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At the present time, the Van Long Nature Reserve Ninh Binh Province is home to the only viable sub-population of the ‘Critically Endangered’ Delacour’s langur (Trachypithecus delacouri). The reserve contains about 200 individuals. The next largest sub-population of about 80 individuals exists in neighboring Ha Nam Province, in a currently unprotected area. Such small and isolated populations have heightened vulnerability to internal and external threats to their survival. The establishment of further sub-populations in suitable, secure and sustainable locations, therefore, is a crucial step towards helping to safeguard the survival of this species. Until the late 1990’s a small population is known to have existed in the Trang An limestone massif, Ninh Binh Province. In 2014 Trang An was inscribed as UNESCO World Heritage Site. With strict protection of the area now in place and the existing and excellent habitat that the massif offers for Delacour’s langurs, the establishment of a new sub-population here was recommended soon after its inscription and is included in the “Urgent Action Plan for the Conservation of Primates in Vietnam until 2020, Vision 2030”. The Endangered Primate Rescue Center (EPRC), located in Cuc Phuong National Park, started breeding programs for several species of highly endangered primates in 1993, with the goal of releasing captive born individuals to support depleted wild populations or to establish new populations where the species has been extirpated. In 2017 a collaborative venture between local, national and international stakeholders was initiated to set in motion a reintroduction program for Delacour’s langurs in Trang An. In August 2020, a group of three captive-born Delacour’s langurs was transferred to an island in the World Heritage Site as a first step towards a possible re-establishment of a sub-population in this area.

This study draws on the local ecological knowledge of 58 hunters from seven communes in the Ngoc Son Ngo Luong Nature Reserve (Hoa Binh province, North Vietnam) to examine the local status of 40 threatened vertebrates. The reserve forms part of a biodiversity-rich mountainous corridor. Respondents were shown photographs of the species and asked to rate their abundance on a scale of 0–3 (0, extinct; 3, very abundant) in two periods: pre-1975 (before Doi Moi) and in 2009. The results show that 39 species have lived in the area and five are now extinct (Delacour's langur Trachypithecus delacouri, northern white-cheeked crested gibbon Nomascus leucogenys, dhole Cuon alpinus, oriental small-clawed otter Aonyx cinereus, Indochinese tiger Panthera tigris corbetti) and the presence of another six is doubtful (Phayre's leaf-monkey Trachypithecus phayrei ssp. crepuscula, sun bear Helarctos malayanus, binturong Arctictis binturong, fishing cat Prionailurus viverrinus, leopard Panthera pardus, wreathed hornbill Anorrhinus undulatus). The results show a general decline in numbers and abundance, with mammals declining fastest, especially carnivores and primates. The differences in abundance between species have narrowed since 1975, converging towards trends of general impoverishment at similar low abundances. The survey results were similar among communes and also concord with the findings of research in nearby areas. This study demonstrates the usefulness of local ecological knowledge for planning, decision-making and management of protected areas in the absence of historical records or financial resources for conducting intensive fieldwork in remote and little-known areas.

Information on positional behavior can help elucidate relationships between a species’ morphology, behavior, and environment. Delacour’s langurs (Trachypithecus delacouri) are similar to other colobines in body mass and intermembral index, yet inhabit a limestone karst environment. From August 2007 to July 2008, we collected 372 h of positional behavior and substrate use data from 8 groups of Trachypithecus delacouri in Van Long Nature Reserve, Vietnam to address questions about how the distinct —and potentially dangerous— features of karst influence colobine positional behavior. Results show that Trachypithecus delacouri is predominantly quadrupedal (66%). However, they exhibit differences that set them apart from many other colobines. Nearly 80% of locomotor and postural behaviors were performed on rocks. Leaping was remarkably infrequent, representing only 6% of overall locomotion. They leapt 3 times more frequently on trees (13%) than on rocks (4%) and more frequently used trees as a landing substrate than rocks (38% vs. 23%), both significant differences. We argue that rock (and cliff) travel is altogether different from terrestrial and arboreal travel and propose using the term petrous to indicate the substrate and incorporate the implications of its precise sharpness and verticality that lead to the complexities and risk of locomotion on rock surfaces. Trachypithecus delacouri does not show specific adaptations for limestone karst. Instead they appear to be a behaviorally flexible species and, owing to the generalized locomotor capabilities that characterize cercopithecids, capable of locomoting through and living in the limestone rock environment to which they have relatively recently been restricted.

Trachypithecus delacouri (Osgood, 1932), commonly called Delacour's langur or lutung, is a black and white lutung (leaf monkey) endemic to northern Vietnam. It is a diurnal and primarily arboreal species, but spends more time on the ground than other species of Trachypithecus. T. delacouri lives among limestone cliffs and consumes the leaves of a broad spectrum of plant species but its choice of food items tends to be based on the chemical makeup of the plant phenophases with protein content the strongest predictor of leaf selection. Territorial, but with overlapping territories, it usually lives in single-male–multifemale groups of 5–30, although 2 adult males may be present. With a declining population perhaps as low as 200 individuals in 17 or fewer isolated populations, it is 1 of the world's most endangered primates.

Trachypithecus cristatus (Raffles, 1821), silvered lutung, is a colobine monkey of the Malay Peninsula and Archipelago. It has a pointed crest and outward-projecting cheek hairs, and gray skin and pelage with some grayish white hairs that are lighter distally, giving a silvered appearance. Diurnal and arboreal, it runs and jumps quadrupedally, with limited semibrachiation. Its large stomach and foregut fermentation allow it to digest a diet with a high proportion of leaves. It lives in single male-multifemale groups and smaller multimale groups in a polygynous, cooperative-breeding mating system. As with other nonhuman primates, it is threatened throughout its range by logging, hunting for meat and medicinal uses, and capture for the pet trade. DOI: 10.1644/862.1.

