Sound Playback Surveys to Reveal the Distribution of Invasive Alien Pallas's Squirrels, Callosciurus erythraeus

The Pallas's squirrel (Callosciurus erythraeus) is one of the invasive alien species in Japan. Although control measures for this species have been attempted for a long time, the eradication has not succeeded and the populations continue to increase. To initiate control of the invasive alien squirrels as soon as possible, we have to detect their existence at low density stage soon after colonization. The Pallas's squirrels are known to use acoustic signals when encountering predators and during mating chases. We tested the effectiveness of playback surveys in monitoring the Pallas's squirrel. The squirrels were attracted by mobbing sounds in 63 to 83% of trials, and by mating sounds in 24 to 27% of trials conducted in Kamakura City where Pallas's squirrels had established 60 years ago. In 34 isolated woodlots of Iruma City where Pallas's squirrels has been introduced recently, we found the squirrels in two woodlots by direct observation, but detected in other three woodlots by playback surveys. The sound playback method appears useful to detect Pallas's squirrels even in low density situations.