A Feasibility Study on the Use of Vocalizations of Wild Macaque Troops to Determine Location

We investigated the possibility of detecting wild Japanese macaque troop locations based on their vocalizations on Yakushima Island, a typical habitat of this species, in order to design adequate census methods and observe wild monkeys more efficiently. For each category of vocalizations we determined the maximum distance between the observers and the vocalizing monkeys. Trackers and fixed-point observers determined the actual real-time location of the vocalizing monkeys. ”Loud calls” and ”loud screams” could travel the farthest distance and were most suitable for obtaining precise directional estimation on the position of the troop. The maximum distance from which ”loud calls” were heard was 580m, and that for the ”loud screams” was 420m. However, it was concluded that when conducting censuses by using vocal cues in steep terrain like on Yakushima Island, the frequencies of these two vocalizations might sometimes be too low to conduct a census efficiently. Thus, we recommend that a more effective detection distance should be less than 200m, which is close enough to hear the next long-distance transmittable vocalizations such as ”loud aggressive vocalization” and ”loud alarm calls.” Although loud alarm calls were less precise when determining the direction from which the voice came, they were more practical for large-scale census methods.