Ecology, behavior and conservation of the Tonkin snub-nosed monkey (Rhinophithecus avunculus) in Vietnam

Abstract

The Tonkin snub-nosed monkey (Rhinopithecus avunculus) is a critically endangered primate and endemic to northern Vietnam. This research was to address the questions about ecology and behavior of a relatively unstudied species in comparison with the other members of the genus Rhinopithecus. I carried out my study in Tat Ke Sector, Na Hang NR and Khau Ca HSCA over 24 months, from September 2004 to September 2006. In addition, four other known sites including Ba Be NP, Nam Xuan Lac HSCA, Than Sa-Phuong Hoang and Cham Chu NRs were also investigated between 2006 and 2010.

Tat Ke and Khau Ca have a relatively similar botanical structure and species composition. The main forest type here is evergreen forests associated with limestone hills. Phenological patterns at both sites were characterized by high production of young leaves throughout the year and seasonality of flowers and fruits. Rainfall correlated with the production of young leaves, flowers and fruits.

The social organization follows the typical patterns of other colobines in that the basic structure is one-male unit (OMU). Extra males form all-male units (AMUs). OMUs and AMUs frequently aggregated in large bands for traveling, feeding, resting and sleeping. The species show fission and fusion society as probably as a result of the size of food patches, the abundance and availability of quality food, and human disturbance. Members within OMU have high cohesiveness as a result of close social distance. Social and agonistic interactions within and between units are infrequent, as with many colobines. Males respond aggressively toward the resident males of other one-male units, suggesting the defense of females. Grooming is mostly performed by adult females, suggesting high affiliation between them within OMUs. Juveniles observed provided alloparenting. Seasonality of birth may be related to food quality and the availability of food items. The colour ofthe newborn observed is in contrast to previous reports on R. avunculus and differ from the common pattern in most colobine species. Other new observations on behavior described in this study include group movement, vocalizations, rest-huddling, and terrestriality. In contrast to previous reports, R. avunculus in this study is folivore and frugivore, with an emphasis on young leaves (46.2%). The species were highly selective in their choice of foods and fed mainly from trees which were quite rare and low in terms of both the number of stems and basal area. Strong selectivity for uncommon species has been reported in several colobines and may be related to nutritional quality, abundance and availability of food items. Diet of the species at Khau Ca varied according to seasonal changes in availability of food items, as with many other primates.

The total population estimated for Vietnam is ca. 215 individuals. Population sizes are decreasing in most of the sites surveyed, the only exception being Khau Ca. This results from high hunting pressure and habitat destruction. Immediate conservation measures need to be taken to protect small remaining populations of the species and its habitat before they become locally extinct as in Ba Be NP.