Evaluating aerial net gunning and chemical immobilisation for capture of invasive sambar deer (Rusa unicolor) and red deer (Cervus elaphus) in alpine Australia

Abstract

Context Deer species are expanding in distribution and abundance in Australia. There is increasing focus on the ecology of these species, but effective deer capture methods are needed for telemetry studies. Aims The aims of this study were to develop, assess and refine a helicopter-based capture technique for wild sambar deer (Rusa unicolor) and red deer (Cervus elaphus), based on trials in south-eastern Australia. Methods We captured and collared 14 sambar deer and five red deer in two operations in Kosciuszko National Park in 2021, using a combination of aerial net gunning and chemical immobilisation delivered via hand injection. Captured animals were fitted with GPS collars to track their movements and activity post-capture. Physiological measurements were recorded as a means of assessing responses to capture and to optimise animal welfare outcomes. Key results Twenty-two deer were pursued and captured, with a total mortality rate of 14% (n = 3). The frequency of mortalities decreased from the first operation (17%) to the second operation (10%), largely attributed to allowable helicopter pursuit times being reduced. Post-release movement data indicated that delayed mortality due to capture did not occur. Activity of collared deer was lowest immediately following collaring, suggesting the procedure caused short-term decreases in deer activity. Conclusions Aerial capture of wild sambar deer and red deer poses animal welfare risks, but these can be minimised through the refinement in net gunning and pharmacological procedures to minimise animal stress. Implications This study describes an effective method for the safe capture of sambar deer and red deer, which will assist future wildlife researchers to further refine helicopter-based capture protocols and to collect spatial ecology and survival information about these species.