Kloss Gibbons Research Articles

Tooth chipping prevalence and patterns in extant primates.

A tooth chip occurs when a hard object forcefully contacts the surface of the tooth, typically removing enamel from the occlusal edge. In this study, chipping patterns in extant primates were compared, and hard-object-feeding assessed alongside other factors (e.g., grit mastication and dental properties), to elucidate dietary and behavioral inferences in archeological and paleontological samples. Thirteen species of extant primates were studied, including eight species within the Cercopithecidae, two within the Ceboidea, and three within the Hominoidea. Four additional species were also incorporated from the literature for some of the analyses. The severity (Grade 1-3), position (buccal, lingual, mesial, and distal) and number of tooth fractures were recorded for each specimen. Species considered hard-object-feeding specialists presented higher rates of chipping, with sakis, mandrills, sooty mangabeys and Raffles' banded langurs having high chipping rates (28.3%, 36.7%, 48.4%, and 34.7% of teeth, respectively). Species that seasonally eat harder foods had intermediate chipping frequencies (e.g., brown woolly monkeys: 18.5%), and those that less commonly consume hard food items had the lowest chipping frequencies (e.g., Kloss gibbon: 7.3%; chimpanzees: 4.4%). The results suggest hard food mastication influences differences in chipping prevalence among the species studied. Although Homo fossil samples show high rates of chipping comparable to hard-object-feeding extant primates, they display a different pattern of chipping, supporting the hypothesis that these fractures are mostly non-food related (e.g., grit mastication in Homo naledi; non-masticatory tooth use in Neanderthals).

Distribution survey of Kloss’s Gibbons (Hylobates klosii) in Mentawai Islands, Indonesia

Abstract. Setiawan A, Simanjuntak C, Saumanuk I, Tateburuk D, Dinata Y, Liswanto D, Rafiastanto A. 2020. Distribution survey of Kloss’s Gibbons (Hylobates klosii) in Mentawai Islands, Indonesia. Biodiversitas 21: 2224-2232. The aim of this study was to assess the population density, distribution, habitats, and threats of Kloss’s gibbon (Hylobates klossii) in the Mentawai Islands, Indonesia. In 2011-2012 we conducted a survey on Siberut Island, outside of the National Park, as well as a short visit to Sipora, North Pagai, and South Pagai. From March to September 2017, we surveyed once again some previous localities on the Siberut and Sipora islands to keep up to date with recent developments on the ground. On Siberut we used an auditory sampling method through fixed point counts, combined with line transects, to estimate the gibbon densities. In total, 113-morning calls were recorded from 13 Listening Points; 75 of these were used for density calculations. We recorded 35 individuals based on direct sightings during 66.4 km of transect distance walked. We found 13 localities outside of Siberut National Park that still have Kloss's gibbons; densities varied between 1.04group/km2 to 4.16 group/km2. No gibbons were found and heard during the short survey in Sipora and South Pagai, though we found a group of gibbons in North Pagai. Our 2017 survey revealed massive habitat changes in South Siberut. Previously existing forest localities in South Siberut were gone due to road construction, agriculture expansion, and logging.

First estimates of primate density and abundance in Siberut National Park, Mentawai Islands, Indonesia

AbstractIn 2011 we carried out the first systematic survey to determine the density and abundance of endemic forest primates in Siberut National Park, in the Mentawai Islands of West Sumatra, Indonesia. Distance sampling was employed to survey 18 transects located systematically throughout the Park, yielding a total survey effort of 192 km and 285 observations of primates for data analysis. From density estimates for the four resident primate species, the Siberut langur Presbytis siberu, the pig-tailed snub-nosed langur Simias concolor, Kloss's gibbon Hylobates klossii and the Siberut macaque Macaca siberu, we extrapolated a total population of c. 51,000 primates within the Park. We conclude that Siberut National Park is of major significance for the continued survival of Siberut's endemic primates, and provide recommendations to help ensure that it will continue to function as a refuge for primates.

Kloss gibbon (Hylobates klossii) behavior facilitates the avoidance of human predation in the Peleonan forest, Siberut Island, Indonesia.

