Research Article |
Corresponding author: Corey J. A. Bradshaw ( corey.bradshaw@flinders.edu.au ) Academic editor: Sandro Bertolino
© 2023 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.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Bradshaw CJA, Doube A, Scanlon A, Page B, Tarran M, Fielder K, Andrews L, Bourne S, Stevens M, Schulz P, Kloeden T, Drewer S, Matthews R, Findlay C, White W, Leehane C, Conibear B, Doube J, Rowley T (2023) Aerial culling invasive alien deer with shotguns improves efficiency and welfare outcomes. NeoBiota 83: 109-129. https://doi.org/10.3897/neobiota.83.100993
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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 We also compared program costs and efficiency against published and unpublished data from ten other aerial-culling programs for alien deer in South Australia since 2009.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.
Aerial culling, animal welfare, Australia, cost-effectiveness, costs, culling, Dama dama, helicopters, invasive alien species, management, non-native species, shooting, wildlife
Invasive alien deer (known in Australia as ‘feral deer’; hereafter, ‘alien deer’) are some of Australia’s worst emerging pests. The total number of deer in Australia increased from an estimated 200,000 in 2000 (
Australia has six species of alien deer – fallow (Dama dama), red (Cervus elaphus), hog (Axis porcinus), chital (A. axis), rusa (C. timorensis), and sambar (Rusa unicolor); of all the alien deer species in the country, fallow deer are the most abundant and widespread (
Adopting new technologies could enhance the efficiency of aerial programs and welfare outcomes for target animals. Recently,
Fallow deer are also the most abundant deer species in South Australia and the population is increasing despite the Government of South Australia supporting helicopter and ground-based shooting programs for more than 15 years. Recently, the State Government and Regional Landscape Boards launched a four-year program to reduce the populations of alien fallow deer in South Australia. The program focusses on coordinating landscape-scale aerial culls and aims to deliver the most efficient and humane approach to aerial culling. In that context, the State Government recently did a trial program (henceforth, ‘P1’) to test a new approach to aerial culling; it incorporated advanced thermal technology and a second shooter with a shotgun to target alien fallow deer.
Our study assessed the outcomes from P1 to examine the efficiency of the shotgun-rifle-thermal configuration compared to other configurations used in aerial culling programs delivered in the same region and across South Australia. We predicted that using the shotgun-rifle-thermal combination could: (i) improve animal welfare outcomes for target animals by minimising time between first shot with a shotgun and apparent death and pursuit time, and rapidly deliver fatal injuries to vital organs; and (ii) increase the efficiency and/or cost-effectiveness of the program compared to other programs delivered in the same region and across the State.
The aerial culling trial program P1 occurred from 1–7 in October 2022, covering ~ 20,000 ha of private property in the Limestone Coast region of South Australia, about 300 km southeast of Adelaide (Fig.
All programs used either an AS350 B2 ‘Squirrel’ (Airbus Helicopters, France) or Robinson R44 (Robinson Helicopter Company, U.S.A.) helicopter flown at altitudes generally below 250 m above sea level for all shooting operations. Shotguns can be used up to a maximum of 25 m from the target animal, so helicopters typically remained at 15–20 m above ground level at time of shooting. While rifles have a longer maximum range, shooters in the programs we describe do not typically take rifle shots at distances > 30 m from the target animal.
In P1, one shooter (hereafter, the ‘primary’ shooter) was equipped with a Benelli M2 semi-automatic shotgun with a 26" barrel and a custom choke at full extension, which created a 25-cm pellet spread at 20 m and a 45-cm spread at 30 m. The primary shooter targeted deer in open areas, within a 30-m range. The shotgun was fitted with a red-dot scope (Sightron S30-5 and Aimpoint 9000L); it had a 12-shell tube magazine and was loaded with GB SSG 21-pellet buckshot and Winchester Super-X 16-pellet buckshot. The projectiles of the 21-pellet SSG cartridges have an average weight of 1.8 g, with an average total payload of 37 g. The projectiles in the Winchester Super-X 16-pellet SSG cartridges have an average weight of 2.3 g and a total payload of 36 g. Professional shooters (Wildlife Resources Australia, Wangaratta, Victoria) did not observe any difference in the performance between the different rounds of buckshot. Both round types were mixed into the primary shooter’s ammunition bags, and we did not distinguish between ammunition type during data collection. The primary shooter was positioned in the rear right-hand side of the helicopter behind the pilot (Fig.
