Orangutan Research Articles

Successful observation of orangutans in the wild with thermal-equipped drones

We investigated the efficacy of a drone equipped with a thermal camera as a potential survey tool to detect wild Bornean orangutans (Pongo pygmaeus) and other tropical primates. Using the thermal camera we successfully detected 41 orangutans and a troop of proboscis monkeys, all of which were confirmed by ground observers. We discuss the potential advantages and limitations of thermal-equipped drones as a tool to complement other methods, and the potential of this technology for use as a future survey tool.

IDENTIFIKASI JENIS POHON SARANG DAN PAKAN ORANGUTAN (Pongo pygmaeus) DI ARBORETUM NYARU MENTENG, PALANGKA RAYA (Identification of Trees as Nest and Food of Orangutan (Pongo pygmaeus) at the Arboretum of Nyaru Menteng, Palangka Raya)

ABSTRACT This research was aimed to know some trees that used to nest and food of orang utan (Pongo pygmaeus) at the arboretum of Nyaru Menteng in Palangka Raya City. Analysis of vegetation using Point Centered Quarter Method with 23 sample points at the field. Collected data at the August 2017 were founded 25 species of trees, from16 family, whereas 17 trees were used as nest and food and 8 trees were used as nest only. The distance between each tree to measuring point was 3,71 m. Density of the trees namely 726 trees ha-1, with domination namely 28.37, frequency namely 3.48. The important value index of hangkang (Palaquium leiocarpum) was highest, namely 51.91%. Summed dominance ratio namely 17.3 %. Diversity index was moderate with value namely 2.81. Evenness index was high with value namely 0.87.
 Keywords: Food, nest, Nyaru Menteng, Pongo pygmaeus

KEPADATAN POPULASI DAN JENIS PAKAN KELASI (Presbytis rubicunda Muller 1838) DI KAWASAN ARBORETUM NYARU MENTENG, PALANGKA RAYA

ABSTRACK Nyaru Menteng arboretum is the genetics resources area that located at the Palangka Raya District, its wide namely 65.2 ha. In this area, there are many flora and fauna, including kelasi (Presbytis rubicunda), a species in danger that protected by law. At the Nyaru Menteng arboretum area, there are also the Re- introduction of Orang Utan Centre that managed by BOS. This research was aimed to know the kelasi population at the Nyaru Menteng arboretum area and to record some herbs and plants to be their foods. The research was conducted at the Nyaru Menteng arboretum area at 2017 using survey method to calculate the population of kelasi number and wide of their habitat. Research result showed that there one kelasi at January 2017 at three kelasi at April 2017 namely kelasi of male, female and young. Analysis result showed that the density of kelasi was 0.06 species ha-1. There is decrement kelasi at 2017 than 2007. Ten years ago, kelasi was detectabled namely 15 species with the density was 0.23 species ha-1. Some herbs and plants which to be food of kelasi i.e. jambuan (Syzgium cerinum), saga (Adenathera microsperma), singkong (Manihot utilisima), karet (Havea brasiliensis), nenas (Ananas comosus), kelakai (Stenochlaena ralustris), buah nangka (Artocarpus integra) and other fruits.
 Keywords: Density, food, kelasi, population

Examining the Use of Auditory Signals as “Attention-Getters” in Zoo-Housed Gorillas (Gorilla gorilla gorilla) and Orangutans (Pongo pygmaeus and Hybrid)

“Attention-getters” are proposed to be gestures that function to attract the attention of a recipient and therefore allow further communication to take place. Their use is an indicator of intentional communication and thus of great interest to researchers in the field of language evolution. However, there is conflicting evidence as to whether nonhuman primates use attention-getters, both in conspecific interactions and in interactions with humans. We examined whether zoo-housed orangutans (Pongo pygmaeus and hybrid [Pongo pygmaeus × Pongo abelii]) and gorillas (Gorilla gorilla gorilla) used auditory signals to initiate visual communication with a human. To test this, a human experimenter stood with food in her hand and her back to the ape. If the ape produced an auditory signal, the experimenter either turned to face the ape or, in the control condition, away from the ape. We found that condition had no significant effect on whether the apes followed their initial auditory signal with a visual signal. Furthermore, the apes did not show greater persistence with, or elaboration of, their auditory signals when the human did not turn to face them, than when she did. In contrast, the apes showed significantly more persistence and elaboration of visual signals when the experimenter turned to face them. Our results suggest that while the orangutans and gorillas were able to discriminate human visual attention and use visual gestures accordingly, they did not attempt to manipulate this attention through the use of auditory behaviors to initiate visual communication.

