Managing vertebrate pest Sambar Deer at low abundance in mountains

Abstract

SummaryInvasive species such as vertebrate herbivores cause threats to native ecosystems through causing changes to vegetation composition and structure, competition, ecosystem engineering, impacts on soil, and through spreading disease. In the mountainous country of Australia, Sambar Deer (Rusa unicolor) are becoming an increasing threat to fragile and endangered ecosystems, which are also facing other significant threats such as climate change. Methods for ameliorating these impacts are currently limited to lethal control programmes through shooting or fencing key areas. Fencing is not a viable option for large areas and can have large logistical costs as well as negative ecological outcomes. This study aimed to compare two shooting methods (ground shooting vs thermally assisted aerial culling with thermal image operator) for controlling sambar at low densities in a mountainous area. This programme was the first to use this specific thermal technique for deer in mountainous country in Australia. We found that thermally assisted aerial culling was more effective for removing Sambar than ground shooting. Thermally assisted aerial culling removed more Sambar in total, shot more animals per hour, covered a larger search area, was cheaper per hectare covered, and had very high “seen”, “targeted”, and “shot” ratios. Ground shooting sessions were lower in cost overall, but the cost per hectare was higher and rate of Sambar shot was lower than that of thermally assisted aerial culling. Ground shooting did remove more Sambar per hectare as ground shooting focuses on a smaller area, but this advantage is outweighed by the fact that thermally assisted shooting also allowed the concurrent removal of Feral Pigs. This work indicates that thermally assisted aerial culling is the preferred method for effective management of Sambar in an alpine environment. Ground shooting may be beneficial when Sambar are concentrated in key areas or to complement initial knock down by thermally assisted aerial culling.