A Novel Scouring Method to Monitor Nocturnal Mammals Using Uncrewed Aerial Vehicles and Thermal Cameras—A Comparison to Line Transect Spotlight Counts

Abstract

Wildlife abundance surveys are important tools for making decisions regarding nature conservation and management. Cryptic and nocturnal mammals can be difficult to monitor, and methods to obtain more accurate data on density and population trends of these species are needed. We propose a novel monitoring method using an aerial drone with a laser rangefinder and high zoom capabilities for thermal imagery. By manually operating the drone, the survey area can be initially scanned in a radius of several kilometers, and when a point of interest is observed, animals could be identified from up to one kilometer away by zooming in while the drone maintains an altitude of 120 m. With the laser rangefinder, a precise coordinate of the detected animal could be recorded instantly. Over ten surveys, the scouring drone method recorded significantly more hares than traditional transect spotlight count surveys, conducted by trained volunteers scanning the same farmland area within the same timeframe (p = 0.002, Wilcoxon paired rank test). The difference between the drone method and the transect spotlight method was hare density-dependent (R = 0.45, p = 0.19, Pearson’s product–moment correlation); the larger the density of hares, the larger the difference between the two methods to the benefit of the drone method. There was a linear relation between the records of deer by the drone and by spotlight (R = 0.69, p = 0.027), while no relation was found between the records of carnivores by drone and spotlight counts. This may be due to carnivores’ speed and vigilance or lack of data. Furthermore, the drone method could cover up to three times the area within the same timeframe as the transect spotlight counts.

Thermal scanners versus spotlighting: New opportunities for monitoring threatened small endotherms

“…While spotlights also rely on direct line of sight, almost all endotherms detected with spotlights were flying or running from their roost site upon detection, and would most likely be detected regardless of vegetation openness when they move into an open area. It is also possible that endotherm abundance was different between years and sites due to vegetation structure, grazing regimes or rainfall, and these variables may have interacted to influence detection probabilities (Broadley et al., 2019; Davis et al., 2021; Povlsen et al., 2023; Winter et al., 2005).…”

Using YOLO Object Detection to Identify Hare and Roe Deer in Thermal Aerial Video Footage—Possible Future Applications in Real-Time Automatic Drone Surveillance and Wildlife Monitoring

“…However, this method covered a relatively small area per flight, and required post-processing of the captured imagery, still making it time-consuming. In the present study, we tried a slightly different approach by manually piloting the UAV continuously, using the scouring method which also had been shown to match and potentially surpass the traditional spotlight method [9]. By scouring the area with the camera angled at about 45 • , we attained better situational awareness and covered a larger area per flight.…”

“…As the technologies advance and the price of these drones and sensors drops, they become more accessible to conservation biologists, wildlife managers, and other professionals working with wildlife monitoring [2][3][4][5]. The prospects of drones in wildlife monitoring have already been proven to save time, create better imagery and spatial data for especially cryptic and nocturnal animals [8,9], and reduce the risks and hazards for the observer [10,11]. However, the methods are still in the early stages, and need further development to be truly superior and cost-saving compared to traditional monitoring methods.…”