Northern white-cheeked gibbons in Lao 773
decade is a brief period in the life history of gibbons. They reach sexual maturity, and thus dispersal age, at the age of 10 years (Reichard & Barelli, 2008) with males dispersing mostly into neighbouring groups (Matsudaira et al., 2018). Thus, as gibbon home ranges are relatively small (c. 25 ha; Bartlett et al., 2015) it is unlikely that suitable habitat is rapidly colonized. This probably makes gibbon populations slow to recolonize the entire Protected Area, which may take at least 20–30 years if there is no further disturbance (Caldecott & Miles, 2005). This slow population recovery could be the reason why we did not find a significant link between hunting pressure and distance to the core zone boundary, although hunting is widespread over the entire Protected Area (Fig. 3b). Although apparently suboptimal, the large continuous
areas of deciduous forest could be adequate for gibbon per- sistence, as indicated by Phiphatsuwannachai et al. (2017) for lar gibbons. These authors observed that deciduous trees in this forest type often carry flowers or fruit sufficient to support low density gibbon populations. Future studies should examine whether northern white-cheeked gibbons maintain larger home ranges in less productive habitats as observed elsewhere for lar gibbons (Savini et al., 2008; Phiphatsuwannachai et al., 2017). A study of Nomascus ga- briellae in Seima Biodiversity Conservation Area, Cambodia, found no significant differences in group densities across evergreen, semi-evergreen and deciduous forest, supporting the view that gibbons are more flexible than previously thought with regard to habitat usage (Rawson et al., 2009). Such flexibility could support gibbon resilience in the face of moderate habitat degradation and thus, under appropriate circumstances, open the possibility of conserving other habitat types for gibbons. Despite not covering the entire Protected Area, our
findings confirm that Nam Et-Phou Louey National Protected Area holds a significant, albeit small, population of northern white-cheeked gibbons. The results are fun- damental for understanding the regional status of this Critically Endangered species and for protecting its habi-
tat.Although the population in the study area iswidely dis- persed, it tends to be more abundant in deciduous forest. This indicates that both evergreen and deciduous forests should be considered as priority habitat for protecting this species. We recommend that the gibbon population at the Protected Area should be surveyed every 5 years to investigate evidence for the species’ recovery and monitor the effectiveness of the current protection
plan.Moreover, sociodemographic changes in selected family groups should be monitored annually to estimate population viability in both evergreen and deciduous forests. A study determining whether the density of gibbon territories in- creases in evergreen forest habitat as a result of inward mi- gration would be of value. Law enforcement patrols should continue in the key areas containing gibbons, to reduce
threats. This should preserve the existing population, with particular attention to the northern part of the study area, where more groups live (Fig. 3a). A forest management plan is required to maximize quality habitat and ensure habi- tat connectivity. Finally, public awareness is also needed to ensure relevant stakeholders are involved in gibbon protec- tion, and to contribute towards a more sustainable manage- ment of the Protected Area.
Acknowledgements We thank Nam Et-Phou Louey National Protected Area for providing permission to conduct this research, GIS data and survey field assistants; Paul Eshoo for his advice; all field survey teams comprising Nam Et-Phou Louey National Protected Area officers, rangers, and local villagers for their assistance; Camille Coudrat and Chanthalaphone (Project Anoulak) for field training; Greg Irving for language editing, and two anonymous re- viewers for their critiques. We acknowledge funding from the Ocean Park Conservation Foundation Hong Kong and the Wildlife Conservation Society Lao Programme.
Author contributions Study design: KS and TS; data collection: KS; data analysis: KS, DN, and TS; writing: all authors.
Conflict of interest None.
Ethical standards This research abided by the Oryx guidelines on ethical standards and was carried out in accordance with the laws of Lao PDR.
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