Gibbon Population Research Articles

How many remnant gibbon populations are left on Hainan? Testing the use of local ecological knowledge to detect cryptic threatened primates.

For Critically Endangered "species of extreme rarity," there is an urgent need to clarify the potential survival of remnant populations. Such populations can be difficult to detect using standard field methods. Local ecological knowledge (LEK) represents an important alternative source of information, but anecdotal reports of rare or possibly extinct species can contain uncertainty and error. The Hainan gibbon (Nomascus hainanus), the world's rarest primate species, is confirmed to only survive as a tiny remnant population in Bawangling National Nature Reserve, China, but unverified gibbon sightings have been reported from other forest areas on Hainan. We conducted a large-scale community interview survey to gather new data on patterns of primate LEK from 709 respondents around seven reserves across Hainan, to investigate the possibility of gibbon survival outside Bawangling and assess whether LEK can provide useful information for conservation management of cryptic remnant populations. Comparative LEK data for gibbons and macaques are consistent with independent data on the relative status of these species across Hainan. Local awareness and experience of gibbons was low across Hainan, including at Bawangling, but we recorded recent anecdotal gibbon reports from most reserves. A follow-up field survey at Limushan Provincial Nature Reserve did not detect gibbons, however, and documented intensive wildlife exploitation within this reserve. All other surveyed landscapes showed some statistically lower levels of respondent awareness, experience, or sighting histories of gibbons compared to Bawangling, and are therefore considered biologically unlikely to support gibbons. Unverified LEK data can provide important insights into the possible status of cryptic remnant populations when assessed carefully and critically in relation to data from known populations.

Population mapping of gibbons in Kalimantan, Indonesia: correlates of gibbon density and vegetation across the species’ range

The first comprehensive survey of gibbons (Hylobates spp.) across Indonesian Borneo was carried out over 3 years to (1) determine whether densities of gibbon species are cor- related with vegetation characteristics, and if so, whether the same characteristics are correlated with density across all forest types; and (2) determine population densities in the survey areas and identify threats to the areas. To achieve this, a total of 8 forest blocks were surveyed, involving 53 independent survey locations and repeat surveys in 3 forest blocks. Our data show that gibbons are ubiquitous where there is forest; however, the quality of forest affects population density, for- est block size affects longevity of populations, and populations are susceptible to the 'compression effect', i.e. populations occupy smaller fragments at unsustainably high densities. We show the effects of forest disturbance (logging, fire, fragmentation) on gibbon distribution and density and highlight issues for long-term conservation. We discuss the use of minimum cross-sectional area, habitat variables and presence of top foods to determine population density and to identify a threshold below which gibbons cannot persist. We discuss the conservation issues facing all Bornean gibbons, including natural hybrids (H. muelleri × H. albibarbis). The answers to these research questions will help mitigate threats to gibbons and their habitat, as well as identify key habitat for gibbon populations within and outside the protected area network.

An Efficient Acoustic Density Estimation Method with Human Detectors Applied to Gibbons in Cambodia.

Some animal species are hard to see but easy to hear. Standard visual methods for estimating population density for such species are often ineffective or inefficient, but methods based on passive acoustics show more promise. We develop spatially explicit capture-recapture (SECR) methods for territorial vocalising species, in which humans act as an acoustic detector array. We use SECR and estimated bearing data from a single-occasion acoustic survey of a gibbon population in northeastern Cambodia to estimate the density of calling groups. The properties of the estimator are assessed using a simulation study, in which a variety of survey designs are also investigated. We then present a new form of the SECR likelihood for multi-occasion data which accounts for the stochastic availability of animals. In the context of gibbon surveys this allows model-based estimation of the proportion of groups that produce territorial vocalisations on a given day, thereby enabling the density of groups, instead of the density of calling groups, to be estimated. We illustrate the performance of this new estimator by simulation. We show that it is possible to estimate density reliably from human acoustic detections of visually cryptic species using SECR methods. For gibbon surveys we also show that incorporating observers’ estimates of bearings to detected groups substantially improves estimator performance. Using the new form of the SECR likelihood we demonstrate that estimates of availability, in addition to population density and detection function parameters, can be obtained from multi-occasion data, and that the detection function parameters are not confounded with the availability parameter. This acoustic SECR method provides a means of obtaining reliable density estimates for territorial vocalising species. It is also efficient in terms of data requirements since since it only requires routine survey data. We anticipate that the low-tech field requirements will make this method an attractive option in many situations where populations can be surveyed acoustically by humans.

