DOI: 10.3897/neobiota.106.173542

Authors: Thomas Botterill-James, Robert Buck, Calum X. Cunningham, Michael M. Driessen, Christopher N. Johnson, Anthony Pople, David M. Forsyth

Abstract: Effective management of invasive species requires robust projections of how alternative management strategies influence long-term invasion outcomes, required effort, and associated trade-offs. We used a spatially explicit population model, linked with empirical data on aerial culling efficiency, to project (from 2023 to 2060) alternative management scenarios for limiting the spread and establishment of an invasive fallow deer (Dama dama) population in a high-value conservation area, the Walls of Jerusalem National Park (WJNP), Tasmania, Australia. We compared six feasible aerial culling scenarios that varied in the frequency (annual, biennial, or five-yearly) and spatial extent (broad versus concentrated management zones) of control, relative to a baseline scenario with no future management. Scenarios were evaluated in terms of their ability to limit deer occupancy and abundance within the WJNP, the cumulative presence of deer over time, the amount of management effort required, and population-level animal welfare outcomes. All management scenarios reduced deer invasion into the WJNP relative to no management, but strategies that applied culling across a broad spatial extent were consistently more effective than those targeting only high-density source areas. More frequent culling further improved outcomes, although gains were modest relative to changes in spatial extent. Strategies that combined broad-scale culling with annual or biennial frequency achieved the best balance between reducing invasion pressure and limiting management effort, while also resulting in fewer deer being culled overall. Complete exclusion of deer from the WJNP was achievable only under a more intensive strategy involving annual culling across a substantially expanded area, but this required a nearly four-fold increase in effort compared to the scenarios aimed at minimising, rather than eliminating, invasion. Our results highlight trade-offs between management effectiveness, effort, and welfare outcomes, and demonstrate how spatial population models coupled with operational data can support practical, evidence-based decisions for managing invasive species.

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DOI: 10.3897/neobiota.103.157791

Authors: Julia Witczuk, Stanisław Pagacz, Romain Alliod

Abstract: New Caledonia’s unique terrestrial habitats – primarily mountain rainforest and sclerophyll forest – face significant threats from invasive ungulates, particularly Javan deer (Rusa timorensis), introduced in the 19th century and now widespread. Since deer are an important game and food source for local communities, the management strategy aims to mitigate their detrimental impact on ecosystems while maintaining populations at levels that continue to support hunting. To achieve these objectives, effective and reliable population monitoring methods are essential. Unmanned aerial vehicles (drones) equipped with thermal sensors represent a potentially superior alternative to conventional ground-based methods for ungulate inventories, particularly in remote and difficult-to-access areas. In this study, we explored the feasibility of using a rotor-wing drone and a thermal camera to estimate the relative density of Javan deer in two protected areas: Domaine de Déva (7,319 ha) and Parc provincial des Grandes Fougères (8,098 ha). Visual line-of-sight flights were conducted after sunset at altitudes of 80 and 100 m above ground level, with the camera fixed at 40° or 0° angles. In Déva, we surveyed 10 sampling blocks, and in Grandes Fougères, 4 blocks (each ranging from 56 to 92 ha). In the predominantly open savanna area of Déva, the estimated relative population density was 116 deer/km2 (SE = 26.8), with some blocks exceeding 400 deer/km2. In contrast, in the dense canopy rainforest of Grandes Fougères, the relative density was 7 deer/km2 (SE = 2.8), with a local maximum of 18 deer/km2. Differences in deer counts between consecutive flights over the same blocks (with time gaps of less than 100 minutes) were minor, demonstrating that drone surveys are highly repeatable – an essential quality for a reliable population monitoring program. To detect a 25% population reduction with a statistical power of 0.8, surveying 10 sampling blocks was sufficient in the high deer density savanna area, whereas approximately 28 blocks would be required in the rainforest. The logistics of drone operations were relatively straightforward in the savanna; however, in the rainforest, we encountered practical difficulties, including a limited number of suitable take-off sites and restricted visibility due to the dense canopy cover. Despite these obstacles, the method proved to be an effective and efficient approach for monitoring deer populations in the challenging landscapes of New Caledonia.

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DOI: 10.3897/neobiota.83.100993

Authors: Corey J. A. Bradshaw, Andrew Doube, Annette Scanlon, Brad Page, Myall Tarran, Kate Fielder, Lindell Andrews, Steve Bourne, Mike Stevens, Penny Schulz, Tom Kloeden, Seb Drewer, Rob Matthews, Chris Findlay, Warren White, Craig Leehane, Brett Conibear, James Doube, Ted Rowley

Abstract: Invasive alien deer (known in Australia as ‘feral deer’; hereafter, ‘alien deer’) are some of Australia’s worst emerging pest species. Recently, the Government of South Australia launched a four-year program to reduce the populations of alien fallow deer (Dama dama). The program will focus on coordinating landscape-scale aerial culls and seeks to deliver the most efficient and humane approach to aerial culling. We sourced data from a recent program trialling a new approach to aerial culling that incorporated advanced thermal technology and a second shooter with a shotgun to target fallow deer. We reviewed available video and audio records of 104 deer culled in the program to assess efficiency and welfare outcomes. We collected information on the number of shotgun and rifle rounds fired per animal, time between first shot with a shotgun and apparent death, and pursuit time. We completed field dissections of 20 individuals targeted in the program to assess the lethality of wounds inflicted with shotgun pellets. We also compared program costs and efficiency against published and unpublished data from ten other aerial-culling programs for alien deer in South Australia since 2009. A total of 383 shotgun rounds and 10 rifle rounds were used on 104 fallow deer in the focal program. We documented strong improvements to animal welfare for alien deer targeted with shotguns. The mean (± standard error) time between first shot and apparent death with a shotgun was 11.1 ± 0.7 seconds; mean pursuit time between detection and apparent death was 49.5 ± 3.4 seconds. Pursuit time increased with subsequent deer controlled within a group; the maximum pursuit time for any individual was 159.0 seconds. All autopsied animals had received lethal wounds from shotgun pellets, with 100% receiving lung-penetrating damage and 70% also receiving heart-penetrating damage. While a program that uses a shotgun and rifle combined with a second shooter and thermographer can cost more to mobilise, the outcomes measured in cost deer-1 made it the most cost-effective approach of any program we assessed. Control options that deliver improved animal welfare outcomes and increase efficiency are desirable for managing expanding populations of alien deer in South Australia and elsewhere.

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