Batmobile—using nocturnal drone imagery to assess the habitat use and population size of a tropical island-endemic flying-fox

Members of the Pteropus genus (flying-foxes; fruit bats) occur predominantly on tropical islands, where they fulfil critical ecological roles as pollinators and seed dispersers; however, most of these species are under threat and sound population monitoring is an urgent requirement. Pteropus natalis (Christmas Island flying-fox) is classified as critically endangered and is the sole remaining endemic mammal on Christmas Island. The conservation management of this species has been hindered by difficulties in reliably monitoring its population due to challenging terrain and the species' behaviour. In this study, we used nocturnal drone-acquired thermal video imagery to detect P. natalis while foraging. Using a stratified random sampling method, we surveyed 43 5-ha plots across six vegetation types on Christmas Island. Pteropus natalis were detected most frequently in perennial wetlands, aligning with known habitat preferences. Extrapolating detections across the total area of each habitat type yielded a population estimate of 4441 (±64.0 SE), aligning with recent estimates obtained from a range of more labour-intensive methods. Our findings highlight the potential utility of nocturnal thermal drone surveys for monitoring population sizes and habitat use of island endemic flying-foxes, offering a scalable and efficient alternative to traditional survey methods for this ecologically important group.