Using Drones with Thermal Imaging to Estimate Population Counts of European Hare (Lepus europaeus) in Denmark

Abstract

Drones equipped with thermal cameras have recently become readily available, broadening the possibilities for monitoring wildlife. The European hare (Lepus europaeus) is a nocturnal mammal that is closely monitored in Denmark due to populations declining since the mid-1900s. The limitations of current population-assessment methods, such as, spotlight counts and hunting game statistics, could be overcome by relying on drone surveys with thermal imaging for population counts. The aim of this study was to investigate the use of a DJI Mavic 2 Enterprise Advanced drone with thermal imaging as a tool for monitoring the Danish hare population. Multiple test flights were conducted over agricultural areas in Denmark in spring 2022, testing various flight altitudes, camera settings, and recording methods. The test flights were used to suggest a method for identifying and counting hares. The applied use of this methodology was then evaluated through a case survey that had the aim of identifying and counting hares over an agricultural area of 242 ha. Hares could be detected with thermal imaging at flight altitudes up to 80 m, and it was possible to fly as low as 40 m without observing direct behaviorial changes. Thermal images taken at these altitudes also provided enough detail to differentiate between species, and animal body size proved to be a good species indicator. The case study supported the use of thermal imaging-based drone surveys to identify hares and conduct population counts, thus indicating the suggested methodology as a viable alternative to traditional counting methods.

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).…”

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

“…Recent technological advances, such as better battery capacity, improved sensors, and lower cost, have accelerated the applications of aerial drones, also known as uncrewed or unmanned aerial vehicles (UAV), unmanned aerial systems (UAS) and remotely piloted aircraft systems (RPAS), in the field of ecology and wildlife monitoring [22][23][24][25][26][27][28][29][30]. Especially multirotor drones, as opposed to fixed-winged drones, equipped with thermal infrared (TIR) cameras have proven to be a useful tool for monitoring cryptic and nocturnal species, on par with spotlight methods [3,25,26,[30][31][32][33][34][35][36][37][38].…”

“…Their study also suggested that angles other than 90 • of the drone-mounted sensors during surveys should be examined [35,39]. Povlsen et al [24] conducted a drone survey concurrently with a spotlight count. This was performed by flying at a 60 m altitude, with the camera recording directly downwards, while the drone was flying autonomously in a predetermined flight path, covering the same transects surveyed with spotlights.…”

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

“…Povlsen et al [28] flew in predetermined flight paths at 60 m altitude with a DJI Mavic 2 Enterprise Advanced with the thermal camera pointing directly down (90 • ), covering the transects that were simultaneously surveyed, monitoring hare, deer, and fox. Using transect counting, it was possible to spot roughly the same number of animals as the traditional ground-based spotlight count [28]. However, this method covered a relatively small area per flight, and required post-processing of the captured imagery, still making it time-consuming.…”