A mixture of artificial and biological sounds improves the effective range of an acoustic repellent for an invasive lizard species

Further range expansion of invasive animal species can be prevented by controlling their behavior. Acoustic repellent is a promising approach to deter problematic animals from ecologically sensitive areas. To develop an acoustic repellent system for a green anole that was introduced to the Ogasawara islands in Japan, this study evaluated the deterrent effect of (1) a pattern sound of machine noise and (2) a mixture of artificial and biologically relevant sounds. We created a sound level gradient inside a small experimental cage in a laboratory setting and measured whether green anoles avoided the vicinity of a speaker. In approximately 80% of cases, both the pattern machine sound and the mixture sounds prevented green anoles from stepping into the vicinity of a speaker (<24 cm). The mixture sounds maintained the deterrent effect at a middle distance from a speaker (<72 cm), whereas the pattern machine sound did not work as a strong acoustic repellent at this distance. These results imply that the mixing of biotic and abiotic sounds can improve the effective range of acoustic repellent for green anoles. However, several shortcomings of the acoustic repellent system were also highlighted. Since a green anole is an insectivore predator, our findings will contribute to protecting endangered native insect fauna from the predation of non-native lizard species.