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and have been subject to human predation for more than 2000 years in the absence of any other significant predators. We investigate the behavior of Kloss gibbons that may be attributed to avoiding human predation. We observed Kloss gibbons in the Peleonan forest in the north of Siberut Island, the northernmost of the Mentawai island chain, over 18 months in 2007 and 2008, and collected data on their singing behavior, the number of individuals present during different conditions and their responses to humans. We examine behaviors that may reduce the risk of predation by humans during singing (the most conspicuous gibbon behavior), daily non-singing activities and encounters with humans. The individual risk of being stalked by hunters is reduced by singing in same-sex choruses and the risk of successful capture by hunters during singing is reduced by singing less often during daylight hours and by leaving the location of male pre-dawn singing before full light (reducing the visual signal to hunters). Groups in the Peleonan also fission during non-singing daily activity and rarely engage in play or grooming, enhancing the crypticity of their monochromatic black pelage in the canopy. We also observed a coordinated response to the presence of humans, wherein one adult individual acted as a "decoy" by approaching and distracting human observers, while other group members fled silently in multiple directions. "Decoy" behavior occurred on 31% of 96 encounters with unhabituated Kloss gibbons that detected our presence. "Decoy" individuals may put themselves at risk to increase the survival of related immatures (and adult females with infants) who have a greater risk of predation. We argue that, in combination, these behaviors are an evolved response to a long history of predation by humans.

Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and are one of only two gibbon species in which mated pairs do not sing duets. This is the first long-term study of the factors influencing the singing activity of Kloss gibbons within a northern Siberut Island population and follows two previous studies in central Siberut nearly 30years ago. We collected data on the presence/absence of male and female singing within the study area on 198days and within a focal group on 47days. Rainfall during the time period in which they normally sing inhibits singing in both males and females. Our study supports the hypothesis that male and female songs function in intrasexual resource defence, as singing is associated with singing by same-sex neighbours, and same-sex choruses are more likely to occur after one or more days of silence (from that sex), suggesting there is pressure for individuals to communicate with same-sex neighbours regularly. Singing was not coordinated within a mated pair, suggesting that vocal coordination of the pair has been lost with the loss of the duet and that Kloss gibbon songs do not convey information to neighbours about the strength of the pair bond. On days when males sang predawn, females were more likely to sing after dawn and earlier in the morning. Additionally, the number of groups singing in female choruses was positively associated with the number of males that had sung in the predawn male chorus. We suggest that female songs have an intersexual territory defence as well as an intrasexual function.

Peat swamp forest supports high primate densities on Siberut Island, Sumatra, Indonesia

Although South-east Asia harbours most of the world's tropical peatlands relatively little is known about the primate communities of the associated habitat, the peat swamp forest. To understand better the role of tropical peat swamp forests for the conservation of primates in general, and for the endemic primates of the Mentawai Islands in particular, we conducted a line transect survey in a 12.5-km 2 section of peat swamp forest in northern Siberut. A total of 215 records of all four Siberut primates (Endangered Kloss's gibbon Hylobates klossii , Endangered Mentawai langur Presbytis potenziani , Vulnerable Siberut macaque Macaca siberu and Critically Endangered pig-tailed langur Simias concolor ) were obtained. Pig-tailed langurs (65.5 km -2 , 95% confidence interval, CI, 41.9–102.6) and Siberut macaques (35.8 km -2 , 95% CI 25.5–50.4) were the most common species, with density estimates similar to (pig-tailed langur) or greater than (Siberut macaque) those in adjacent lowland rainforest on mineral soil. Density estimates of the Mentawai langur (2.7 km -2 , 95% CI 1.3–5.3) and Kloss's gibbon (1.0 km -2 , 95% CI 0.3–2.8) were approximately one-third and one-tenth, respectively, of the adjacent lowland rainforest. Given that resource density and diversity in peat swamp forest are probably lower than that of lowland rainforest, primate densities appear to be relatively high, with overall primate biomass (881 kg km -2 ) exceeding values for lowland rainforest on mineral soil. Our results underline the general importance that peat swamp forests may have for South-east Asian primates and for two island endemic species in particular.

