Multicopter-Assisted Acoustic Surveys Complement Ground-Based Transects in Assessing Bat Activity and Species Group Composition

Abstract

The use of multicopters in ecological fieldwork is expanding rapidly, offering new opportunities to monitor species in otherwise inaccessible environments. Bats, in particular, pose a methodological challenge due to their nocturnal and aerial behavior, and many species are difficult to detect using ground-based surveys alone. In this study, we evaluated the potential of multicopter-based acoustic transects as a complementary method to traditional ground-based bat surveys. We compared species group composition and activity levels acoustically recorded along identical transects at ground level and at 104 m height with a multicopter across three habitat types (forest, meadow, and waterbody). Our results showed that elevated airspace appears to represent a largely distinct foraging habitat that is only partly linked to ground-level habitat structure and is primarily used by Nyctaloid and Pipistrelloid echolocation groups. Our findings are in line with what is already known about the spatial behaviour of Myotis bats, as these were recorded almost entirely near the ground. We also tested whether the two multicopter types influenced acoustic detection rates and found no significant differences when recording devices were properly distanced and oriented away from the multicopter. Thus, this paper contributes by suggesting how multicopters can serve as a new mobile measurement method to extend the vertical reach of acoustic bat surveys. This further helps to identify species-specific habitat use in hard-to-reach regions, such as the risk area around the nacelle of a wind turbine. This information can then be used to inform bat conservation and mitigation efforts.