Effects of group density, hunting, and temperature on the singing patterns of eastern hoolock gibbons (Hoolock leuconedys) in Gaoligongshan, Southwest China.

Many non-human primates produce species-specific loud calls to communicate within and between groups over long distances. Understanding these calling patterns can provide insights into how individuals modify their behavior in response to environmental variables as well as help to design efficient bioacoustic survey techniques. Eastern hoolock gibbons in Gaoligongshan inhabit the coldest habitat of all gibbon populations, but both conservation and research efforts on this population have been minimal. We studied singing patterns of two habituated and two unhabituated groups at two sites in Gaoligongshan between July 2010 and June 2015. We systematically collected data of their calls, and its relationship to temperature, group density, and hunting pressure over at least 1 year for each group. Our goal was to elucidate how these factors affect singing patterns of eastern hoolock gibbons. We found that adult pairs coordinated their singing to produce duet bouts that lasted for an average of 25.5 min. The singing rate (number of bouts/number on monitoring days*100%: 7.5-31.4%) was notably lower than other gibbon populations, presumably due to low group density (about 0.5 groups/km(2) ) and prevalence of hunting at the study site. Cold temperature also affected gibbons' singing behavior. Our study groups called, on average, 2.5 hr after sunrise, probably foraging first in the early morning after long nights in this cold habitat delayed singing. Furthermore, mean temperatures in the morning (8:00-12:00 am) were higher on singing days than on non-singing days, and one group called less frequently when monthly mean temperature was below 10°C. Our findings indicate that both hunting pressure from humans and low temperatures suppress calling behavior in hoolock gibbons. Such information is critical in evaluating the use of duetting as a monitoring technique for this endangered gibbon species. Am. J. Primatol. 78:861-871, 2016. © 2016 Wiley Periodicals, Inc.

The past, present, and future of gibbons in China

Gibbons (Hylobatidae) were widely distributed across much of China during recent centuries, but are now restricted to a few small areas of Hainan, Guangxi, and Yunnan provinces due to massive habitat loss and hunting. Six gibbon species have occurred recently in China. Two of them (Hylobates lar and Nomascus leucogenys) are now extinct; two others (Nomascus nasutus and Nomascus hainanus) each have only one small population with less than 30 individuals; Hoolock leuconedys has a small population of less than 200 individuals distributed in 17 locations; and even the most common species, Nomascus concolor, has populations containing only about 270 social groups (ca. 1200 individuals). Illegal hunting, forest fragmentation, small population size, limited habitat, and various other types of human disturbance still threaten remnant gibbon populations. Currently, all gibbon species are listed as Class One Protected Animals by Chinese law and about 85% of gibbon groups are protected within nature reserves. Several long-term monitoring and research programs have been established in order to better understand gibbon population dynamics, ecology, and behavioral adaptations to human disturbance, and habitat restoration and conservation education programs are underway. In order to ensure long-term survival of gibbons in China, expanding and establishing nature reserves, strengthening law enforcement, increasing conservation education, establishing captive breeding programs for reintroduction, recruiting new researchers and students, and international cooperation are suggested. If most of these activities can be achieved, Chinese gibbons may still have a future in the wild.

Historical data as a baseline for conservation: reconstructing long-term faunal extinction dynamics in Late Imperial-modern China.

