Nomascus Concolor Research Articles

Recognition of Western Black-Crested Gibbon Call Signatures Based on SA_DenseNet-LSTM-Attention Network

As part of the ecosystem, the western black-crested gibbon (Nomascus concolor) is important for ecological sustainability. Calls are an important means of communication for gibbons, so accurately recognizing and categorizing gibbon calls is important for their population monitoring and conservation. Since a large amount of sound data will be generated in the process of acoustic monitoring, it will take a lot of time to recognize the gibbon calls manually, so this paper proposes a western black-crested gibbon call recognition network based on SA_DenseNet-LSTM-Attention. First, to address the lack of datasets, this paper explores 10 different data extension methods to process all the datasets, and then converts all the sound data into Mel spectrograms for model input. After the test, it is concluded that WaveGAN audio data augmentation method obtains the highest accuracy in improving the classification accuracy of all models in the paper. Then, the method of fusion of DenseNet-extracted features and LSTM-extracted temporal features using PCA principal component analysis is proposed to address the problem of the low accuracy of call recognition, and finally, the SA_DenseNet-LSTM-Attention western black-crested gibbon call recognition network proposed in this paper is used for recognition training. In order to verify the effectiveness of the feature fusion method proposed in this paper, we classified 13 different types of sounds and compared several different networks, and finally, the accuracy of the VGG16 model improved by 2.0%, the accuracy of the Xception model improved by 1.8%, the accuracy of the MobileNet model improved by 2.5%, and the accuracy of the DenseNet network model improved by 2.3%. Compared to other classical chirp recognition networks, our proposed network obtained the highest accuracy of 98.2%, and the convergence of our model is better than all the compared models. Our experiments have demonstrated that the deep learning-based call recognition method can provide better technical support for monitoring western black-crested gibbon populations.

Vocal differences in note, sequence and great call sequence among three closely related Nomascus gibbon species

AbstractThe vocal structure of gibbons has long been believed to be under strong genetic control and consistent with phylogeny. Gibbon vocalizations show hierarchical structures and song coordination behaviors, which may have different functions and convey distinct information compared to basic notes. However, previous studies have not compared vocalizations at multiple levels across species. We compared the vocal structures of three Nomascus species in the wild in South China, namely the western black gibbon (Nomascus concolor), Cao vit gibbon (N. nasutus), and Hainan gibbon (N. hainanus) at the levels of note (six features of four types of notes), male sequence (eight features), and song coordination (four features of the overlap pattern between male and female songs). We selected 15 recordings for each species: N. concolor (six groups, 2006 to 2021), N. nasutus (seven groups, 2008 to 2021), and N. hainanus (six groups, 2020 to 2021). We used permuted random forest analysis to test for species differences in vocal structure and the contribution of acoustic features to species differences at each level. We used acoustic features to construct a hierarchical clustering tree, and compared it with phylogenetic relationships. We found significant differences at all levels except the boom note. Acoustic similarity did not match genetic similarity in boom and pre-modulated notes, suggesting that genetic differences are not the only factor leading to species differences in vocal structures. We also found different contributions of acoustic features to differentiation in vocal structure at different levels. Our study suggests that we need to compare gibbon vocalizations at different levels to understand their differentiation and evolution.

Landscape and conservation genetics of western black crested gibbons (Nomascus concolor) in China.

Despite decades of field study, very little is known about the molecular ecology of gibbons, particularly as it relates to their ability to disperse across degraded and fragmentary landscapes. The critically endangered western black crested gibbon (Nomascus concolor) has been reduced to a small, fragmented population with about 1300 individuals. In the largest population genetic study of free-ranging gibbons to date, we sampled 47 of these gibbons from 13 sites in China and generated 15 polymorphic autosomal microsatellite markers. We identify three population clusters of N. concolor in Yunnan centered in 1) the Wuliang and Ailao Mountains, 2) the Yongde Daxueshan Mountains, and 3) an isolated remnant near the border with Vietnam. Within the Wuliang Mountains, we identified four subclusters, three of which are bounded by high-altitude rhododendron forest, and one that is isolated from the main population by ~2 km of degraded forest and pasture. Least-cost path analysis and isolation by resistance modeling demonstrates that the population genetic distances among gibbons in Wuliangshan National Nature Reserve are significantly correlated with geographic paths that avoid use of high-altitude rhododendron forest in favor of evergreen broadleaf forest. Although these gibbons have likely undergone reductions in heterozygosity from recent consanguineous mating, we suggest that their active avoidance of inbreeding on the population level maintains higher than expected levels of genetic diversity. This research provides new insights into how gibbons interact with heterogeneous environments and expands our understanding of their molecular ecology and conservation genetics.