Abundance and community structure of Mentawai primates in the Peleonan forest, north Siberut, Indonesia

The island of Siberut in the Mentawai Archipelago, west of Sumatra, Indonesia, supports four of the five primate species endemic to the Archipelago, all categorized as threatened on the IUCN Red List. As a baseline for future research on the ecology and conservation of Siberut's primates we used a line-transect approach to survey primates in the Peleonan forest, site of the Siberut Conservation Project in northern Siberut. In 104 km of surveys we made a total of 391 observations of primates and estimated density and population sizes for the Project's 10.7 km2 main study site. Overall primate biomass density was estimated to be 697 kg km-2 and abundances, in individuals km-2, were: pig-tailed snub-nosed langur Simias concolor, 53.1; Siberut macaque Macaca siberu, 16.2; Kloss's gibbon Hylobates klossii, 8.9; Mentawai langur Presbytis potenziani, 8.2. These results confirm those from earlier studies that in undisturbed and unhunted primary forests S. concolor is more successful than the sympatrically occurring P. potenziani. Results for all species suggest considerable population sizes on the island and underline its importance for the conservation of Mentawai primates.

Acoustic Niches of Siberut Primates

The loud calls nonhuman primates use in long-distance communication have supposedly been selected for efficient information transfer in the habitat. The differential effects of scattering and reverberation and the masking effects of background noise predict that loud calls produced in rain forest habitats should be low-pitched and whistle-like with low-frequency modulation. Callers may also use particular calling posts or times of day with reduced background noise to increase the efficacy of sound transmission. We studied the loud calls of the 4 sympatric primate species on Siberut Island. Only Kloss gibbons (Hylobates klossii) fulfilled the predictions regarding both the structure and use of calls. Though the other 3 species – Mentawai macaques (Macaca siberu), pig-tailed langurs (Simias concolor), and Mentawai leaf monkeys (Presbytis potenziani) – also concentrated their main energies in the spectral window with the lowest background noise, their calls were not adapted to long-range transmission. All 4 species produced loud calls exclusively no lower than 18 m above ground, but food abundance and shelter in the canopy may also be factors. Though all 4 species produced the majority of loud calls in the morning, it was not the only time of day with reduced background noise. We suggest that phylogenetic inheritance may better explain the structure of calls than adaptation to the habitat. In sum, the observed usage of spectral and temporal niches is not solely an adaptation to the sound profile of the habitat, though it clearly improves their transmission.

A Conservation Action Plan for the Mentawai Primates

In this Conservation Action Plan, I evaluate the status of and make conservation recommendations for the four endemic primates of the Mentawai Islands: Kloss's gibbon (Hylobates klossii primates of the Mentawai Islands: Kloss's gibbon (Hylobates klossii primates of the Mentawai Islands: Kloss's gibbon ( ), the simakobu monkey (Simias concolor), the Mentawai langur (Presbytis potenziani langur (Presbytis potenziani langur ( ), and the Mentawai macaque (Macaca pagensis). There are two subspecies of each of the cercopi- thecines. They are threatened mainly by hunting and commercial logging. This action plan follows up on the recommendations made for the Mentawai primates in the IUCN/SSC Primate Specialist Group's Action Plan for Asian Primate Conservation: 1987-91 by Ardith Eudey, and includes data and recommendations from researchers who have studied them since 1980. I also include a brief history of conservation action in the Mentawai Islands to put these recommendations in a historical context. I recommend the following conservation status changes: Kloss's gibbon, Endangered; simakobu monkey, Critically Endangered; Mentawai langur, Endangered; and Mentawai macaque, Vulnerable. The largest populations of the four species can be found in Siberut National Park on the largest and northernmost island, but all but Kloss's gibbon have distinct subspecies on the southern islands of Sipora, North Pagai, and South Pagai, and these are urgently in need of protective measures. The national park is remote and diffi cult to access by researchers and tourists. I suggest the following conservation actions: 1) increased protection for the Siberut National Park, which currently lacks enforcement; 2) formal protection of the Peleonan forest in North Siberut, which is home to unusually high primate populations and is easily accessible; 3) protect areas in the Pagai Islands by cooperating with a logging corporation that has practiced sustainable logging techniques there since 1971; 4) conservation education, especially regarding hunting; and 5) the development of alternative economic models for the local people to reduce the likelihood of selling

Calling in wild silvery gibbons (Hylobates moloch) in Java (Indonesia): behavior, phylogeny, and conservation