Extinction events typically represent extended processes of decline that cannot be reconstructed using short-term studies. Long-term archives are necessary to determine past baselines and the extent of human-caused biodiversity change, but the capacity of historical datasets to provide predictive power for conservation must be assessed within a robust analytical framework. Local Chinese gazetteers represent a more than 400-year country-level dataset containing abundant information on past environmental conditions and include extensive records of gibbons, which have a restricted present-day distribution but formerly occurred across much of China. Gibbons show pre-twentieth century range contraction, with significant fragmentation by the mid-eighteenth century and population loss escalating in the late nineteenth century. Isolated gibbon populations persisted for about 40 years before local extinction. Populations persisted for longer at higher elevations, and disappeared earlier from northern and eastern regions, with the biogeography of population loss consistent with the contagion model of range collapse in response to human demographic expansion spreading directionally across China. The long-term Chinese historical record can track extinction events and human interactions with the environment across much longer timescales than are usually addressed in ecology, contributing novel baselines for conservation and an increased understanding of extinction dynamics and species vulnerability or resilience to human pressures.

Habitat Characteristics and Their Effects on the Density of Groups of Western Hoolock Gibbon (Hoolock hoolock) in Namdapha National Park, Arunachal Pradesh, India

Understanding the relationship between a species and its habitat is crucial for conservation action planning. The Endangered western hoolock gibbon (Hoolock hoolock) has a fragmented distribution in northeast India, Bangladesh and parts of western Myanmar. Namdapha National Park in Arunachal Pradesh contains the largest population of western hoolock gibbons in India. We carried out an auditory sampling survey and habitat analysis of western hoolock gibbons in the park from September to December 2012 in three potentially suitable forest types: tropical broad-leaved forest, tropical wet evergreen forest, and wet temperate forest. A new method of analysis of singing frequency revealed that only 21–23% of groups sing per day. Group detectability declined sharply beyond a listening radius of 600 m. Auditory sampling across 15 listening areas revealed an estimated mean density of 3.65 groups km−2. We found no significant differences in density among forest types. The habitat study revealed a total of 122 species of trees (girth at breast height ≥30 cm) in the three forest types, representing 73 genera in 41 families, with the highest number of tree species in wet evergreen forest (93) followed by tropical broad-leaved forest (52) and wet temperate forest (40). None of the vegetation traits we measured (mean canopy cover, girth, density, and total basal area of all trees) and no habitat disturbance factors correlated significantly with gibbon density. This lack of correlation may have been due to the prevailing anthropogenic effects that adversely affected gibbons and their habitat, such as forest degradation, road widening, and hunting, overriding the relatively smaller natural variation in vegetation. This study adds to our knowledge of the habitat requirements of hoolock gibbons and indicates that Namdapha National Park is more important to conservation of the western hoolock than previously thought.

Gibbon (Hylobates lar) reintroduction success in Phuket, Thailand, and its conservation benefits.

We summarize the results from a long-term gibbon reintroduction project in Phuket, Thailand, and evaluate its benefits to conservation. Between October 2002 and November 2012, eight breeding families of white-handed gibbons (Hylobates lar) were returned to the wild in Khao Phra Thaew non-hunting area (KPT). Wild gibbons were extirpated from Phuket Island by the early 1980s, but the illegal wildlife trade has continued to bring young gibbons from elsewhere to the island's popular tourist areas as pets and photo props. The Gibbon Rehabilitation Project (GRP) has rescued and rehabilitated confiscated and donated captive gibbons since 1992 and aims to repopulate the island's last sizable forest area. Following unsuccessful early attempts at translocation in the 1990s, GRP has now developed specific methods for gibbon reintroduction that have led to the establishment of a small independent, reproducing population of captive-raised and wild-born gibbons on Phuket. Eleven infants have been born wild within the reintroduced population, including a second generation wild-born gibbon in September 2012. Benefits of the GRP project include restoration of the gibbon population on Phuket, rescue of illegally kept gibbons, public education, training of personnel in gibbon conservation work, and gaining experience which may prove useful in saving more severely threatened species. It is unlikely that gibbon (and other large primate) translocations will make a significant contribution to conservation of the species as a whole, and primate translocation projects should not be judged solely by this criterion.

Understanding stable bi-female grouping in gibbons: feeding competition and reproductive success.

