (34.17%) and not vulnerable areas are 71,960.85 ha (44.17%). This research will be helpful as an early warning system in HSOC mitigation efforts.

Primate selfies and anthropozoonotic diseases: lack of rule compliance and poor risk perception threatens orangutans.

Our understanding of the transmission of anthropozoonotic diseases between humans and nonhuman primates, particularly great apes due to their close genetic relationship with humans, highlights a serious potential threat to the survival of these species. This is particularly the case at tourism sites where risk of disease transmission is increased. We focus on the interaction between tourists and the Critically Endangered Sumatran orangutan (Pongo abelii) at Bukit Lawang in the Gunung Leuser National Park, Indonesia, before and after the park was closed due to the threat of Covid-19 in April 2020. Through analysis of posts on Instagram we determine the extent of compliance by visitors with the rule to keep a minimum distance of 10 meters from orangutans and assess the positional behaviours of the orangutans. Of the 2,229 photographs we assessed between November 2019 and July 2020, 279 depicted one or more orangutans. Forty-two of these contained both a human and an orangutan, and of these all showed inappropriate behaviours (direct contact, feeding orangutans, close proximity <5m) providing direct evidence of noncompliance with the 10m distance rule. Most of these photographs additionally showed orangutans performing abnormal positional behaviours such as being low to or on the ground rather than their natural high position in the canopy; being near the ground and in close proximity to humans increases the risk of anthropozoonotic disease transmission. As expected, we found a significant decrease in number of photographs that were posted following the closure, and a decrease in the proportion of photographs that showed orangutans or tourists feeding orangutans. Tourists do not seem to perceive that they pose risks to the orangutans and therefore increased awareness, education and enforcement of rules by all stakeholders, tourism bodies and government officials need to be actioned in order to safeguard this important population, which is crucial to the future survival of the Sumatran orangutan.

Nest Characteristics of the Sumatran Orangutan (Pongo abelii) in the Wildlife Sanctuary Soraya Station in Aceh Province, Indonesia

Orangutans (Pongo spp.) populations used to be widely distributed throughout Southeast Asia, from Java in the south to the Southern China in the north during the Pleistocene. Their populations have declined up to 75% of their original size and are now distributed only in parts of the tropical rainforests of Borneo and Sumatra. Pongo pygmaeus, Pongo tapanuliensis and Pongo abelii are the three most representative species, in this study, here we discussed the latter. Sumatran forests are generally suffering from deforestation with rates ranging from 3.74% to 49.85% between 2000 and 2012. Thus, human wildlife conflict intensity has escalated and gained more traction. Orangutans are known as arboreal great apes and need to build nests for resting. We applied the transect line method (three transects; each 1,000 m long) at different elevations in Soraya Research Station, Gelombang Village, Sultan Daulat sub-district, Subulussalam district, and assessed the nest characteristics. The characteristics are: (1) nesting position referring to the position of nest on a tree; (2) nest successional stages defining the age and leaf decay used in constructing a nest indicated with I (new) until V (almost gone); and (3) nest density to predict the density of nest per square km. Afterwards, the identified nesting trees along the transect were further identified based on their species, and assessed based on three characteristics (the tree height, diameter and the height of a nest measured from the soil). A total of 27 nests were found, and 44% were located in transect III or at the riparian. Out of 27, four orangutans’ nests were found on Moraceae (Streblus elongatus) and Myrtaceae (Syzigium spp.), while three nests were found on Dipterocarpus sp. The tree height, tree diameter and nest height were 10 m–25 m (mean = 17.5 m; SD = ± 0.25), 10 cm–30 cm (mean = 20 cm; SD = ± 0.4) and 16 m–20 m (mean = 18 m; SD = ± 0.35), respectively. Meanwhile, nest density calculated based on the form: d = [N/ (L* 2w)], and the values obtained were 8.4, 13.45, 26.9 nests/km2 located on transect I, II and III or at the riparian. The most commonly found nest successional stages and position were stage III and position 3, respectively. This study could serve as a baseline research in primate conservation and nest characterisation could be used as guidance for any future activity planning (e.g. tree reforestation) in a particular region and the existence of various tree species diversity are indispensable for maintaining orangutan habitats’ quality.

Vegetation structure of Sumatran Orangutan (Pongo abelii) habitat in North Sumatra, Indonesia

Zaitunah A, Samsuri, Ras S. 2021. Vegetation structure of Sumatran Orangutan (Pongo abelii) habitat in North Sumatra, Indonesia. Biodiversitas 22: 635-641. Gunung Leuser National Park forest in the Bukit Lawang section is the habitat of Sumatran Orangutan (Pongo abelii). There have been reports of the orangutans visiting the village. As some tree species are required for their sustenance to provide nests and food, there is a need to study species diversity availability in their habitat. Thus, the aim of the research was to analyze the composition and structure of the area's vegetation-this was done for the forestand mixed plantation. The sampling for the measurement of tree parameters was conducted using the line strip method. The strips (width 50 m, length 250 m) were constituted by a sub-plot measuring for seedling, pole, sapling, and trees. Within the sampling area, 181 species were found. Species within Dipterocarpaceae showed higher important value index (IVI) compared to other species in all layers. Shorea parviflora and Shorea ovalis were among the species with higher IVI in all the layers. The presence of species of Dipterocarpaceae and other species preferred by orangutans will support their quality of life. Therefore, orangutans prefer staying in the forest to entering the garden. Thus, it is concluded that their entry into the mixed gardens is related to the garden's proximity to the forest. Conservation efforts are needed to minimize the conflict between man and orangutan in the surrounding area.

Behavior Of Individual Orangutan Sumatera (Pongo Abelii) Before Direintroduction At The Orangutan Quarantine Station, Sibolangit, Deli Serdang, North Sumatera

The individual behavior of orangutan (Pongoabeli) before reintroduction to the wild was studied from March to June 2012 in orangutan quarantine station Batumbelin Sibolangit, Deli Serdang. The research used focal animal sampling method, at the same time the data recording was taken using instantenous method. The result showed that solitary behavior (39.34%) which was dominated by feeding (20.60%). The second highest (35.31%) was resting which was dominating by sitting (16.87%) followed by moving behavior (13.58%) which mostly was branching (7.54%). The least activity was competitive behavior (1.88%) which was dominated by streaking down each other (0.82%). The result also indicated an abnormal behavior among 3 orangutans observed such as eating their own feces.