Stable habitat supports long-term persistence of critically endangered western black crested gibbon

Stable habitat provides sufficient food to sustain large species populations, and becomes a refuge under increasing environmental stress. Stable habitat also becomes a population source and re-expand hotspot once the stress decreases. Thus, identifying and protecting stable habitat is key to species’ long-term persistence. We identified the stable habitat for critically endangered western black crested gibbon (Nomascus concolor) in Mt. Wuliang, where one of two largest populations of this species lives in. We collected gibbon historical distribution data, and modeled the potential habitat in Mt. Wuliang during 2000, 2010, and 2020. We identified the stable habitat by overlaying the potential habitat layers from the three time periods and excluded habitat patches smaller than the species’ home range. Gibbon habitats continuously expanded from 2000 to 2010 (+13%), and from 2010 to 2020 (+6%), indicating that gibbon habitats are recovering at Mt. Wuliang. Stable habitat was 304 km2, mainly located at mid-elevation (2 100 – 2 600 m). Nearly all (99%) gibbon groups occupied stable habitat in each period at a mean density of 0.34 groups/ km2. Gibbon population density in the Wuliangshan National Nature Reserve (WNNR, 0.44 groups/ km2) was 83% greater than that density outside WNNR (0.24 groups/ km2). However, only 50% of stable habitat was within WNNR. Thirteen stable habitat patches located outside WNNR require urgent conservation interventions. Stable habitat in protected area is sufficient to ensure the persistence of these gibbons, but we still need to involve stable habitat outside protected area to sustain population recovery in the future.

Methods for processing and analyzing passive acoustic monitoring data: An example of song recognition in western black-crested gibbons

The extraction of species-specific calls from passive acoustic recordings is a common preliminary step in ecological analysis. But for many species, especially those occupying noisy, acoustically variable habitats, the call extraction process remains largely manual, a time-consuming, and increasingly unsustainable process. Deep neural networks have been shown to provide excellent performance in a range of acoustic classification applications. We take as an example the recognition of four songs of one of the rarest mammals in the world, the western black-crested gibbon (Nomascus concolors).The process of recognition in this paper which includes distributed BIC ambient sound segmentation based on the OpenPAI platform; DNN-based western black-crested gibbon song enhancement processing; data pre-processing, labeling samples; proposed DNN + ResNet34 + CBAM + GRU + Attention recognition model; comparing other classical neural network models.Our best model converts acoustic recordings into spectrogram images on the mel frequency scale and uses these images to train convolutional neural networks.Our proposed model proved to be very accurate in predicting the segmented western black-crested gibbon songs with an accuracy of 99.8%, and almost a few western black-crested gibbon songs were incorrectly identified when all segmented data were recognized. In the four consecutive years of the acoustic monitoring system deployed in the Ailao Mountain National Nature Reserve, the western black-crested gibbon was most active near the monitoring site from March to August each year, and least active in January and February. Based on call sound intensity analysis, we monitored a total of two different western black-crested gibbon groups (G1 and G2) during the monitoring cycle. We demonstrate that passive acoustic monitoring combined with CNN classifiers is an effective tool for the remote detection of one of the rarest and most threatened species in the world.

Sympatric primate seed dispersers and predators jointly contribute to plant diversity in a subtropical forest.