IntroductionSpecies of the order Primates are highly gregarious with most species living in permanent heterosexual social groups. According to theory in socioecology maximum social group size is limited by rates of intra-group feeding competition and associated increases in travel costs. Unlike other hylobatids, which are predominantly pair living, cao vit gibbons (Nomascus nasutus), and two other species of crested gibbon (Nomascus spp.) living in northern seasonal forest, regularly exhibit larger bi-female groups. To better understand the ability of northern gibbons to live in stable bi-female groups, we examined food distribution, feeding competition and reproductive success over a period of six years in a small cao vit gibbon population at Bangliang, Guangxi, China.ResultsIn general, we found weak evidences for within-group contest or scramble competition in our two study groups, which we attribute to high spatial and temporal heterogeneity in the distribution of their important food species. Nevertheless, the larger of the two groups studied increased feeding time and group spread during lean periods, factors that may limit cao vit gibbon group size to a maximum of two breeding females. Relative to tropical pair-living gibbons, there is no evidence that cao vit gibbons travel farther or spend more time feeding, but they did consume more leaves and buds and less fruit and figs. Despite their highly folivorous diet, the average inter-birth interval is comparable to tropical gibbon populations, and the survival rate of infants and juveniles in our study groups is high.ConclusionCao vit gibbons do not suffer obvious costs in terms of feeding competition and reproductive success by living in bi-female groups, but within-group feeding competition may determine the upper the limit of cao vit gibbon group size to a maximum of two breeding females. These findings contribute to a growing body of evidence that bi-female grouping can be a stable grouping pattern of gibbons in certain habitats and further emphasize the flexibility of gibbon social organization.

テナガザル 2種（<i>Hylobates lar</i>，<i>Hylobates pileatus</i>）の Y染色体多型マーカーの確立

Genet ic assessment of gibbon populations is required to establish and develop the conservation management of endangered gibbon species. To assess the paternal genetic diversity of wild gibbons, we searched and developed six loci of the Y-chromosomal marker that consist of five microsatellites and three PCR fragment length polymorphisms in two species of gibbons, Hylobates lar (white-handed gibbons) and H. pileatus (pileated gibbons). Using these Y-chromosomal markers, no individual shared a Y-chromosomal haplotype with any other individual among captive H. lar (n = 12) and H. pileatus (n = 5). The application of the Y-chromosomal markers developed in this study will help us to uncover the genetic diversity of these two gibbon species.

Habitat use and Documentation of a Historic Decline of Western Hoolock Gibbon (Hoolock hoolock) in Dampa Tiger Reserve, Mizoram, India

The western hoolock gibbon Hoolock hoolock is globally threatened because of a combination of habitat loss, frag- mentation and hunting. Most remaining populations are isolated and contain few individuals. We studied a small population of western hoolock gibbons in Dampa Tiger Reserve in Mizoram, India, an area with a deep-rooted tradition of hunting wildlife. We quantified differences in 35-ha sites that were used by gibbons (n = 9) with those that were not (n = 6). We found no statistical differences with respect to canopy continuity, distance to the nearest village or levels of habitat disturbance, but were not able to quantify levels of hunting. Interviews with local villagers (n = 53) from seven villages distributed throughout the reserve suggests that gibbon numbers declined progressively from the early 1970s to the present day, possibly from >100 to <50 individuals. Inter- viewees pointed at the combined result of fire (from, for instance, slash-and-burn cultivation), reduction of the available habitat, and hunting, exacerbated by an increase in the human population, as possible causes. This corresponds well with our analysis of vegetation maps of the reserve based on satellite imagery, that show a decline in suitable habitat from 63% of the reserve in 1978, to 59% in 1989, and 50% in 2005. We strongly recommend a greater emphasis on quantifying the impacts of hunting on the distribution and persistence of hoolock gibbons.