Characteristic and Diversity Vegetation of Bukit Tiga Puluh National Park as Dietary Sources for Reintroduced Sumatran Orang Utan (Pongo abelii Lesson)

<p>The population of Sumatran orang utan in natural habitat has been declined and threatened with extinction. The orang utanreintroduction program is expected to increase breeding and population in nature. This study aimed to analyze the important value index of vegetation as well as the diversity and abundance species of Bukit Tiga Puluh National Park (BTNP) as dietary sources for reintroduced Sumatran orang utan. The research was conducted during two years from 2015 to 2016. The data collection for flora characteristics is done through the vegetation analysis with strip transects method. Plots were selected by stratification method based on the resort management and the land cover, like primary and secondary forests. Total flora species on a plot of 2.8<br />ha were identified about 301 species. The highest variation found in Suo-Suo Resort (139 species) and the lowest in Talang Lakat Resort (82 species). The dominant species have been found were Eugenia grandiflora O. Berg, Macaranga lowii King ex Hook.f., Shore iliginosa Foxw., and Tarrietia rubiginosa Kostern. Vegetation chararacteristic to be identified were tree density of 350-552.5 individuals/ha, species diversity index of 2.86-4.19, and abundance index of 32.1087.35. It also identified that vegetation characteristic among resort and land cover were different (p <0.05). Moreover, there were about 110 species of tree plants including of 31 families that found as dietary sources for orang utan and leaves became the highest plant parts which consumed by orang utans (41.8%) compared to other parts. Based on area size, ecosystem types as well as vegetation composition and variation, BTNP may support the increasing population of orang utans. However, there needs to be considered that other<br />aspects such as high human activity within the conservation area, particularly by Talang Mamak tribe communities, may cause unsuccessful achievement on reintroduction program of orang utan.</p>

The contribution of forest remnants within industrial area to threatened mammal conservation: A case study in liquefied natural gas industry in Bontang, Indonesia

Abstract. Sudrajat, Putro MD. 2019. The contribution of forest remnants within industrial area to endemic and threatened mammal conservation: A case study in liquefied natural gas industry in Bontang, East Kalimantan, Indonesia. Biodiversitas 20: 2257-2265. Tropical forests harbor high biodiversity, while natural protected area is one of the approaches for biodiversity conservation. However, the conversion of natural forests for various purposes has caused forest fragmentation. A novel strategy of conservation is proposed in the form of protected area within industrial estate as the contribution of industrial company in biodiversity conservation. The purpose of this study is to document the endemic and threatened species of mammals existing at two forest fragments with extent of 15 ha and 7.4 ha in a natural gas refinery industry area in Bontang, East Kalimantan and their potential as biodiversity conservation areas. Mammals were monitored at the two forest fragments through direct surveys, trace identification, mist nets, and camera traps. The results of the study show that according to IUCN Red List there were 23 mammal species (belonging to 18 genera, 15 families and six orders) of conservation concern found within the forest fragments including one species is under Critically Endangered, two are Endangered, four are Vulnerable, ten are Least Concern, one is Near Threatened and three are Not Evaluated. Four of those species are considered as endemic, namely Bornean orangutan, Pongo pygmaeus morio, Müller’s gibbon, Hylobates muelleri, Proboscis monkey, Nasalis larvatus and East Bornean slow loris, Nycticebus menagensis. These findings suggest that forest fragments located in the environment of industrial estate can be considered as important conservation strategy if they are well preserved and maintained.