Mutualistic and antagonistic plant-animal interactions differentially contribute to the maintenance of species diversity in ecological communities. Although both seed dispersal and predation by fruit-eating animals are recognized as important drivers of plant population dynamics, the mechanisms underlying how seed dispersers and predators jointly affect plant diversity remain largely unexplored. Based on mediating roles of seed size and species abundance, we investigated the effects of seed dispersal and predation by two sympatric primates (Nomascus concolor and Trachypithecus crepusculus) on local plant recruitment in a subtropical forest of China. Over a 26month period, we confirmed that these primates were functionally distinct: gibbons were legitimate seed dispersers who dispersed seeds of 44 plant species, while langurs were primarily seed predators who destroyed seeds of 48 plant species. Gibbons dispersed medium-seeded species more effectively than small- and large-seeded species, and dispersed more seeds of rare species than common and dominant species. Langurs showed a similar predation rate across different sizes of seeds, but destroyed a large number of seeds from common species. Due to gut passage effects, gibbons significantly shortened the duration of seed germination for 58% of the dispersed species; however, for 54% of species, seed germination rates were reduced significantly. Our study underlined the contrasting contributions of two primate species to local plant recruitment processes. By dispersing rare species and destroying the seeds of common species, both primates might jointly maintain plant species diversity. To maintain healthy ecosystems, the conservation of mammals that play critical functional roles needs to receive further attention.

Experimental evidence for nasty neighbour effect in western black crested gibbons (Nomascus concolor)

Experimental evidence for nasty neighbour effect in western black crested gibbons (Nomascus concolor)

Disassociation of social and sexual partner relationships in a gibbon population with stable one‐male two‐female groups

Adult males living in a one-male multi-female social group are expected to try to monopolize copulations with resident females to increase reproductive fitness. Gibbons have traditionally been described as living in monogamous groups, with the sole resident adult male assumed to sire all of the group's offspring. Here, we used microsatellite analyses and behavioral observations to examine rates of extra-group paternity (EGP) over 16 years in a population of crested gibbons (Nomascus concolor) that form stable and long-term one-male two-female social units. Forty percent of offspring (N = 14) were sired by extra-group males. To understand this high level of EGP, we tested whether inbreeding avoidance was related to EGP. Females who engaged in EGP did not show larger pairwise relatedness with their resident male compared to females who did not engage in EGP. Nevertheless, the standardized heterozygosity of EGP offspring was significantly higher than for offspring sired by the group's resident male. These results provide partial support for the inbreeding avoidance hypothesis. It appears that resident male crested gibbons are unable to monopolize resident females' matings. Our results indicate that long-term social partners are often distinct from sexual partners in this population. Clearly, the breeding system of crested gibbons is more flexible than previously thought, indicating a need for integrating long-term behavioral data and genetic research to re-evaluate gibbon social and sexual relationships derived from concepts of monogamy and pair-bonding.

Application of a combined model simulation to determine ecological corridors for western black-crested gibbons in the Hengduan Mountains, China

Habitat fragmentation is a critical contributor to biodiversity degradation and species extinction, as illustrated by the severely fragmented habitat of the western black-crested gibbon (Nomascus concolor), a critically endangered species in the Hengduan Mountains, China. An integrated simulation model, including the random forest algorithm (RFA), empirical bayesian kriging regression (EBKR), and the least-cost path model (LCP), is introduced to determine ecological corridors for western black-crested gibbons in the Hengduan Mountains. In this study, we identified habitat variables and movement behaviors of western black-crested gibbons through RFA and then proposed EBKR, which is combined with LCP to determine potential corridors. Model simulation results suggest that the western black-crested gibbons' habitat is mostly dependent on forests with an altitude of about 2,000 m and a 20° slope, areas undisturbed by human activities. Two land use and cover classes predominate inside the corridors, tree cover and mostly natural vegetation, corresponding to 67.55% and 18.54% of total land use, respectively. A total of nine corridors were planned in Hengduan Mountains via LCP. The shortest corridor, which has recently been incorporated into national park planning, is 7.40 km, and is a route that has no need for bridge construction. The longest corridor is 95.74 km and would require construction of three bridges. Mobility of western black-crested gibbons can increase by 39.49% using our simulated corridors. The planned corridor is an optimized route for western black-crested gibbons in the Hengduan Mountains, and provides the best opportunities for security, food, and survival. The proposed integrated model is an efficient method for designing and estimating habitat suitability using competitively predictive performance and simultaneously quantifying model uncertainties.

