Drone-based wildlife surveys elicit minimal vigilance in nocturnal arboreal mammals: evidence from comparisons with ground-based detection methods

Wildlife surveys are essential for monitoring populations, informing conservation actions, and assessing impacts of environmental change and management activities. Emerging technologies such as drones are increasingly used for habitat mapping and wildlife detection and monitoring, offering advantages, including greater survey coverage and improved detection rates, and are therefore attractive for wildlife research and conservation efforts. However, their increased application raises important animal welfare concerns, as drones may introduce novel stimuli such as noise, rotor downwash or artificial illumination that may provoke behavioural disturbance. Using over 900 thermal-infrared video recordings collected during drone surveys for nocturnal arboreal mammals in temperate Eucalyptus forests of south-eastern Australia, we assessed whether animals noticed the drone and exhibited behavioural changes, including those indicative of vigilance. These observations were compared with behaviour recorded during traditional ground-based spotlighting surveys. Across all species observed, behavioural responses to drone observation were minimal – only 17% of individuals appeared to notice the drone and 11% exhibited vigilant behaviour, with no evidence of flight responses. By contrast, spotlighting elicited vigilance in most animals, with individuals being over 19 times more likely to remain calm under drone observation than under spotlighting. Species-specific analyses showed that generalist species such as common ringtail possums (Pseudocheirus peregrinus) and brushtail possums (Trichosurus spp.) displayed very low vigilance during drone flights, whereas gliding and acoustically communicative species such as southern greater gliders (Petauroides volans) and yellow-bellied gliders (Petaurus australis) were more sensitive but still considerably less reactive than during spotlighting. Seasonal variation also influenced responses, with vigilance highest in autumn – often associated with breeding activity in arboreal marsupials – and lowest in spring. Our findings indicate that drone-based survey methods provide an effective and minimally invasive approach for monitoring arboreal mammals while maintaining ethical survey standards and reliable behavioural data.