title: The impacts of logging and hunting pressure on the northern yellow-cheeked crested gibbon (Nomascus annamensis) in Veun Sai-Siem Pang National Park, Cambodia
Creators: name: McGrath, Sarah
Publisher: name: The Australian National University
Year: 2023

description: More than half of the world's primate species are threatened with extinction due to anthropogenic disturbances. Six species of primate are found in Veun Sai-Siem Pang National Park (VSSP) in northeastern Cambodia, including one of the largest known populations of the endangered northern yellow-cheeked crested gibbon (Nomascus annamensis), which was described as a new species in 2010. Illegal selective logging is common in VSSP, and in recent years the use of homemade guns for hunting in the park has increased. However, it is not known how these activities are impacting the primate populations. I conducted semi-structured interviews in five villages surrounding VSSP to investigate the hunting pressure on primates in the park. Additionally, using a multifaceted approach, I investigated the impacts of illegal selective logging on the northern yellow-cheeked crested gibbons. I assessed the impact of chainsaw noise on the activity budgets, ranging behaviour, calling probability, and cortisol levels of the only habituated gibbon group in VSSP. Furthermore, as logging in the park has continued since the time of the previous gibbon survey in 2010, I estimated the density and population size of the gibbons in VSSP and determined the relationship between gibbon density and six environmental variables including distance to logging. Consistent with previous studies, the hunting pressure on the pygmy slow loris (Nycticebus pygmaeus) in VSSP is high. I found that the pygmy slow loris, which is used for traditional medicine, is the most hunted, traded, and sought-after primate in the area. The species most wanted for use as a pet is the northern yellow-cheeked crested gibbon, yet gibbons are not frequently hunted in the park, likely because hunters do not possess appropriate equipment. Compared to previous studies, my findings indicate a shift away from hunting, capturing, and trading long-tailed macaques (Macaca fascicularis) in the region. However, this study was conducted before the COVID-19 pandemic. Given the population greatly declined in the past after being targeted for captive breeding programs and traded internationally for use in biomedical research, it is vital that surveys are conducted to determine if this population was impacted during that period. I found that when chainsaws were active, the gibbons rested more and scanned less, but their calling probability, daily path length and faecal cortisol levels were not affected. These findings show that despite long-term exposure, some gibbon behaviours are altered by chainsaw noise. The gibbon population in VSSP continues to be one of the largest known populations in the world, with an estimated 389 (95% CI 284-542) gibbon groups residing in the park. I estimated that there are higher gibbon calling densities with increasing canopy height, and distance to villages and logging, and in evergreen forest compared to semi-evergreen forest. Four tree species are being targeted for illegal selective logging in VSSP. The variation in the estimated felling times demonstrates that the tree species selected for logging changes over time. These findings suggest that illegal selective logging will continue in VSSP unless major changes to law enforcement activities are made.