The character of parietal and orbital alterations in the superfamily Hominoidea (families Hominidae [exclusive of Homo] and Hylobotidae).

Parietal external surface disruption routinely referred to as porotic hyperostosis, and orbital alterations (cribra orbitalia), have been attributed to anemia-related bone marrow hyperplasia in humans. A recent study in humans identified that they were actually vascular in nature. Skeletons were examined and epi-illumination surface microscopy was performed on the parietal region and orbit of 156 Hominidae and 123 Hylobotidae to assess if these phenomena were trans-phylogenetic. Trans-cortical channels were recognized on the basis of visualized ectocranial surface defects penetrating the parietal; cribra orbitalia, by alteration of the normally smooth orbital roof appearance. Trans-cortical parietal channels, ranging in size from 20 to 100 µm, are rare in Gorilla and Pan troglodytes and absent in Pan paniscus. They are universally present in adult Pongo abeli and in Hylobatidae, independent of species. Cribra orbitalia was common in Hylobotidae, Pongo pygmaeus and P. abelii, less prevalent in adult P. troglodytes, and not recognized in any Gorilla gorilla or P. paniscus examined. The proliferative form predominated, with the exception of Hylobates concolor and muelleri, in which uncalcified vascular grooves predominated. No correlation was observed between the presence of either trans-cortical channels or cribra orbitalia and fractures, osteoarthritis, or inflammatory arthritis. Parietal alterations observed in apes are trans-cortical channels, analogous to those observed in humans, and do not represent porosity. Similarly, cribra orbitalia in apes is confirmed as vascular in nature. The proliferative form apparently represents calcification of blood vessel walls, indistinguishable from observations in humans. Predominant presence in adults rather than in juveniles suggests that both forms are acquired rather than developmental in derivation. Sex and bone alteration/disease-independence suggests that mechanical, endocrine, and inflammatory phenomena do not contribute to the development of either. Further, independent occurrence of trans-cortical channels and cribra orbitalia suggests that they do not have a shared etiology.

Asymmetric competition between sympatric endangered primates affects their population recovery

Species interactions including predation, competition, and parasitism, matter to species conservation. Sympatric species can have a profound influence on the population recovery of endangered species through a number of ecological processes, but particularly feeding competition. We investigated ranging (spatial pattern) and feeding (trophic overlap) behavior of sympatric critically endangered western black crested gibbons (Nomascus concolor) and endangered Indochinese gray langurs (Trachypithecus crepusculus). Our 1-year study of one group of each species found potential for asymmetric feeding competition between langurs and gibbons on Mt. Wuliang, China, in that: (1) the home range (2 km2) of the gibbon group was nearly entirely within the home range of the langur group (4.2 km2); (2) langurs had a greater niche breadth than gibbons, and their trophic overlap was 0.23; (3) 14 out of 26 primary food items comprising 56.7% of gibbon annual diet were consumed by langurs; and (4) langurs routinely consumed unripe fruits before they ripened sufficiently for gibbons to eat. Differences in group size, feeding habits, and reproductive rate could increase the effects of asymmetric dietary in potential competition, which appears to limit population recovery of gibbons. Rapid recovery of one species may cause unintended conservation consequences through complex interspecific interaction. Thus, it is important that conservation strategies take species interactions into account when designing conservation interventions. To ensure the ongoing survival of gibbons it may be necessary to manage langur populations.

Male gibbon loud morning calls conform to Zipf's law of brevity and Menzerath's law: insights into the origin of human language