Hardly any behavioral data are available for the silvery gibbon (Hylobates moloch), an endangered primate that is endemic to the island of Java, Indonesia. We studied the singing behavior of the easternmost population of this species in the Dieng mountains, central Java, in 1998-1999. We aimed to document the timing of singing, quantify the amount of singing by the respective sexes, and explore the role of bioacoustics in density estimation. A total of 122 song bouts in at least 12 groups were monitored. No duet songs were heard. Most of the song bouts (91.5%) were female solo song bouts or female scream bouts. In contrast to an earlier study on the westernmost population of silvery gibbons, during which few if any male songs were heard, at least 8.5% of the song bouts in our study were male solo song bouts. They were significantly longer in duration than the female songs. All male song bouts uttered before dawn (0520 hr) were produced in a chorus fashion, with at least three individuals participating. Choruses occurred about once every 8.5 days, and lasted longer and occurred earlier than female solo song bouts. Most male songs (60%) started between 0355-0440 hr, when it was still dark. All female songs, in contrast, started after 0500 hr, and female singing activity peaked around 0600. Regular male singing, male chorusing, and regular predawn singing have not previously been reported for silvery gibbons. Similarly separated periods of male and female solo songs and the absence of duetting have been observed in Kloss's gibbons (H. klossii) on the Mentawai Islands, and may represent synapomorphies shared by both species. The pronounced individual-specific song characteristics of silvery gibbons allow accurate mapping of groups. The density of gibbons at our study site was established to be 1.9-3.7 groups/km2, corresponding to 6.7-13.1 individuals/km2. We reassess the suitability of gibbon songs as a means of estimating the density and size of gibbon populations, and discuss the proximate causes for the absence of duetting in silvery gibbons.

New population estimates for the endemic Kloss's gibbon Hylobates klossii on the Mentawai Islands, Indonesia

The Vulnerable endemic Kloss's gibbon was surveyed throughout the Mentawai Islands, Sumatra, Indonesia, using a call-based method. Populations were estimated by extrapolating from local densities using recent assessments of remaining forest cover. About 20,000–25,000 Kloss's gibbons remain in nearly 3,000 km2 of forest (about 40% of the islands' total area). This number is markedly lower than a 1980 estimate of 36,000 on the northernmost island of Siberut. Conservation action to preserve the remaining populations should focus on strengthening the enforcement of regulations in Siberut National Park, formally protecting the Peleonan forest in north Siberut, and cooperating with a logging company in North and South Pagai to protect the populations in the company's self-established conservation and buffer areas.

Human predation and Kloss's gibbon (Hylobates klossii) sleeping trees in Siberut Island, Indonesia.

Kloss's gibbons (Hylobates klossii) and Mentawai langurs (Presbytis potenziani) on Siberut Island, Indonesia, both sleep in emergent trees 34-55m tall, situated on crests and upper slopes of hills. They differ in that 91% of gibbon sleeping trees examined were free of lianas, whereas 89% of langur sleeping trees were draped with thick, woody lianas hanging from the branches to the ground. Because indigenous hunters climb lianas to shoot primates in treetops, gibbons are less susceptible than langurs to nocturnal human predation. Hence, the gibbons' preference for-and apparent control of-the limited supply of vineless trees gives them an advantage over langurs.

The ecology of singing in Kloss gibbons (Hylobates klossii) on Siberut Island, Indonesia

Data are presented from a study of habituated Kloss gibbons on Siberut Island, Indonesia. Male Kloss gibbons can sing at any time from 0100 to 1300 hr, but the majority of songs is concentrated in the hour before dawn. Female Kloss gibbons sing only after dawn and the song bout includes a dramatic visual display. Neither countersinging nor coordinated chorusing has been proved in either sex. Males sing before dawn as often as possible but are inhibited by wet nights and by minimum temperatures below 21.5°C; postdawn songs of both sexes are inhibited by rain. The occurrence of any particular type of song bout is independent of the occurrence of the other types. Song trees used by males and those used by females do not differ in height. Song trees emerged from the neighboring canopy more than other available trees of similar height in the gibbons’ home range. Female song trees were most abundant on the slopes and where the trees were tallest. Almost all the male’s night trees could have been used for singing from had the weather been suitable. There was a greater likelihood of the male’s traveling a long way to the day’s first fruit source on mornings when he sang before dawn than on mornings when he did not. Considerations of sound transmission through tropical rain forest reveal that the times and frequencies used for singing by Kloss gibbons are optimal for communicating with neighboring groups.

