Abstract: Passive acoustic monitoring technology has recently been widely used in the monitoring of terrestrial mammals. Such technology enables the unattended monitoring of wildlife in specific areas at low cost and in a non-invasive manner. The main problem, however, is the need to retrieve data manually. Moreover, the subsequent data analysis and sorting are more complicated. In this study, a passive acoustic monitoring system was designed for monitoring the western black crested gibbon (Nomascus concolor). The monitoring system is powered by solar energy in the field. Sound data are collected by the directional pick-up array. The data are transmitted through a wireless network to a server in the management office building. Researchers are assisted in identifying the sound and the direction of the sound by the sound-data management system, which simplifies the data collection and processing. The system has continuously monitored two groups of western black crested gibbons for 351 days at the scientific monitoring site of Pipaqing in the Ailao Mountain Nature Reserve. Results showed that the system had a long continuous run-time and was not affected by the weather conditions; data transmission was convenient and efficient; the directions of sound source could be well determined by the directional pick-up array, overcoming the shortcomings of traditional monitoring equipment; the system had advantages over manual monitoring methods in terms of data continuity and integrity, intelligence in data processing, and monitoring costs. This system meets the continuous long-term monitoring needs of western black crested gibbons, and may be improved and applied in the future as an automated solution for the monitoring of this primate species.

Key words: Passive acoustic monitoring, Directional pickup array, Western black crested gibbon, Sound source localization