The study of vocal communication in nonhuman primates, especially apes, offers critical insight into the origins of human language. Although human language represents a highly derived and complex form of communication, researchers have found that the organization of language follows a series of common statistical patterns, known as ‘linguistic laws’. Zipf's law of brevity and Menzerath's law are pervasive across human languages, and these laws have been identified in the communication of a small number of primate species. What remains less clear is whether these two laws also affect long-distance vocal communication in primates. Here, we provide evidence that the long-distance morning calls of male gibbons (cao vit gibbon, Nomascus nasutus, and western black-crested gibbon, Nomascus concolor ) follow both Zipf's law of brevity and Menzerath's law. We found that notes of male gibbon calls conform to Zipf's law of brevity, with the most common notes being shortest in duration. Similarly, longer sequences are made up of shorter calls on average, consistent with Menzerath's law; we also found a shortening of specific note type duration and an increase in proportion of shorter call types in longer sequences, which may underpin the emergence of this law. Our findings support the generality of these two linguistic laws beyond human language and provide evidence for compression at two levels of organizations (how frequently different note types are used, and how vocal sequences are constructed) in a long-range communication system. • Male gibbon morning calls conform to Zipf's law of brevity and Menzerath's law. • The most common notes being shortest in duration. • Longer sequences are made up of shorter calls on average.

The effective use of camera traps to document the northernmost distribution of the western black crested gibbon in China.

Gibbons represent a highly successful radiation of four genera and 20 species of Asian apes that, in response to recent habitat fragmentation and deforestation, are threatened with extinction. China has six species of gibbons, each of which is critically endangered. We present new biogeographical information on the distribution of the black crested gibbon (Nomascus concolor). Four subspecies of N. concolor have been described: three of them are present east of the Mekong River (Nomascus concolor jingdongensis, N. c. concolor and N. c. lu); and another is found west of the Mekong River (N. c. furvogaster). In addition, there has been speculation that gibbons exist in the Biluo Snow Mountains, between the Mekong and Salween basins. To clarify the biogeography of this species, from April 2011 to January 2012 and from January 2016 to September 2018, we conducted interviews with local villagers, completed line transect surveys, monitored gibbon calls, and placed 30 camera traps in the forest canopy. On October 30, 2016, we recorded gibbon's calls. On July 5, 2016, our camera traps obtained one image of a male gibbon, and on February 1 and 8, 2017, we captured two independent images of an adult female gibbon on Zhiben Mountains. Based on the black crest on the head, clearly visible in the photographs, the gibbons are N. c. furvogaster. Evidence from interviews and survey records indicate that N. c. furvogaster once was present in the Zhiben Mountains, at an altitude of between 2000 and 2700m. Between 1990 and 2000, some 6-7 groups still existed in Caojian, Laowo and adjacent areas. Unfortunately, in the absence of an effective conservation strategy, the population was extirpated by hunters. The remaining forest in the Zhiben Mountains is highly fragmented, and most of the suitable habitat for gibbons has been lost. Therefore, we expect that this newly found gibbon population is under extreme anthropogenic pressure. It is imperative that further investigations of this gibbon population be conducted immediately, and that the local and national governments implement effective conservation plans, including educating the local communities to protect this critically endangered primate population.

Influence of food availability and climate on behavior patterns of western black crested gibbons (Nomascus concolor) at Mt. Wuliang, Yunnan, China.

Food abundance and climatic factors can significantly affect the behavior of animals and constrain their activity budgets. The population of western black crested gibbons (Nomascus concolor) in Mt. Wuliang lives in montane forest and is close to the northern extreme of the distribution for gibbons (Hylobatidae). Their habitats show remarkable seasonal variation in terms of food availability, temperature, and rainfall. To understand behavioral adaptations of western black crested gibbons to different sets of ecological conditions, we examined relationships among food availability, mean temperature, rainfall, and behavior patterns by observing two groups for 1 year each. Our results revealed that activity budget was affected by food availability and mean temperature. The gibbons spent more time eating flowers when that resource was more available and spent less time moving when fruit was more available. The gibbons spent less time feeding and more time resting, and spent less feeding time on fruit and leaves when the mean temperature was lower. These results suggest that the gibbons displayed a pronounced preference for flowers as a food resource and adopted a time minimizer strategy when high-nutrient food items (i.e., fruit) were more available. In addition, the gibbons adopted an energy-conserving strategy during periods of low temperature. The flexibility of behavioral patterns in responding to food availability and temperature may potentially improve the gibbons' prospects of surviving and reproducing in a northern montane forest.

