First record of acoustic behaviour in Sulawesi bear cuscus (Ailurops ursinus)

Possum acoustic behaviour is complex and varies substantially, with some species having numerous calls used in various contexts, while other species are limited to one known vocalisation or non-vocal sounds. Here, we report that the first known recording of Sulawesi bear cuscus (Ailurops ursinus, 1824) acoustic behaviour and observations of associated behavioural displays. We observed an animal adopting a raised posture in apparent threat display and audio-recorded the concurrent short, harsh sounds. The animal produced a ‘chatter’, composed of four notes given at short, regular intervals, followed by a series of ‘clicks’ given at longer and irregular intervals. We describe the frequency and temporal characteristics of these sounds. Clicks were variable in acoustic structure, possibly falling into three subtypes, and some clicks overlapped in acoustic features with individual chatter notes. Click and chatter notes were broadband and non-tonal, and so appear to be non-vocal sounds, produced by the mouth or tongue rather than larynx. Our observations and recording of A. ursinus contribute to the natural history of this poorly known and enigmatic species, that is currently threatened with extinction from illegal wildlife trade, hunting and deforestation.