Rapid eradication of invasive rusa deer (Cervus timorensis) from Wild Duck Island, Australia, using thermally assisted aerial culling and a camera trapping grid

Abstract

Non-native rusa deer ( Cervus timorensis ) were introduced to the 380-ha Wild Duck Island, an important flatback turtle nesting site in Broad Sound Islands National Park, Queensland, Australia, in the mid-2000s. Initial attempts to remove the population through ground and aerial culling (2007–2017) were unsuccessful. A more comprehensive eradication program commenced in 2018, employing aerial culling. In late 2019, a grid of 44 motion-sensitive cameras was established to estimate deer population size and map its distribution. During 2018–2023, 168 rusa deer were culled. As the population declined, the hours flown per deer culled increased. To efficiently remove the remaining deer, a thermal imager was used in 2022, helping to remove 10 of the last 11 deer. In January 2023, the camera grid detected one remaining adult female, which was detected by the thermal imager and culled in August 2023 after only 28 min of flying. Subsequent monitoring over 4,094 trap days revealed no deer presence. Modelling of camera grid data indicated a 99.3% probability of eradication (95% C.I. 0.973–0.999), and no further signs of rusa deer have been observed during opportunistic searches. To the best of our knowledge, this is the first documented eradication of a non-native rusa deer population. Key factors enabling success included transitioning from ground-based to helicopter-based shooting and integrating thermal imaging to locate and remove the last 11 individuals. A robust monitoring program tracked progress towards eradication and enabled the probability of eradication to be estimated. The approach used in this project could be applied to other programs aiming to eradicate cryptic large mammals.