Dietary variability in the western black crested gibbon (Nomascus concolor) inhabiting an isolated and disturbed forest fragment in Southern Yunnan, China

Forest fragmentation and isolation can reduce the size of available habitat and lead to lower food availability for some primate species. The persistence of nonhuman primates in fragments depends largely on their ability to adjust their diet in response environmental change. The western black crested gibbon (Nomascus concolor) is distributed in northern Vietnam, northwestern Laos, and southwestern China, but little is known about its diet except from studies in the well-protected forests of Mt. Wuliang and Mt. Ailao, central Yunnan. We studied food abundance and diet over 2 years in a small group surviving in an isolated and disturbed forest at Bajiaohe, southern Yunnan, and drew a comparison with the population at Dazhaizi in Mt. Wuliang. We found that gibbons at Bajiaohe consumed mostly fruit, but did not eat figs, unlike most other gibbon populations. Liana fruits and mature leaves were used as alternative foods during periods of tree fruit scarcity. Our results indicate that gibbons in Bajiaohe respond to habitat fragmentation and isolation by consuming a variety of plant species, depending on those that are locally available, and increasing time spent feeding on fruits of trees and lianas rather than increasing time spent consuming leaves.

Habitat evaluation and population viability analysis of the last population of cao vit gibbon (Nomascus nasutus): Implications for conservation

The cao vit gibbon (Nomascus nasutus) is among the most endangered primates in the world. The only surviving population lives in a karst forest patch along the China–Vietnam border. In this study, we used high-resolution satellite images to evaluate the habitat quality of the gibbon in the area immediately surrounding the last population and predict the potential gibbon habitat. We then used Vortex to simulate population responses to changes in the habitat’s carrying capacity. Our results showed the gibbon population is approaching the carrying capacity of their current habitat, and carrying capacity has a significant impact on population changes. Two potential habitats were located in a forest connected to the current habitat by a narrow forest corridor, situated above an underground river. Based on the results, we recommend: (1) prohibiting agriculture and grazing activities within the current gibbon habitat; (2) expanding the Cao Vit Gibbon Conservation Area in order to protect potential cao vit habitats in Vietnam; (3) protecting forest corridor that connect the current cao vit habitat to potential habitats; and (4) rehabilitating the forests currently depauperate of important food species in order to support the expansion of both the gibbon population and the range. This research both provides important insight into sustaining the current gibbon population as well as suggestions for both Vietnamese and Chinese local governments planning habitat restoration at the study site.

Habitat characterization of western hoolock gibbons Hoolock hoolock by examining home range microhabitat use

Conserving a species depends on an understanding of its habitat requirements. Primatologists often characterize the habitat requirements of primates using macroscale population-based approaches relying on correlations between habitat attributes and population abundances between sites with varying levels of disturbance. This approach only works for species spread between several populations. The populations of some primates do not fulfill these criteria, forcing researchers to rely on individual-based (microscale) rather than population-based approaches for habitat characterization. We examined the reliability of using micro-scale habitat characterizations by studying the microhabitat preferences of a group of wild western hoolock gibbons (Hoolock hoolock) in order to compare our results to the habitat preferences of western hoolock gibbons identified during a macroscale study of populations across Bangladesh. We used stepwise discriminant analysis to differentiate between the areas of low, medium, and high usage based on microhabitat characteristics (tree species availability, altitude, canopy connection, distance from forest edge, and levels of human disturbance). The gibbons used interior forest habitat with low food tree availability most frequently for sleeping and socializing, and used edge habitat containing high food tree availability for medium periods for feeding. These results indicate that the gibbons prefer interior forest but are frequently forced to visit the forest edge to feed. Therefore, the optimal habitat would be interior forest away from human disturbance with high sleeping-tree and feeding-tree availability. These habitat preferences are consistent with the habitat attributes of Bangladesh's largest remaining western hoolock gibbon populations, which live in areas containing low agricultural encroachment and high food-tree availability. Microhabitat use studies can be used to characterize the habitat requirements of a species, but should include multiple scales of analysis wherever possible.