An Application of Autonomous Recorders for Gibbon Monitoring

Population monitoring is very important in wildlife management and conservation. All 18 species of gibbons are considered threatened with extinction and listed on the IUCN Red List of Threatened Species. Thus, understanding and effectively monitoring their population trends and distribution are critical. Thus far, all gibbon surveying and monitoring programs have been conducted by human surveyors; this is expensive, laborious, and dependent on the surveyors’ skills. In particular, estimating group density often requires a large sample size with several skilled observers working simultaneously in the field. We used autonomous recorders to record the calls of southern yellow-cheeked crested gibbon (Nomascus gabbrielae) for at least 3 days at each of 57 posts in Nam Cat Tien sector, Cat Tien National Park, Vietnam from July to October, 2016. We extracted gibbon calls from the recordings auditorily or visually using spectrograms in RAVEN software. We detected gibbon calls at 40 recording posts during the survey. The proportion of recorders with gibbon calls in the eastern region of Nam Cat Tien sector (mean = 0.79; SE = 0.13) was higher than that in the western region (mean = 0.46; SE = 0.11). The estimated probability of occurrence in the eastern region (ψ = 0.56; SE = 0.20) was higher than that in the western region (ψ = 0.23; SE = 0.16). Passive acoustic data were useful to investigate spatial variation in the probability of occurrence of gibbon. We recommend using autonomous recorders combined with occupancy model to complement human surveyors in gibbon monitoring in areas with low gibbon density because it is efficient, low cost, and not subject to errors caused by human surveyors. In the areas of high gibbon density, absolute density estimate achieved by human surveyors might be a more suitable indicator.

Dispersal and female philopatry in a long-term, stable, polygynous gibbon population: Evidence from 16 years field observation and genetics.

Gibbons are generally reported to live in small socially monogamous family groups in which both sexes disperse when they reach maturity. For the first time, we documented the dispersal pattern in a population of gibbons living in stable polygynous groups (Nomascus concolor) integrating 16 years' field observation and genetic information from fecal DNA. All subadult males except for one dispersed at 9.8 ± 1.4 years of age (range: 8-12, N = 10). The last male remained in his natal group and obtained the breeding position at age 11 by evicting the original dominant male. Females reached sexual maturity (as evidenced by the change in body color from black to yellow) at 8 years (N = 4). Three of them dispersed and one obtained a position as a breeding female and bred in her natal group. We also observed one female returning to her natal group with her infant after her presumed father was taken over by a neighboring male. We identified only three mtDNA haplotypes from 22 individuals at Dazhaizi. Individuals in one group shared the same haplotype, with only one exception. Genetic results showed that the two breeding females were mother-daughter pairs in all three study groups at the end of this study, implying some degree of female philopatry. We argue that in the case of black crested gibbons, dispersal decisions appear to represent highly opportunistic events in response to reproductive opportunities in their natal and neighboring groups.

A distance sampling approach to estimate density and abundance of gibbon groups.

All 18 species of gibbons are considered threatened with extinction and listed on the IUCN Red List of Threatened Species. Because gibbons (Hylobatidae) are one of the most threatened primate families, a great need exists to determine and monitor their status effectively. To meet this need, we employed distance sampling methods to estimate the density and number of gibbon groups. We focused on southern yellow-cheeked crested gibbon in the Nam Cat Tien sector of Cat Tien National Park, Vietnam, from July to October, 2016. We used an auditory point count method at 48 listening posts to detect gibbon groups. We estimated our detection probability of calling groups of gibbons within 1,200 m of a listening post was 0.63 (95% CI: 0.54-0.74). In addition, we estimated the daily calling probability of a gibbon group to be 0.46 (95% CI: 0.33-0.59) and interpreted this as the probability that a group was available to be detected. We adjusted our group density and abundance estimates by both detection and availability probabilities. Ultimately we estimated 325 (95% CI: 232-455) gibbon groups in the Nam Cat Tien sector. Our results suggest that Cat Tien National Park contains one of the largest populations of southern yellow-cheeked crested gibbon in Vietnam. Our methods are one way of avoiding underestimation of gibbon group density and abundance by incorporating uncertainty in gibbon group availability and detection.