Seating configuration of the helicopter crew in P1 A pilot B secondary shooter with rifle and thermal scope C thermographer, and D primary shooter with shotgun and red-dot scope. Yellow and blue polygons show the indicative field of view for the shooters, and the green polygon shows the field of view for the thermographer.
Another shooter (‘secondary’ shooter) was equipped with a Wedgetail WT25 semi-automatic, .308-calibre rifle with a variety of ammunition types. The ammunition included 160-grain copper projectiles used to cull deer near wetlands and creeks. Copper projectiles are being trialled in many pest-control programs in Australia because they do not contain any lead, but they could potentially increase the risk of ricochet (Steven Hess, U.S. Department of Agriculture, Animal and Plant Health Inspection Service, National Wildlife Center, Colorado, personal communication). The secondary shooter targeted deer within vegetated areas and had a range of 70 m. The secondary shooter was positioned next to a thermal camera operator (‘thermographer’; Fig.
Shooters made chest shots exclusively. For small deer species, especially those that move quickly and erratically such as fallow deer, chest shots are preferred for the best welfare outcomes (
All seating configurations and helicopter operational procedures are obliged to conform to the “Civil Aviation Safety Regulations 1998” and “Manual of Standards” produced and overseen by the Commonwealth of Australia’s Civil Aviation Safety Authority (casa.gov.au). Safety therefore has primacy over all other considerations, including animal humaneness and efficiency/cost components of aerial shooting.
All P1 flights were recorded on the thermal camera and with a GoPro 3 camera. The thermal camera captured all vision from the thermographer’s perspective. The GoPro 3 camera was mounted to the rear firewall of the helicopter and recorded continuously; it captured the activities of all personnel in the helicopter and most of their field of view (Fig.
A GoPro 3 camera, mounted to the rear firewall of the helicopter, captured the seating configuration of the personnel in the helicopter, their field of view, and four deer being pursued (circled in red).
Based on the approach described by
To test which components of an individual kill explained the most variation in the time from the start of the pursuit to apparent death, we constructed a series of generalised linear models using the glm function in the stats R library (
After the morning flights on 4 and 5 October 2022, 20 deer carcasses were located for assessment. Field dissections were done to collect information on shotgun-pellet penetration and spread and organ damage. Shotgun injuries were determined by cutting and peeling back the pelt and visually assessing the external muscle tissue for bruising and penetration of shotgun pellets on the impact and exit sides. Because damage from multiple projectiles to either the heart or lungs is lethal, the number of projectiles that impacted the thorax was also recorded for each carcass.
Following inspection of the muscle tissue and sites of pellet impact, the chest cavity was opened below the sternum using a bone saw. The heart and lungs were removed and inspected for tissue damage, wound channels, bleeding, and blood coagulation to determine whether pellets penetrated the heart and/or the lungs. The heart and lungs were dissected to establish the extent of the wounding by shotgun pellets, if not obvious externally. The chest cavity was also inspected for pooling of blood. All damage was recorded photographically, and the sites assessed for evidence of struggle or distress (such as kicking or disturbance of surrounding ground).
We compared the economic costs and outcomes of P1 to those of 10 other aerial culling programs (P2–P11) completed between June and November 2022. All programs targeted deer in the same region (Limestone Coast) or elsewhere in South Australia, and varied in crew configuration, firearms, equipment, deer density, area covered, and landscape (Table
Summary details of 11 alien deer aerial culling programs, including the recent trial (P1), to compare program efficiency. F = fallow deer (F); R = red deer (R); S = sambar deer (S); TAAC = thermal-assisted aerial cull (crew has a dedicated thermographer). All programs used .308 centrefire rifles exclusively except for P1 and P5 that also used a shotgun. The lead South Australian Government agency for each program was: PIRSA (P1–P5); Hills and Fleurieu Landscape Board (P6–P7); Limestone Coast Landscape Board (P8–P9); Eyre Peninsula Landscape Board (P10–P11).
