Habitat Occupancy and Activity Patterns of Pig-Tailed and Long-Tailed Macaques in Forest Fragments and Oil Palm Plantation in Northern Sarawak, Borneo

Oil palm plantations have significant and complex effects on biodiversity particularly in tropical rainforest regions such as Borneo, where vast tracts of forest have been converted into monoculture plantations. Such human-altered environment is utilised by generalist species such as the sympatric pig-tailed macaque (Macaca nemestrina) and long-tailed macaque (Macaca fascicularis), which exploit the structural and trophic resources available in these modified landscapes. Therefore, this research aims to investigate the habitat utilisation of macaques within forest fragments surrounded by oil palm plantation. Camera traps were deployed in WPSB oil palm plantation in northern Sarawak in two phases: Phase 1 with 6-months sampling period (2013–2014) and Phase 2 with 14-months sampling period (2018–2020), targeting the High Conservation Value area, remnant forest patches and in the plantation itself. The study was performed by comparing the occupancy and activity patterns of both macaque species through camera trapping deployed in the oil palm plantation, forest fragments and at the forest edges. Package “jagsUI” was used to analyse single-species occupancy model (SSOM) and Royle-Nichols abundance estimate model (RNAEM) while package “overlap” was utilised for the activity pattern analysis. SSOM showed that longer sampling period distinctly results in both species having high probability of occupancy and probability of detection in forest fragments and forest edges compared to the plantations. Occupancy modelled along distance gradient exhibited that pig-tailed macaque is more forest dependent while long-tailed macaque has higher probability in the forest edge. Both species showed high levels of overlapping in activity, with distinct peak activity for each species in each habitat. While the findings of this study should be interpreted with caution due to the arboreal nature of these species, the results provide insights into the co-occurrence of pigtailed macaques and long-tailed macaques in oil palm plantation landscapes, suggesting that both species exhibit overlapping temporal and spatial patterns. Understanding the dependency of macaques on oil palm plantation landscapes may aid in the conservation management of these species, particularly in Borneo, as both are currently listed as Endangered in the recent IUCN Red List assessment.