Improving the Estimation of Calling Probability and Correction Factors in Gibbon Monitoring Using the Auditory Point Count Method

Estimating the population size of primate species is very important in identifying appropriate conservation actions and measuring their effectiveness. All 17 species of gibbons recognized by the IUCN are considered threatened with extinction. Thus, there is a great need to determine and monitor their status, to conduct effective conservation interventions. Gibbons can be detected by their loud and long song bouts, and surveys usually rely on auditory point count methods. However, gibbon groups do not call daily, so we need a correction factor based on the daily calling probability to estimate gibbon population size accurately. Several studies have estimated such correction factors, but these estimates might be negatively biased if gibbon groups move beyond the maximum hearing distance or are far from the listening post and their calls are faint. We aimed to address this issue and estimate the calling probability and correction factor accurately. We collected data on southern yellow-cheeked crested gibbon (Nomascus gabriellae) in Cat Tien National Park, Vietnam, from July to October 2016, using an auditory point count method. We explored the influence of the maximum distance between the listening post and the gibbons on estimates of the calling probability, correction factor, and population size. We detected 44 gibbon groups during the survey. The calling probability and correction factor decreased with the maximum distance from the listening post to the gibbon groups. If we used all the gibbon groups to estimate the correction factor, population estimates were 15% and 18% higher than those estimated using only gibbon groups detected within 700 m and 500 m, respectively. Based on these findings, we recommend that researchers calculate the calling probability and correction factor for several maximum distances and determine the percentage overestimation of the gibbon population. They should then choose the correction factor so as to balance sample size and the risk of overestimation of gibbon population size.

Gibbons (Nomascus gabriellae) provide key seed dispersal for the Pacific walnut (Dracontomelon dao), in Asia's lowland tropical forest

Understanding the mutualisms between frugivores and plants is essential for developing successful forest management and conservation strategies, especially in tropical rainforests where the majority of plants are dispersed by animals. Gibbons are among the most effective seed dispersers in South East Asia's tropical forests, but are also one of the highly threatened arboreal mammals in the region. Here we studied the seed dispersal of the Pacific walnut (Dracontomelon dao), a canopy tree which produces fruit that are common in the diet of the endangered southern yellow-cheeked crested gibbon (Nomascus gabriellae). We found that gibbons were the most effective disperser for this species; they consumed approximately 45% of the fruit crop, which was four times more than that consumed by macaques – the only other legitimate disperser. Gibbons tracked the temporal (but not spatial) abundance of ripe fruits, indicating this fruit was a preferred species for the gibbon. Both gibbons and macaques dispersed the majority (>90%) of the seeds at least 20 m away from parent crowns, with mean dispersal distances by gibbons measuring 179.3 ± 98.0 m (range: 4–425 m). Seeds defecated by gibbons germinated quicker and at greater rates than seeds spat by macaques, or in undispersed fruits. Gibbon-dispersed seeds were also more likely to be removed by unknown seed predators or unknown secondary dispersers. Overall, gibbons play a key role in the regeneration of the Pacific walnut. Our findings have significant implications both for the management of the Pacific walnut tree dominating tropical rainforest as well as the reintroduction program of the Southern yellow-cheeked crested gibbon.

Ecology and social system of northern gibbons living in cold seasonal forests.

Gibbons in China represent the northernmost margin of present day gibbon species distribution (around N25). Compared to tropical habitats, northern gibbon habitats are characterized by low temperatures and remarkable seasonal variation in fruit abundance. How gibbons adapt to their cold and seasonal habitats and what ecological factors affect their sociality are key questions for understanding their ecology and social system evolution, the elucidation of which will contribute to the conservation of these special populations/species. According to preliminary short-term studies, northern gibbons consume more leaves and use larger home ranges than tropical gibbons. Interestingly, some Nomascus groups consist of more than one adult female. However, these preliminary results are not well understood or incorporated into current socio-ecological theories regarding gibbon species. To better understand northern gibbons, our team has systematically studied three habituated groups of Nomascus concolor, three groups of N. nasutus, and two habituated groups of Hoolock tianxing since 2002. In this paper, we stress the challenges facing gibbons living in northern habitats and summarize their behavioral adaptations to their harsh environments. We also describe the northern gibbon social system and discuss the potential relationships between their ecology and sociality. Finally, we highlight future research questions related to northern gibbons in China.