Densities of Bornean orang-utans (Pongo pygmaeus morio) in heavily degraded forest and oil palm plantations in Sabah, Borneo.

The conversion of forest to agriculture continues to contribute to the loss and fragmentation of remaining orang‐utan habitat. There are still few published estimates of orang‐utan densities in these heavily modified agricultural areas to inform range‐wide population assessments and conservation strategies. In addition, little is known about what landscape features promote orang‐utan habitat use. Using indirect nest count methods, we implemented surveys and estimated population densities of the Northeast Bornean orang‐utan (Pongo pygmaeus morio) across the continuous logged forest and forest remnants in a recently salvage‐logged area and oil palm plantations in Sabah, Malaysian Borneo. We then assessed the influence of landscape features and forest structural metrics obtained from LiDAR data on estimates of orang‐utan density. Recent salvage logging appeared to have a little short‐term effect on orang‐utan density (2.35 ind/km 2), which remained similar to recovering logged forest nearby (2.32 ind/km 2). Orang‐utans were also present in remnant forest patches in oil palm plantations, but at significantly lower numbers (0.82 ind/km 2) than nearby logged forest and salvage‐logged areas. Densities were strongly influenced by variation in canopy height but were not associated with other potential covariates. Our findings suggest that orang‐utans currently exist, at least in the short‐term, within human‐modified landscapes, providing that remnant forest patches remain. We urge greater recognition of the role that these degraded habitats can have in supporting orang‐utan populations, and that future range‐wide analyses and conservation strategies better incorporate data from human‐modified landscapes.

Changes to Sabah's orangutan population in recent times: 2002-2017.

The Bornean orangutan is critically endangered and monitoring its population is needed to inform effective conservation management. In this paper, we present results of 2014–17 aerial nest surveys of the major orangutan populations in Sabah and compare them with baseline data produced during surveys conducted in 2002–03 using similar methods. Our results show three important points: a) by increasing the survey effort (estimated at 15–25% cover), sparsely scattered orangutan sub-populations not recorded in the previous aerial surveys were located and the accuracy of the nest count estimates is expected to improve; b) large populations in the interior forests of Sabah, occupying sustainably managed logged and unlogged forests, have been stable over 15 years and are of vital importance for the species’ conservation; c) fragmented populations located in eastern Sabah, that are surrounded by extensive oil palm plantations, have declined at varying rates.

These orangutan moms scratch to get their kid’s attention

These orangutan moms scratch to get their kid’s attention

High Satellite Repeat Turnover in Great Apes Studied with Short- and Long-Read Technologies.

Satellite repeats are a structural component of centromeres and telomeres, and in some instances, their divergence is known to drive speciation. Due to their highly repetitive nature, satellite sequences have been understudied and underrepresented in genome assemblies. To investigate their turnover in great apes, we studied satellite repeats of unit sizes up to 50 bp in human, chimpanzee, bonobo, gorilla, and Sumatran and Bornean orangutans, using unassembled short and long sequencing reads. The density of satellite repeats, as identified from accurate short reads (Illumina), varied greatly among great ape genomes. These were dominated by a handful of abundant repeated motifs, frequently shared among species, which formed two groups: 1) the (AATGG)n repeat (critical for heat shock response) and its derivatives; and 2) subtelomeric 32-mers involved in telomeric metabolism. Using the densities of abundant repeats, individuals could be classified into species. However, clustering did not reproduce the accepted species phylogeny, suggesting rapid repeat evolution. Several abundant repeats were enriched in males versus females; using Y chromosome assemblies or Fluorescent In Situ Hybridization, we validated their location on the Y. Finally, applying a novel computational tool, we identified many satellite repeats completely embedded within long Oxford Nanopore and Pacific Biosciences reads. Such repeats were up to 59 kb in length and consisted of perfect repeats interspersed with other similar sequences. Our results based on sequencing reads generated with three different technologies provide the first detailed characterization of great ape satellite repeats, and open new avenues for exploring their functions.