Colobines are similar in their exploitation of a high percentage of leaf matter. However, this observation obfuscates interesting differences among genera of Southeast Asian colobines in morphology and behavior that may be reflected in the degree to which they rely on mastication or gut volume and gut retention time when ingesting and digesting leaves. We detail the use of a laboratory-based method to measure the mechanical properties of foods selected and processed by 4 captive species of Southeast Asian Colobinae —Pygathrix nemaeus, Pygathrix cinerea, Trachypithecus delacouri, and Trachypithecus laotum hatinhensis— at the Endangered Primate Rescue Center (EPRC), Vietnam. We also detail a field method that quantifies chewing rates and chewing behavior via a consumer-grade video camera and laptop computer. Observations in the captive setting permit a degree of experimental control that is not possible in the wild, and the location of the EPRC in the primates’ habitat country permitted us to provide leaves that they encounter and eat in the wild. We collected toughness data with a portable tester designed by Lucas et al. The average toughness of selected leaves does not differ among the taxa, nor does the length of time spent chewing foods. However, there are differences in feeding rate, with Trachypithecus spp. chewing foods twice as fast as Pygathrix spp. Our findings suggest that Trachypithecus spp. emphasize comminution of food by mastication, while Pygathrix spp. emphasize the comminution of leaf matter in the stomach. The hypothesis is supported by data on molar size, gut mass, and gut morphology. We provide new insights into dietary variation among primate species and detail methods that are typically conducted only in a laboratory setting. We augment the findings with additional data on activity, feeding rates, and tooth morphology.

More than 70 h of positional behaviour data were collected on the red-shanked douc langur Pygathrix nemaeus, Delacour's langur Trachypithecus delacouri, Hatinh langur Trachypithecus laotum, and the white-cheeked crested gibbon Hylobates leucogenys in January and February of 2001 at the Endangered Primate Rescue Center of Cuc Phuong National Park, Ninh Binh Province, Vietnam. Equal amounts of instantaneous and continuous bout data were collected for each of the four species. All animals were housed in enclosures of 10×5×3.5 m with similar substrates, and lived in small, species-appropriate social groups. The positional behaviour of white-cheeked crested gibbons was as expected with >80% of locomotor bouts and 60% of postures being suspensory in nature. The positional behaviour of the Delacour's and Hatinh langurs was similar to that reported in the literature for other Asian colobines with >90% of the locomotor bouts being quadrupedal walking, running, and bounding on tops of arboreal supports. Postures were dominated by sitting in and sitting out with forelimb suspension associated with

The six limestone langur taxa of Southeast Asia inhabit the rugged limestone karst mountains, although the reason for their current restriction to this habitat is unclear. From August 2007 to July 2008, I collected data on the diet and feeding behavior of the critically endangered Delacour's langur (Trachypithecus delacouri) in Van Long Nature Reserve, Vietnam. I used these data to evaluate the hypothesis that limestone langurs are found on karst habitat because they depend on endemic limestone plants. Feeding accounted for 29% of the langurs' activity budget. Young leaves dominated the diet monthly, seasonally, and annually. The annual diet consists of nearly 79% foliage with almost 60% young leaves. Despite a distinct wet and dry season, over the study period, seasonal variation in plant part consumption was slight. Fruit and seeds were a small contribution to the diet. Delacour's langurs ate 42 of 145 available species, and they concentrated on a subset of this number. Five plant species comprised more than 60% of the diet and 16 species comprised more than 93%. More than half of the diet came from climbers. Delacour's langurs are among the most highly folivorous of studied colobines and, along with the closely related T. leucocephalus of southern China, the most folivorous of the Asian langurs. Whether high folivory is owing to a lack of available fruits and seeds in limestone habitats is unknown. What is certain, however, is that the plant species most important in the Delacour's langurs' diet at VLNR, throughout the study, were not plants endemic to limestone. Feeding dependence alone, therefore, cannot explain the current distribution of limestone langurs on karst habitat. Am. J. Primatol. 72:317–324, 2010. © 2009 Wiley-Liss, Inc.

Recent studies at the Endangered Primate Rescue Center (EPRC) in the Socialist Republic of Vietnam's Cuc Phuong National Park by Byron et al. ([2002] Am. J. Phys. Anthropol. [Suppl.] 34:51) and Covert and Byron ([2002] Caring for Primates) revealed unexpected locomotor and postural behaviors in the red-shanked douc langur (Pygathrix nemaeus). This paper further elucidates the question of red-shanked douc suspensory behavior, and provides initial positional behavior data for two other rare Asian colobines, by comparing the ontogenetic positional behavior of red-shanked douc langurs, Delacour's langurs (Trachypithecus delacouri), and Hatinh langurs (Trachypithecus hatinhensis) at the EPRC. Two hundred and seven hours of positional behavior data were collected, with approximately equal amounts of data on each species, and equal amounts on adults and those less than 18 months in age. All young animals were more active than adults, used a wider repertoire of locomotor behaviors, and expressed suspensory behaviors more frequently than did the adults. Young animals also "invented" one new locomotor and two new postural behaviors. These differences are due to both play and explorative behavior, as well as to the youths' changing musculoskeletal systems. The number of positional behaviors utilized by the adults of these species is quite similar to one another (23-32), as is that utilized by the young (51-56). Douc langurs in both age categories used suspensory behaviors more frequently than did Delacour's and Hatinh langurs. Because the uniformity of enclosures offers a control, the results of this study generate hypotheses regarding adaptive radiations and niche partitioning in wild populations.