Acoustic monitoring with miniature drones shows reduced Myotis bat occurrence with altitude and drone movement

Abstract

Abstract Our understanding of aeroecology is hampered by the challenge of sampling the air column, especially for nocturnal species like bats that forage high in the airspace. Nonetheless, monitoring endangered bat populations is vital for conservation efforts. Drones (unoccupied aerial vehicles) offer a relatively safe, cost-effective, and non-intrusive option for studying aerial wildlife. Here, we present a method for measuring bat distribution in the airspace using miniature drones (Mavic Mini 3 Pro) that are small enough to have negligible impacts on the bats themselves. We investigate how habitat, drone altitude, and drone movement influence bat sampling efficiency. A hovering drone detected more bats per minute than a moving drone for the EPNO complex (Eptesicus fuscus and Lasionycteris noctivagans) and all bats. Thus, we recommend the use of hovering point counts for surveying bats via drone. The Myotis complex (M. septentrionalis, M. lucifugus, and M. leibii) was more frequently present at lower altitudes over the sampled range (0–60 m). We conclude that bat taxa differentially occupy sectors of the air column, and that bat density in the airspace can be efficiently monitored by miniature drones.