Three-dimensional geometric morphometric analysis of the distal radius insertion sites of the palmar radiocarpal ligaments in hominoid primates.

To identify anatomic differences in the insertion sites of the palmar radiocarpal ligaments in different species of hominoid primates that may be related to their different types of locomotion. We have used three-dimensional geometric morphometrics (3D GM) to analyze the distal radius ligament insertion sites in 31 Homo sapiens, 25 Pan troglodytes, 31 Gorilla gorilla, and 15 Pongo pygmaeus. We have also dissected the radioscaphocapitate (RSC), long radiolunate (LRL) and short radiolunate (SRL) ligaments in six H. sapiens and five P. troglodytes to obtain quantitative values that were then compared with the results of the 3D GM analysis. H. sapiens had a relatively larger insertion site of the RSC + LRL ligament than the other hominoid primates. P. pygmaeus and P. troglodytes had a relatively large SRL ligament insertion site with a palmar orientation. In G. gorilla, the two ligament insertion sites were relatively smaller and the SRL insertion site had an ulnopalmar orientation. The morphological differences observed can be related to the types of locomotion used by the different species and to quantitative data obtained from the dissection of ligaments in H. sapiens and P. troglodytes. 3D GM analysis of ligament insertion sites can help in interpreting the types of locomotion used by extinct hominoid primates through the analysis of preserved fossilized fragments of the distal radius.

Are Male Orangutans a Threat to Infants? Evidence of Mother–Offspring Counterstrategies to Infanticide in Bornean Orangutans (Pongo pygmaeus wurmbii)

Sexually selected infanticide by males is widespread in primates. Female primates employ a variety of strategies to reduce infanticide risk. While infanticide has never been directly observed in wild orangutans (Pongo spp.), their slow life history makes infants vulnerable to infanticide. The mating strategies of female orangutans include polyandrous and postconceptive mating that may serve to increase paternity confusion, an infanticide avoidance strategy. Here, we investigate whether female orangutans alter their social interactions with males as another infanticide avoidance strategy. We hypothesize that females with younger offspring avoid males and that the distance between mother and offspring decreases in the presence of males. We use long-term behavioral data collected between 1994 and 2016 from Bornean orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, Indonesia, to test whether the sexual selection hypothesis for infanticide helps explain aspects of orangutan social behavior. We found that mothers with offspring 6 yr. old and females without offspring. In addition, the distance between a mother–offspring dyad showed a statistically significant decrease in the presence of males, but not females. Our results are consistent with the hypothesis that female orangutans employ strategies to reduce infanticide risk in their social interactions. Because orangutans have a high fission–fusion dynamic, they have flexibility in manipulating social interactions as a counterinfanticide strategy. Our results suggest that infanticide by males is a selective pressure shaping female orangutan social behavior.

Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo

Research on captive and wild great apes has established that they employ large repertoires of intentional gestural signals to achieve desired goals. However, gestural research has focused on African great apes, with orang-utan data limited to a few captive studies. We address this gap by describing gesture use in wild Southwest Bornean orang-utan (Pongo pygmaeus wurmbii) mother and offspring pairs. We conducted focal follows on 16 individuals in the Sabangau peat-swamp forest in Borneo, Indonesia. The resulting 681 h of video footage yielded 1299 communicative signals: 858 vocal signals and 441 gestural signals. Eleven vocal signal types and 21 gesture types met the criteria for inclusion in the repertoire; however, the gestural repertoire did not approach asymptote and further gesture types will likely be identified in the future. Signalers used gestures of any modality in higher frequency when the recipient was paying visual attention, and took the recipient’s visual attention into account when selecting gesture modalities. Orang-utans employed hands and arms more than legs and feet in gesturing, but were more flexible in their choice of limb than chimpanzees using the same gestures. Orang-utans were highly responsive to gestural requests, using them to achieve eight goals and, where successful, responding either before gesturing ended or in <1 s in 90% of communications. Our findings on the range of gesture types and impact of visual attention support findings from captive orang-utans; and those on responsiveness and limb use highlight the importance of studying ape communication in the social and ecological context to which it is adapted.