A Numerical Analysis of Tropical Rain Forest, Using Floristic and Structural Data, and Its Application to an Analysis of Gibbon Ranging Behaviour

(1) As part of a study of the manner in which Kloss gibbons use the forests available to them, data were collected in two study areas of Lowland Evergreen Rain forest on Siberut Island, Indonesia, from 2459 trees of at least 15-cm dbh along transects of quadrats the total area of which was 11.3 ha. The identity of each tree, its height and climber load, the abundance of Myrmecodia epiphytes, and the position of its crown within the neighbouring canopy were recorded. (2) These data were analysed using classification and ordination techniques and as a result nine forest types were derived. These could be interpreted ecologically. One was on dry level ground, one on wet level ground, one on peatswamp, two on major ridges, and four on minor ridges. These types were generally recognizable by indicator species, and that gibbons recognized them too was reflected in their behaviour. (3) Seven of the forest types, in twenty-two blocks, were in the 31-ha home range of the main study group of gibbons. The number of times that gibbons were seen feeding in a forest type was very highly correlated with the density of trees that were potential fruit sources for gibbons. (4) Female gibbons sang from those forest types with the trees that were tallest and above the break of slope. The gibbon group slept in those forest types in which the trees had a low frequency of the myrmecophilous epiphyte Myrmecodia tuberosa, presumably to avoid being bitten by ants. (5) Few meaningful correlations were found between forest type and specific activities. However, forest types such as peatswamp were under-used consistently, while others such as those on minor ridges were used disproportionately often for certain activities. This information allowed the conventional two-dimensional view of a home range to be extended to a four-dimensional view by including differential canopy use and changes in behaviour through the day.

Diet and feeding behaviour of kloss gibbons on Siberut Island, Indonesia.

Kloss gibbons are the same size and live in the same type of habitat as several other gibbon species, and consequently its diet would be expected to be similar to its closely related congeners. The diet is described in terms of the weight of food items, faecal remains, and time devoted to different foods. Aspects of feeding behaviour are then examined, such as changes in food choice through the day, the relationship between fruit size to feeding bouts and feeding rates, and the effect of forest type quality on ranging. A comparison is made between gibbon species. The diet of Kloss gibbons appears to differ from that of other gibbons in that it contained no tree leaves, and arthropods were a major part of the diet. Possible reasons for this are discussed.

Home range use by Kloss gibbons ( Hylobates klossii) on Siberut Island, Indonesia

A home range is a reservoir of resources which are distributed throughout its area and joined by pathways. These resources are used for different activities and at different times of day and while ‘space-time systems’ have been described for a few terrestrial mammals, no previous study has attempted a similar analysis for an arboreal mammal. Kloss gibbons were studied for two years on Siberut Island, Indonesia, and one group was habituated to an observer. The ranging patterns of this group are analysed in two, three and four dimensions with respect to the types of forest in which the animals lived. Finally, differences between the results of this and previous studies of Kloss gibbons are discussed and it is suggested that a home range can be more permanent than the animals within it.

Family formation strategies of Kloss's gibbons.

This study describes how adults of Kloss's gibbons (Hylobates klossii) inhabiting the central rain forest of Siberut Island, Indonesia, help their offspring achieve reproductive success. Adults of these monogamous apes exclude maturing offspring from the family and territory through intrasexual aggression. Adults may then assist the offspring to establish a territory contiguous to theirs. Aid may take the form of accompanying offspring into suitable areas not yet occupied or forcefully annexing part of an adjacent territory. Replacement of an adult by its offspring may also occur. A conclusion is that the probability of a young gibbon gaining a territory and mate is greater in the proximity of its parental group than in areas farther afield.

Evolution of long-distance alarm calls in Kloss's gibbon

WE present evidence here that proximity of close kin is a plausible hypothesis to explain the evolution of long-distance alarm calls in Kloss's gibbon (Hylobates klossii). We discovered two alarm calls produced by adults of this monogamous ape that provide good locational cues and are audible for much greater distances than required to signal the immediate family. Our further finding that at least some Kloss's gibbons settle in territories adjacent to their parental families when they mature and establish their own reproductive groups suggests that the adaptive significance of these calls is to warn neighbouring relatives of the presence and location of danger.