Effects of social status and stress on patterns of gastrointestinal parasitism in wild white‐handed gibbons (Hylobates lar)

Although gibbons (family Hylobatidae) are typically monogamous, polyandrous groups occur regularly. Stress associated with elevated intragroup competition among males in polyandrous groups may increase susceptibility to infectious disease. To better understand this interplay, as well as to provide the first comprehensive assessment of parasitism in free-ranging gibbons, we characterized the richness of gastrointestinal parasites and examined their prevalence in males from 14 groups (10 pair-living, 4 multi-male) of white-handed gibbons (Hylobates lar) at Khao Yai National Park, Thailand. From September 2008 to May 2009, 324 fecal samples were collected from 23 individually recognizable male gibbons and screened for gastrointestinal helminths and protozoa after isolation via fecal floatation, sedimentation, and immunofluorescent antibody detection. A total of 10 parasite species recovered, including seven nematodes, two protozoans, and one trematode. Parasite richness and species-specific prevalence were examined relative to social organization (pair-living vs. multi-male), male status (primary vs. secondary), age (subadult, adult, senior), fecal glucocorticoid levels, and time of the year. No relationship was found between parasite richness and sociodemographic or physiological factors. Similarly, prevalence of infection with parasite species was not associated with the majority of sociodemographic factors; however, Ternidens sp. and Balantidium coli varied seasonally and Trichuris sp. decreased with increasing age. Moreover, observational data suggest that competition is low in this gibbon population, and our findings are consistent with those observations in that cooperative defense may offset stress and reduce susceptibility to infection.

Seasonal variation of diet and time budget of Eastern hoolock gibbons (Hoolock leuconedys) living in a northern montane forest

Most gibbons dwell in the tropical forests of Southeastern Asia, but eastern hoolock gibbons (Hoolock leuconedys) survive in high montane forest ranging from 1,600 to 2,700m a.s.l. in Gaoligongshan (>24°30'N), Yunnan, China. To assess the behavioral adaptations of hoolock gibbons to the montane forest, we related temperature and food availability within the habitat to the seasonal behavioral patterns of a family group and a solitary female between August 2010 and September 2011 in Nankang, Gaoligongshan National Nature Reserve. The maximum temperature was 29.2°C and the minimum temperature was -0.3°C during the period. The monthly mean temperature was <10°C between December and February, making Nankang the coldest gibbon habitat reported so far. Nonfig fruit and fig availability declined to nearly zero in cold months. The family group increased resting and decreased travel and social behaviors when the monthly mean temperature was low. Compared with other gibbon populations, the hoolock gibbons spent proportionally less time feeding on figs and other fruit than other gibbon populations except Nomascus concolor and Symphalangus syndactylus. Only 36 species of plants provided nonfig fruit or figs, which is less than the number of fruit species consumed by any other gibbon population observed during a similar period of time (about 1year). Hoolock gibbons shifted their diet to leaves and increased feeding time when fruit was not available. We conclude that diet flexibility and an energy-conserving strategy during the cold season when fruit is scarce have enabled the hoolock gibbons to survive in a northern montane forest.

Population and distribution of western black crested gibbon (Nomascus concolor) at Ailao Mountain, Xinping, Yunnan

The western black crested gibbon (Nomascus concolor) is mainly distributed in Yunnan, China. Ailao Mountain is located in central Yunnan and divided into three prefectures and six counties. This mountain forms the principle distribution range for western black crested gibbon; however, there are no published data on the gibbon population inhabiting the Xinping administrative. Take the interview results conducted in 2007 and 2009 with local people as the reference, this study conducted an extensive field survey covering all possible habitats from November 2009 to January 2010 using call surveys. Among the one hundred and twenty-four gibbon groups which were confirmed across the Ailao Mountain, the largest known population of western black crested gibbons yet, 85 groups inhabit the national nature reserve and adjacent national forest, 30 groups inhabit the provincial nature reserve and nine groups inhabit the collective forest located outside the reserve and national forest. We found that the western black crested gibbons here have a patchy distribution pattern and occur at higher densities in certain areas. Moreover, the population distribution density and elevation gradient distribution decline from north to south. The results also demonstrated the importance of Ailao Mountain in the western black crested gibbon protection.