Conserving orangutans one classroom at a time: evaluating the effectiveness of a wildlife education program for school‐aged children in Indonesia

AbstractEnvironmental education is a cornerstone of many wildlife conservation programs, and measuring the impact of such education initiatives is imperative for evaluating their effectiveness in achieving conservation goals. For over 15 years, the Gunung Palung Orangutan Conservation Program (GPOCP) has been working to protect wild Bornean orangutans Pongo pygmaeus wurmbii living in and around Gunung Palung National Park in West Kalimantan, Indonesia. In 2015, we carried out a series of six Environmental Education Expeditions to communities in the remote districts surrounding the Park, engaging 1519 elementary (n = 770) and junior/senior high school (n = 749) students across 24 schools. Before and after engaging with our environmental education activities students were given surveys to assess their knowledge about and attitudes toward orangutans. We found that our educational activities led to 13.6–40.4% increases in student knowledge about orangutans and substantial shifts toward more positive attitudes about conservation, but that many students do not believe that they personally can make a difference. Empowerment may be a key need to link wildlife education to environmental action.

Enamel Distribution in 3D: Is Enamel Thickness More Uneven in the Upper Second Molars of Durophagous Hominoids?

Enamel thickness is not uniform across the dental crown of primates. It has been suggested that enamel distribution could be used in taxonomy or for ecological inferences. For instance, the thickness of molar enamel in mammals consuming hard food is expected to be uneven, despite differing reports on extant and extinct apes. Overall estimations of average and relative enamel thickness may mask the details of enamel distribution in complex teeth such as molars. Investigating enamel distribution and its purported relationship with ecology or phylogeny would require more detailed assessments. This paper aims to assess whether apes that consume hard foods on a regular basis, such as Pongo pygmaeus, can be characterized by the evenness or unevenness of enamel thickness. To do so, we combined topographic maps and distribution histograms of enamel thickness with cumulative profiles of its variation, or “pachymetric profiles”. We investigated a sample of 25 unworn hominoid upper second molars scanned by X-ray microtomography, and further compared this to a sample of 32 cercopithecines and colobines. Topographic maps show uniformly thin enamel for Gorilla gorilla and Hylobates sp., unevenly thin enamel for Pan paniscus and Pan troglodytes, and unevenly thick enamel for Pongo pygmaeus. The skewness of enamel distribution does not distinguish between ape species, but does separate apes from OldWorld monkeys. Contrary to previous reports on OldWorld monkeys, the slope of enamel thickness profiles, or pachymetric slope, does not predict the diet of extant apes. However, it does separate the Pan genus, which is characterized by a higher pachymetric slope indicating more uneven enamel distribution compared to other apes. The uneven thickness of enamel distribution observed on topographic maps for P. pygmaeus is not supported by its low pachymetric slope, which instead indicates uniform enamel distribution. This discrepancy in the results obtained for P. pygmaeus can be interpreted as an evolutionary tradeoff between fine-scale versus overall enamel distribution. On the one hand, unevenly thick enamel at a fine scale, combined with strongly decussated enamel as observed in P. pygmaeus, is expected to increase local resistance to crack propagation. On the other hand, uniformly thick enamel at the overall scale would improve the overall resilience of the enamel in coping with challenging food on a daily basis. Although understanding the effects of ecology on enamel distribution in apes requires further investigation, the results presented in this paper confirm the interest of enamel distribution for taxonomy and phylogeny.