No. | Region and location | Land use | Area (km2) | Deer species | Deer density | Helicopter | Primary shooter | Secondary shooter | TAAC | Shotgun | Notes |
---|---|---|---|---|---|---|---|---|---|---|---|
P1 | Limestone Coast, Willalooka | rich agricultural area, isolated patches of vegetation | 150 | F, R, S | high | B2 Squirrel | √ | √ | √ | √ | current trial; fallow most common species |
P2 | Limestone Coast, Taratap | coastal agricultural area, linear vegetation remnant and dunes | 100 | F, R | high | B3 Squirrel | √ | √ | first trial of TAAC for deer in South Australia; fallow most common species | ||
P3 | Fleurieu Peninsula, Parawa | undulating peri-urban area mixed agricultural/rural with abundant vegetated creek lines and vegetation pockets | 60 | F | high | B2 Squirrel | √ | √ | Programs 3-5 delivered as part of a single program, but separated based on crew configuration, area covered, firearm type | ||
P4 | Fleurieu Peninsula, Parawa | 30 | F | high | B2 Squirrel | √ | √ | √ | |||
P5 | Fleurieu Peninsula, Parawa | 110 | F | high | B2 Squirrel | √ | √ | √ | √ | ||
P6 | Adelaide Hills, Mt Bold | peri-urban water reservoir, undulating land covered in native and pine forest | 20 | F | high | R44 | √ | goats also targeted | |||
P7 | Fleurieu Peninsula, Deep Creek | national park – undulating landscape with thick vegetation | 40 | F | high | B2 Squirrel | √ | ||||
P8 | Limestone Coast, Salt Creek to Taratap | coastal agricultural area, linear vegetation remnant and dunes | 1200 | F, R, S | high | 2 × R44 | √ | 2 helicopters, single shooter in each; fallow most common species | |||
P9 | Limestone Coast, Salt Creek to Taratap | coastal agricultural area, linear vegetation remnant and dunes | 1200 | F, R, S | high | 2 × R44 | √ | 2 helicopters, single shooter in each; fallow most common species | |||
P10 | Eyre Peninsula, Buckleboo | open, dry-land cropping country, isolated vegetation patches | 160 | R | low | R44 | √ | no individual coordinates | |||
P11 | Eyre Peninsula, Chadinga | remote conservation reserve, squat coastal vegetation | 100 | no deer culled | low | R44 | √ | no individual coordinates |
Staff costs were included in the assessment because they are necessary to plan and deliver all aerial culling programs. This approach is consistent with ‘competitive neutrality’ requirements for government agencies in South Australia, which ensure government businesses compete fairly in the market (
To contextualise any landscape-scale differences among the programs that could have affected cost effectiveness, we also calculated the dominant landcover classes within the area of each program using the South Australia Land Cover raster (2010–2015) at a resolution of 25 m × 25 m (available from data.sa.gov.au/data/dataset/sa-land-cover). We compared the land cover classes in which kills occurred to ‘available’ land cover classes within a minimum convex polygon defined by the locations of all kills in the program. Additionally, we calculated the mean human population density (persons km-2) within 50 km of the program’s minimum convex polygon to assess the relative likelihood of human visitors to a program area during culls (when near to larger human populations, personnel costs increase – see Results).
We reviewed all available footage from P1, which included 20% of the 611 fallow deer culled (n = 104). Of these, 92% were killed with a shotgun only (n = 96) and 8% with a shotgun-rifle combination (n = 8). Shooters used a total of 383 shotgun rounds and 10 rifle rounds (Table
Summary statistics from footage of 104 deer killed with a combination of firearms, a secondary shooter, and thermal-imaging technology.
Summary statistic | Order of deer shot | ||||||
---|---|---|---|---|---|---|---|
Firsta | Second | Third | Fourth | Fifthb | Total | Mean | |
sample size (# deer) | 45 | 29 | 21 | 8 | 1 | 104 | – |
shotgun rounds fired | 169 | 114 | 64 | 34 | 2 | 383 | – |
mean ± s.e. shotgun rounds per deer | 3.8 ± 0.3 | 3.9 ± 0.3 | 3.0 ± 0.4 | 4.3 ± 0.6 | 2.0 | – | 3.7 ± 0.2 |
rifle rounds fired | 4 | 6 | – | – | – | 10 | – |
min-max time between first shot with shotgun and apparent death (seconds) | 2.9–35.9 | 2.6–32.0 | 2.6–33.2 | 4.0–14.1 | 3.1 | – | – |
mean ± s.e. time between first shot with shotgun and apparent death (seconds) | 12.5 ± 1.0 | 11.4 ± 1.3 | 9.2 ± 1.5 | 7.9 ± 2.4 | 3.1 | – | 11.1 ± 0.7 |
min-max pursuit time (seconds) | 13.9–83.1 | 16.0–89.4 | 14.5–120.2 | 46.3–159.0 | 84.2 | – | – |
mean ± s.e. pursuit time (seconds) | 34.9 ± 5.2 | 50.7 ± 6.5 | 63.1 ± 7.6 | 87.4 ± 12.3 | 84.2 | – | 49.5 ± 3.4 |
The mean time between first shot with a shotgun and apparent death was 11.1 seconds (± 0.7; n = 104). Individual deer, or the first deer shot in a group, had the greatest mean time between first shot and apparent death, but this time decreased with subsequent individuals targeted within the group (Fig.
