Conservation strategies for Delacour’s langur (Trachypithecus delacouri) in Vietnam: Behavioural comparisons and reviewing a release

Abstract

Delacour’s langur (Trachypithecus delacouri) is a critically endangered Southeast Asian colobine, found in the karst outcrops of northern Vietnam. Half of the remaining population (estimated at fewer than 200 individuals) resides within Van Long Nature Reserve, Ninh Binh Province. This thesis aims to further the conservation of T. delacouri by reviewing the first release of captive-bred individuals as a potential conservation tool for the species, along with acquiring a greater understanding of the species’ behaviour. Behavioural focal observations were conducted throughout 2011, both on wild groups at Van Long and captive individuals at the Endangered Primate Rescue Center (EPRC) at Cuc Phuong National Park. A group of three individuals was released by the EPRC into Van Long in August 2011 in an aim to connect populations and promote interbreeding, and was tracked using GPS radio collars for a period of up to 13.5 months, with the release then evaluated in line with IUCN reintroduction guidelines. Activity budgets of the wild versus captive T. delacouri populations showed significant differences, although both were in line with typical colobine budgets. Inactivity dominated (wild 75.0%, captive 61.9%), with feeding behaviours also playing a major part (wild 21.3%, captive 29.0%). Sex differences were minimal, but age differences showed that young were more social, and adults spent more time inactive and less time feeding. Both affiliative and antagonistic social interactions were common, with females and young most likely to be involved in affiliative behaviours. Infants showed significant changes in their behaviour as they aged, becoming increasingly social and independent, with allomothering witnessed. Vocalisations were predominantly performed by adult males, with grunts the most common call (61.2%) of the seven identified. An individual’s sex/age class was significantly linked to the type of vocalisation performed. T. delacouri vocalisation behaviour was relatively similar to that of other limestone langurs, although some differences in call structure were found. The released individuals all survived for a minimum of five months before tracking was disrupted for one, showing some wild-like behaviours, although their behaviours were largely atypical. The group quickly separated to travel as individuals, and ranged extensively with the adult male covering 1020ha in 9.5 months. Average day journey lengths were comparable to other limestone langurs (453m–735m), but the individuals did not develop distinct home ranges. A strong diurnal trend in movement showed two peaks at early morning and late afternoon, but minimal seasonal differences were detected. More extensive monitoring is needed to determine whether or not the release was a success, but the project fulfilled an important role as a pilot study to learn how best to conduct a release and how the animals will behave. In reviewing the release it was found to have broadly followed the IUCN guidelines, although gaps were identified suggesting more formalised planning, risk assessments, and consultation was needed. Moving forward, the possibility of translocating existing T. delacouri subpopulations, rather than conducting further captive releases, should be explored as a conservation strategy, along with continuing the effective protection measures in place at Van Long.