Orangutans (Pongo pygmaeus and Hybrid) and Gorillas (Gorilla gorilla gorilla) Modify Their Visual, but Not Auditory, Communicative Behaviors, Depending on the Attentional State of a Human Experimenter

The ability to judge the visual attention of others is a key aspect of human social cognition and communication. While evidence has shown that chimpanzees can discriminate human attention based on eye cues alone, findings for gorillas and orangutans have been less consistent. In addition, it is currently unclear whether these gorillas and orangutans attempt to attract the visual attention of inattentive recipients using “attention-getting” behaviors. We replicated and extended previous work by testing whether six orangutans (Pongo pygmaeus and hybrid) and six gorillas (Gorilla gorilla gorilla) modified the use of their visual and auditory signals based on the attentional state of a human experimenter. We recorded all communicative behaviors produced by the apes for 30 s while a human experimenter stood in front of them with a food reward in a variety of postures, both visually attentive (facing the apes) and inattentive (body and/or head facing away or eyes covered). Both species produced visual behaviors more often when the experimenter was looking at them than when she had her face turned away, but only the orangutans discriminated attention based on eye cues alone. When we removed human-reared apes from the analyses (N = 3), mother-reared apes showed sensitivity to eye cues from the experimenter. However, further analyses found that the orangutans and gorillas relied more heavily on the body and head orientation of the experimenter than on her eye cues. Neither species produced more vocalizations or nonvocal auditory behaviors, such as mesh and object banging, mesh rubbing, or clapping, in the inattentive, than attentive, conditions. Our results reveal that while orangutans and gorillas preferentially use visual gestures when a human is attending to them, they do not appear to produce auditory behaviors, including vocalizations, with the intention of manipulating the recipient’s attention state.

Threats and lessons learned from past orangutan conservation strategies in Sarawak, Malaysia

In 2015, the Sarawak Government made a public pledge to stop illegal logging in the State, to create more national parks, and to move towards a zero-loss policy of orangutans and their habitats in Sarawak. Conservationists welcomed this policy in view that threat level for the Bornean orangutans under the IUCN Red List has been upgraded to Critically Endangered in 2016. The main threats to orangutan survival include habitat degradation and forest loss which is rapidly driven by large-scale development of unsustainable land-use change. The cultural taboo against orangutan hunting is slowly eroding with evidence of the species being killed in vulnerable areas. We discussed shortfalls of conservation responses in the past 60 years in Sarawak which included unknown rate of illegal orangutan killings, inadequate law enforcement, and incomprehensive community development strategies. The recommendations to address these shortfalls then include: a) inter-agency collaboration for orangutan population monitoring, b) technological application and intelligence networks to intensify enforcement strategies, c) alternative community livelihood development and self-enforcement, and d) increased public support for conservation policies. The implementation of the zero-loss policy is anticipated to emphasize the needs for orangutan protection amid rapid development plans around critical habitats.

KARAKTERISTIK DAN KERAPATAN SARANG ORANGUTAN (Pongo pygmaeus wurmbii) DI DUA TIPE HABITAT YANG BERBEDA DI STASIUN PENELITIAN CABANG PANTI TAMAN NASIONAL GUNUNG PALUNG KABUPATEN KAYONG UTARA

Cabang Panti Research Station has diverse habitat, therefore the researchers are interested to conducting a research on the characteristic and densities of Orangutan nests (Pongo pygmaeus wurmbii) in two on different habitat namely in alluvial bench forests and peat swamp forests. The purpose of this study want to see a comparison of the characteristic and density as an Orangutan nest (Pongo pygmaeus wurmbii) in two different habitat types. The method used in this research was Line transect survey. The nests were searched by walking through the midline while observing and recording the discovered nests in the line transect. Based on the result of the Independent Sample Test, it showed that there was no difference of tree trunk diameter, but there was a difference of height of the nest tree and the nest itself. The nest position was almost similar which was position 3 (tip top) in the amount of 83% in alluvial bench habitat while it was position 1 (among the main branching) in the amount of 42% and 3 (the canopy of the tree in form of fork) in the amount of 42%. The class of the nest which mostly found in both habitat was nest class D in the amount of 50% in the alluvial bench habitat and 83% in the peat swamp forest. The type of tree which was mostly used by the Orangutan to create their nest in both habitat was Shorea spp. The densities of the nest of Orangutan was 30 nest/km² in the alluvial bench habitat and 60 nest/km² in the peat swamp habitat. Keyword: Cabang Panti, Nest Characteristics, Nest Densities, Orangutan

The body center of mass in primates: Is it more caudal than in other quadrupedal mammals?

