Conservation Ecology of Bornean Orangutans in the Greater Batang Ai-Lanjak-Entimau Landscape, Sarawak, Malaysia

Abstract

The Bornean Orangutan (Pongo pygmaeus) is one of the three great ape species in Asia. P. pygmaeus is further divided into three subspecies based on their genetic divergence. These subspecies are also geographically apart from each other; with the Malaysian state of Sarawak having the least number of wild orangutans. In 2016, the threat level for the species was upgraded to ‘Critically Endangered’ under the IUCN Red List of Threatened Species. The alarming upgrade was due to increased threats to the survival of the species in Borneo, mainly due to habitat degradation and forest loss as well as hunting. The actual orangutan numbers in the wild were still unclear despite the upgrade due to wide variance generated from various statistical methods or survey protocols used to estimate them. In Sarawak, the conservation efforts have been ongoing with the focus on preventing further population decline, habitat degradation and forest loss. The first step in this effort was to acquire baseline data on population estimates and distribution at the core habitats of Batang Ai-Lanjak-Entimau (BALE) where most of the viable orangutan populations are found in the State. The data were needed for drafting a policy on a long-term strategic action plan for orangutans at the greater BALE Landscape. If the policy is approved, collaboration is anticipated between conservation partners and government agencies to implement the recommendations. These cover a wide range of disciplines including science, technology, policy and socio-economy. The purpose of this thesis is then to provide a comprehensive and updated report on orangutan conservation in Sarawak for the intended joint collaborators. This thesis expounds on the current threats and conservation strategies in Sarawak, recent population and distribution studies at the Batang Ai-Lanjak-Entimau (BALE) Landscape, and recommendations for future studies at other focal sites with remnant orangutan population outside the core habitats of BALE. One of the major findings include a combined estimate of 355 orangutans with the 95% highest density interval (HDI) of 135 to 602 individuals at the project sites. The outcomes of this project show that the survey designs using Bayesian analyses were a novel approach for site-specific studies, and the results complemented the growing scientific repository on orangutan population studies in Borneo. I conducted this project in collaboration with the Wildlife Conservation Society (WCS) Malaysia, the organization that sourced the unpublished data used for the analysis of this project. WCS has conducted orangutan nest count surveys at the BALE Landscape since 1991. For the population study, I used new orangutan nest data recorded during the surveys conducted between 2011 and 2015. Subsequently, I combined this data with surveys conducted between 2003 and 2007 as an academic exercise to map proxy orangutan distribution. The survey designs for both the population and distribution studies as shown in the Supplementary Materials were developed by Mike Meredith, the main statistician of this project. I ran the data analysis and compiled the R graphic outputs for the thesis chapters. This thesis should be of interest to policy makers in the Forest Department, Sarawak Forestry Corporation, private organizations and research institutions, as well as local and international collaborators for the implementation of the policy on zero-loss of orangutans and their habitats. It should also be of interest to scholars of great ape ecology and conservation, as well as of land use planning and protected area management.