Mean time between first detection and apparent death was 49.5 seconds (± 3.4; n = 104). Pursuit time increased with subsequent deer shot within a group (Fig.
There was a positive effect of deer group size and number of shotgun rounds fired on the total time elapsed since start of pursuit to death (Table
Generalised linear model results testing the effects of time between first and last/kill shots (t1stLast), number of rounds fired (rnds), and group size (grpSize) on the time from the start of the pursuit to the kill with a shotgun (response). k = number of model parameters; ℓ = -log likelihood; AICc = Akaike’s information criterion corrected for small sample size; wAICc ≈ model probability; %DE = percent deviance explained.
Model | k | ℓ | AIC c | wAICc | %DE |
---|---|---|---|---|---|
~grpsize + rnds | 3 | -24.770 | 57.945 | 0.529 | 42.7 |
~t1stLast + grpSize + rnds | 4 | -23.859 | 58.330 | 0.436 | 43.7 |
~t1stLast + grpSize | 3 | -27.489 | 63.383 | 0.035 | 39.7 |
~grpSize | 2 | -32.480 | 71.201 | 0.001 | 33.8 |
~rnds | 2 | -50.879 | 107.997 | <0.001 | 6.9 |
intercept-only | 1 | -54.745 | 113.610 | <0.001 | - |
~t1stLast + rnds | 3 | -50.356 | 109.116 | <0.001 | 7.8 |
~t1stLast | 2 | -54.603 | 115.446 | <0.001 | 0.3 |
The 20 carcasses were recovered and dissected within six hours of being culled in P1. All carcasses had received shotgun wounds only and were located using GPS data collected during the flight. A total of 116 shotgun pellets had penetrated the thorax of the 20 deer (5.8 ± 0.6 pellets deer-1; range: 3–13 pellets deer-1). Lethal lung-penetrating wounds were recorded in all 20 animals; 14 (70%) also recorded lethal heart-penetrating wounds. The wounds and their classification are shown in Suppl. material
For 2022, the cost of delivering 11 aerial culling programs for alien deer in South Australia exceeded $1.1 million (Table
Cost summary for 11 deer culling programs completed in South Australia between June and November 2022. P3, P4, and P5 are separate components of a large program; all staff hours were costed at $150 per hour. All costs in AU$ and include goods and services tax.
