An assessment of thermal detection in aerial culling of feral deer and pigs in northern Australia

Context Aerial culling can be a highly effective method for reducing populations of medium to large herbivores such as feral pigs (Sus scrofa) and deer (e.g. chital, Axis axis). In temperate Australia thermal cameras can improve the detection of animals and therefore the efficiency of aerial culling programs. In a warmer climate the thermal contrast between mammals and their surrounding environment will be less marked. The benefits of thermal detection in aerial culling under these conditions needs to be assessed. Aims To quantify the efficiency (cost per animal removed) and effectiveness (culling rate) of thermal detection compared to conventional (unaided visual) approaches during aerial control of feral deer and pigs in a warm, tropical climate environment near Collinsville, Queensland, north-eastern Australia. Methods Data from video recordings taken during a chital deer control program were analysed to compare culling rates and animal detections between thermal and conventional shooting runs. Key results The thermal camera successfully detected animals under a variety of temperatures and in a range of canopy densities. The use of the thermal camera did not significantly increase the culling rate (number of animals removed h−1 or number of animals removed km−1) compared to conventional detection. There were no consistent differences in the time taken to detect animals (search time) across thermal or conventional runs. Conclusions Using thermal imagery is expected to provide significant gains in aerial culling rates over conventional detection when animal densities are lower and in dense canopy cover where animals are difficult to detect. Implications Selective use of thermal imagery in northern Australia could yield benefits in future culling programs, but further assessments are recommended to optimise control practices.