Managing vertebrate pest Sambar Deer at low abundance in mountains

Abstract

Summary Invasive 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.

Aerial culling invasive alien deer with shotguns improves efficiency and welfare outcomes

“…Aerial culling can be an effective, rapid, and humane means for removing large numbers of alien deer (Husheer and Robertson 2005;Bengsen et al 2022;Pulsford et al 2023), alien pigs (Cox et al 2022;Hamnett et al 2023), and other pest species in vast, remote, and inaccessible landscapes. In 2020, 2021, and 2022, South Australia's aerial culling programs have removed approximately 3,000 alien deer per year (BDO Econ-Search 2022).…”

“…Program costs and efficiency will vary with location and density of deer. For example, the cost of targeting sambar deer at low densities in alpine environments exceeded $1,000 deer -1 (Pulsford et al 2023). We compared 11 aerial culling programs that varied in location, planning, staffing, and logistic requirements.…”

“…Adopting new technologies could enhance the efficiency of aerial programs and welfare outcomes for target animals. Recently, Pulsford et al (2023) concluded that thermal-assisted aerial culls were more effective than ground shooting when targeting sambar deer, and Cox et al (2022) demonstrated improvements in both efficiency and welfare outcomes for fallow deer by incorporating thermal technology into their aerial programs. Government programs across Australia are trialling new combinations of firearms for different terrain and species of deer to improve the efficiency of culling operations.…”

Aerial culling feral fallow deer with shotguns improves efficiency and welfare outcomes

“…Adopting new technologies could enhance the efficiency of aerial programs and welfare outcomes for target animals. Recently, Pulsford et al (2023) concluded that thermal-assisted aerial culls were more effective than ground shooting when targeting sambar deer, and demonstrated improvements in both efficiency and welfare outcomes for fallow deer by incorporating thermal technology into their aerial programs. Government programs across Australia are trialling new combinations of firearms for different terrain and species of deer to improve the efficiency of culling operations.…”

“…P3, P4, and P5 are separate components of a large program. All costs in AU$ and include goods and services tax.Aerial culling can be an effective, rapid, and humane means for removing large numbers of feral deer(Bengsen et al 2022;Husheer and Robertson 2005;Pulsford et al 2023), feral pigs(Cox et al 2022), and other pest species in vast, remote, and inaccessible landscapes. Over the last three years, South Australia's aerial culling programs have removed approximately 3,000 feral deer per year (BDO EconSearch 2022).…”