Demography of Agile Gibbons (Hylobates agilis) in a Lowland Tropical Rain Forest of Southern Sumatra, Indonesia: Problems in Paradise

Gibbons are among the best-studied Asian primates, but few studies address their demography and life history strategies. We used annual censuses to study the demography of agile gibbons (Hylobates agilis) between 1998 and 2009 in rain forests of Bukit Barisan Selatan National Park, Indonesia. The population declined from 22 individuals (9 groups) to 14 individuals (5 groups) over the 12 yr of study. Infant survival to the juvenile age class was 33.3%, and 16.7% of infants survived to the subadult age class. The interbirth interval was 3.83±1.15 yr and birth rate was 0.22-0.28 infants female -1 yr -1 . Two groups colonized the study area but subsequently disappeared. We documented 7 immigrations, 17 disappearances, and ≥10 transients in the population. Compared to lar gibbons (Hylobates lar) and Bornean white-bearded gibbons (Hylobates albibarbis), Way Canguk's agile gibbon population is characterized by slow reproduction, low survival, and high group turnover. We hypothesize that, although the habitat is high in fruit resources, agile gibbons may be displaced or excluded from the best fruit resources by larger and more numerous competitors, incurring costs of decreased opportunities to forage and increased travel, and leading to higher mortality for young agile gibbons. The reproductive potential of this agile gibbon population is insufficient to compensate for high mortality, and the population is unlikely to persist without immigration from outside the area. Given the agile gibbons' endangered status and limited capacity to respond demographically to change, it is likely that intensive management interventions will be required to conserve this species.

Ex situ gibbon conservation: status, management and birth sex ratios

Many zoos take part in captive‐management programmes for gibbon species, which contribute to the conservation of this highly threatened taxon. Eight gibbon species are represented in captive‐management programmes globally, although the numbers held are highly biased towards only two species, which fill most of the space available in zoos. The other gibbon species are held in small populations that are difficult to manage and, thus, are unlikely in their current form to be self‐sustaining. Effort and, more importantly, space are required to grow these small gibbon populations. In addition, the space that is available needs to be used wisely. This may require that only animals that can actively contribute, whether genetically or socially, to the goal of achieving a self‐sustaining captive population are maintained. There is also a need to investigate the impact of environmental factors in captivity as they relate to birth and death rates, which would enable evidence‐based captive management of gibbons with the aim of stimulating breeding and mitigating the potential deleterious impacts associated with managing small populations.

Current status of Western Hoolock Gibbon Hoolock hoolock Harlan in West Garo Hills, Meghalaya, India

A rapid status survey of Hoolock Gibbon was carried out in 28 localities of West Garo Hills, Meghalaya in March-April 2007. These 28 were among the 32 localities surveyed previously during 1985-1987 by Alfred & Sati (1990). Gibbons were found in only 15 of the 28 localities. Only 25 groups of gibbon totaling 82 individuals were observed, compared to 36 groups with 111 individuals recorded at the same sites 20 years ago. Adults comprised nearly 61% of the total individuals, followed by infants 16%, juveniles 13% and sub-adults 10%. While the proportion in the adult age class had decreased from 67% in 1985-87, the proportion of individuals in all other age classes showed slight increase. The sex ratio of males: females was 1:1 for adults as well as sub-adults, which was the same as in 1985-87 survey. The modal group size was three (44% of groups) as before. However, the next frequent group size was four (28% of groups), whereas previously the second most frequent group size was two (30% of groups). Twenty percent of groups had two individuals and 8% of groups comprised of five individuals. The Hoolock Gibbon population in the West Garo Hills showed a decreasing trend of 26.2% (82 individuals out of 111 individuals) in 28 localities, when compared with the previously documented numbers. The major reasons of their decline are anthropogenic disturbances such as tree felling for domestic and commercial uses; intermittent cutting of new forest patches for fresh jhum cultivation, often resulting into canopy gaps as well as habitat loss; livestock grazing and poaching.