Effectiveness and costs of helicopter-based shooting of deer
Andrew J. Bengsen
A , David M. Forsyth A * , Anthony Pople B , Michael Brennan B , Matt Amos B , Mal Leeson C , Tarnya E. Cox A , Bec Gray D , Ollie Orgill E , Jordan O. Hampton F H , Troy Crittle D and Kym Haebich G
+ Author Affiliations
- Author Affiliations
A Vertebrate Pest Research Unit, NSW Department of Primary Industries, 1447 Forest Road, Orange, NSW 2800, Australia.
B Biosecurity Queensland, Queensland Department of Agriculture and Fisheries, 41 Boggo Road, Dutton Park, Qld 4102, Australia.
C Local Land Services Regional Operations, 112 Market Street, Mudgee, NSW 2850, Australia.
D Biosecurity and Food Safety, NSW Department of Primary Industries, 4 Marsden Park Road, Calala, NSW 2340, Australia.
E Environment, Planning and Sustainable Development Directorate, ACT Government, Sanford Street, Mitchell, ACT 2911, Australia.
F Ecotone Wildlife, PO Box 76, Inverloch, Vic. 3096, Australia.
G Limestone Coast Landscape Board, 61 Anzac Terrace, Keith, SA 5267, Australia.
H Present address: Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Parkville, Vic. 3052, Australia.
Wildlife Research 50(9) 617-631 https://doi.org/10.1071/WR21156
Submitted: 29 October 2021 Accepted: 14 April 2022 Published: 6 July 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
Context: Helicopter-based shooting has been widely used to harvest deer or control overabundant populations in Australasia, but the effectiveness and cost of this method as a deer control tool has seldom been evaluated.
Aims: We evaluated the effectiveness and costs of helicopter-based shooting of fallow deer (Dama dama) and chital deer (Axis axis) in eastern Australia by quantifying (1) reductions in density, (2) the relationship between numbers killed per hour and deer density (i.e. the functional response), (3) the costs of control and (4) the effort–outcome and cost–outcome relationships.
Methods: We evaluated the costs and effectiveness of 12 aerial shooting operations aiming to reduce fallow deer (n = 8) or chital deer (n = 4) population densities at nine sites in eastern Australia. Sites were characterised by fragmented woodland, and all but one operation aimed to reduce grazing competition with livestock. We used pre-control population density estimates and operational monitoring data to estimate the costs and outcomes of each operation. We combined data from all operations to estimate the relationship between shooting effort and population reduction, as well as costs associated with different levels of effort.
Key results: Population reductions for operations ranged from 5% to 75% for fallow deer, and from 48% to 88% for chital deer. The greatest population reductions occurred when effort per unit area was greatest, and the largest reductions in deer density occurred when shooting was conducted in consecutive years. The functional response of hourly kills to deer density was best described by a modified Ivlev model, with the asymptotic kill rate estimated to be 50 deer per hour. There was no support for the existence of a prey refuge, that is, a threshold population density below which no deer could be shot. Helicopter charter was the primary cost of helicopter-based shooting programs, followed by labour; firearm and ammunition costs were relatively minor.
Conclusions: Helicopter-based shooting can rapidly reduce deer populations over large geographic areas, but the magnitude of the reduction depends on the effort (hours of shooting) per deer per km2.
Implications: Aerial shooting operations should include a pre-control population survey so that (1) measurable objectives can be established, (2) the likely level of effort and cost required for objectives to be met can be estimated and planned for, and (3) the realised population reduction can be estimated.
Keywords: abundance, aerial gunning, aerial shooting, aerial survey, Bayesian statistics, chital deer, culling, density, effort–outcome, fallow deer, functional response, mark–recapture distance sampling.
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