Whole body center of mass (BCoM) position values are lacking for a comparative sample of primates. Therefore, it still remains unknown whether the BCoM in primates is more posteriorly located than in other mammals. The aim of the present report is to provide data for a large sample of primate species and to compare the position of the BCoM in primates to non-primate mammals. We collected morphometrics on eight primate species belonging to various families: Hylobatidae (Nomascus grabriellae, Nomascus Siki), Cercopithecidae (Cercopithecus roloway, Cercopithecus lhoesti, Colobus guereza, Trachypithecus francoisi), Cebidae (Sapajus xanthosternos), and Atelidae (Ateles fusciceps). Using a geometric model, we assessed the position of the BCoM in a natural quadrupedal posture and in a control posture. To complete our comparative sample with a wider range of morphotypes, we added the data available in the literature for hominoids (Pan paniscus, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus, Hylobates lar) and another cercopithecoid species (Papio anubis). We also evaluated the phylogenetic signal of the position of the BCoM in primates. The variation in the position of the BCoM in primates is very large, ranging from 40% of the distance between the hip and the shoulder in Ateles fusciceps to 63% in Hylobates lar. We observed a strong phylogenetic signal for this trait: hominoid species, as well as the baboon, have a cranial BCoM relative to the midline between the hip and the shoulder, arboreal cercopithecoids and the spider monkey have a caudal BCoM, and the capuchin monkey has a BCoM positioned at mid-trunk. The variation observed in non-primate quadrupedal mammals lies inside the variation range of primates, from 51% in Felis catus to 63% in Canis familiaris. The BCoM of primates is not more posteriorly located than in other quadrupedal mammals; however, there is a substantial range of variation in primates, from caudal (in arboreal quadrupeds) to cranial (in hominoids and terrestrial quadrupeds) positions. This variation is related to a phylogenetic model that suggests stabilizing selection for this trait. It seems that the BCoM position mostly depends of the size of the appendicular system (i.e., limbs) and the tail. Therefore, it may also reflect a general trend in quadrupedal mammals with arboreal species exhibiting a caudal BCoM and terrestrial species exhibiting a cranial BCoM. These results are discussed in the context of the locomotor evolution of primates including locomotor habits and gait mechanics. We also propose a new "passive" mechanism for the explanation of the particular weight support pattern observed in primates with tails.

The Bornean orangutan (Pongo pygmaeus wurmbii) density in a logging concession of Hulu Belantikan, Central Kalimantan, Indonesia

Abstract. Sapari I, Perwitasari-Farajallah D, Utami Atmoko SS. 2019. The Bornean orangutan (Pongo pygmaeus wurmbii) density in a logging concession of Hulu Belantikan, Central Kalimantan, Indonesia. Biodiversitas 20: 878-883. The Bornean orangutan is currently categorized as a critically endangered species. It is found in natural forests in Borneo, where about 78% of the total population is found outside protected areas, of which 29% is in logging concessions. This study aimed to analyze the density of the orangutan population and the abundance of fruiting plants in a logging concession and Protection Forest (Hutan Lindung) in the Hulu Belantikan forests in Lamandau District, Central Kalimantan, Indonesia. Research and data collection was conducted between December 2013 to October 2014. Orangutan population density was calculated using line transect methodology based on nest counts. Abundance of fruit plants was calculated using the fruit trail method. The highest orangutan density, 4.8 individuals/km2, was found in Protection Forest; and the lowest density, 0.4 individuals/km2, was in [Sopanan] the 2013 logging block. Observations in the logging area indicated that selective logging could alter the structure and gap of the canopy and reduce the proportion of large trees. Changes in forest structure resulted in negative effects on the density of the orangutan population. The remaining degraded forests can still be a valuable resource for the orangutan. As long as the disturbance is not intensive, orangutans will retain access to the less disturbed forest nearby and to forests that are still connected to primary forests. The existence of Protection Forest and old logged-over forests around logging blocks are very important for conservation, providing refugia for orangutans and other species when logging occurs.