Effects of chainsaw noise on the activity budgets and calling behaviour of the northern yellow-cheeked crested gibbon (Nomascus annamensis)

Abstract

Wild animals are increasingly subjected to noisier environments as the scale and scope of human activities, such as development and resource extraction, encroach into their habitats. Anthropogenic noise alters the behaviour and vocalisations of wild animals including primates, yet our understanding of how noise affects small apes is limited. The large population of endangered northern yellow-cheeked crested gibbons (Nomascus annamensis) inhabiting Veun Sai-Siem Pang National Park (VSSP), in northeastern Cambodia, is frequently exposed to noise produced from illegal selective logging activities within the park. To determine the impacts of chainsaw noise on the gibbons' activity budgets and calling probability, we collected behavioural data on the only habituated gibbon group in VSSP during two consecutive dry seasons between 2017 and 2019. Our analyses of scan and focal-animal samples revealed that when chainsaws were active, the group rested more and scanned less. The gibbons called more on mornings when there was no chainsaw activity; however, the trend was non-significant. These findings suggest that despite long-term exposure, chainsaw noise variably impacts important aspects of gibbon behaviour.