Detailed costs | P1 | P2 | P3 | P4 | P5 | P6 | P7 | P8 | P9 | P10 | P11 |
---|---|---|---|---|---|---|---|---|---|---|---|
helicopter operations | 81,999 | 46,620 | 52,851 | 28,959 | 83,257 | 28,216 | 27,390 | 104,247 | 106,904 | 28,875 | 14,300 |
ammunition | 7,500 | 1,868 | 2,802 | 1,535 | 4,413 | 2,756 | 2,200 | 4,051 | 3,221 | 0 | 0 |
professional shooters | 7,200 | 3,000 | 3,842 | 2,105 | 6,053 | 6,916 | 4,500 | 27,000 | 27,000 | 4,200 | 1,780 |
PIRSA costs | 20,625 | 26,149 | 18,010 | 9,869 | 28,371 | 6,450 | 0 | 0 | 0 | 0 | 0 |
Landscape board costs | 5,625 | 970 | 1,890 | 701 | 2,659 | 29,100 | 21,375 | 16,950 | 9,000 | 31,000 | 6,750 |
NPWS costs | 0 | 0 | 750 | 0 | 900 | 11,600 | 23,415 | 0 | 0 | 450 | 750 |
DEW costs | 0 | 0 | 0 | 0 | 0 | 0 | 655 | 1172 | 1609 | 0 | 0 |
SA Water costs | 0 | 0 | 0 | 0 | 0 | 47250 | 0 | 0 | 0 | 0 | 0 |
Forestry SA costs | 0 | 0 | 2,500 | 1,500 | 3,000 | 0 | 0 | 0 | 0 | 0 | 0 |
community engagement | 2,500 | 2,710 | 2,401 | 1,316 | 3,783 | 1,800 | 2,250 | 0 | 0 | 2,550 | 1,575 |
other logistics (car hire, travel, food, etc.) | 4,700 | 2,460 | 2,145 | 1,175 | 3,379 | 1,900 | 2,600 | 6,846 | 6,978 | 3,100 | 2,200 |
Total costs | $130,149 | $83,777 | $87,190 | $47,160 | $135,816 | $135,988 | $84,385 | $160,266 | $154,712 | $70,175 | $27,355 |
Operating staff costs accrued by various agencies (South Australian Department of Primary Industries and Regions; Regional Landscape Boards of the Hills and Fleurieu, Limestone Coast, and Eyre Peninsula; National Parks and Wildlife Service; Department for Environment and Water; SA Water; Forestry SA) varied considerably among programs. These costs were largely associated with the location of the operations. P3–P7 occurred on public lands (e.g., parks) near metropolitan areas, so additional staff were required to supervise entrances and prevent public access during the operations. Staff costs for all agencies for all programs combined exceeded $330,000, or 30% of all costs. P6 had the highest staff costs, exceeding $45,000, which comprised 54% of all costs associated with the project. This program required many multi-agency staff to supervise gates and entrances to the operations area, which is a high-profile, peri-urban site on public land (Fig.
From the 11 programs, a total of 3,609 deer (at least 90% fallow deer) were culled during 486 flight hours (see Table
Cost effectiveness of 11 alien deer culling programs done in South Australia between June and November 2022. P3, P4, and P5 are separate components of a large program. All costs in AU$ and include goods and services tax.
Program outcomes | P1 | P2 | P3 | P4 | P5 | P6 | P7 | P8 | P9 | P10 | P11 |
---|---|---|---|---|---|---|---|---|---|---|---|
total animals culled | 655 | 190 | 195 | 179 | 645 | 347a | 243 | 645 | 503 | 7 | 0 |
total flight hours | 26 | 16 | 18 | 10 | 29 | 20 | 10 | 87 | 90 | 21 | 9 |
animals/flight hour | 25 | 12 | 11 | 18 | 22 | 17 | 24 | 7 | 6 | < 1 | 0 |
cost/animal | $198.70 | $440.93 | $447.13 | $263.46 | $210.57 | $391.90d | $347.26 | $248.47 | $307.58 | $10,025 | - |
cost/flight hour | $4,948.63 | $5,404.97 | $4,777.58 | $4,716.00 | $4,724.05 | $6,799.40 | $8,438.50 | $1,842.14 | $1,719.02 | $3,341.67 | $3,073.60 |
cost/area (km2) | $867.66 | $837.77 | $1,453.17 | $1,572.00 | $1,234.69 | $6,799.40 | $2,109.63 | $133.56 | $128.93 | $483.59 | $273.55 |
dominant vegetation in program area | dry cropland | dry cropland | dry cropland | dry cropland | dry cropland | woody native > 1 m | woody native > 1 m | dry cropland | dry cropland | woody nativec > 1 m | woody natived > 1 m |
dominant vegetation in which deer were culled | dry cropland | woody native > 1 m | woody native > 1 m | woody native > 1 m | woody native > 1 m | woody native > 1 m | woody native > 1 m | woody native > 1 m | woody native > 1 m | ||
mean human pop density within 50 km (persons km-2) | 0.47 | 0.52 | 69.70 | 75.76 | 68.64 | 58.05 | 59.50 | 4.71 | 3.96 | 0.10 | negligible |
Deer were most commonly killed in native woody vegetation > 1 m in height (64% of all kill locations across all programs) (Table
Aerial culling can be an effective, rapid, and humane means for removing large numbers of alien deer (
Unfortunately, a large proportion of the population of alien deer must be removed each year to drive population decline. For example, at least 34% of the population of fallow deer must be removed each year just to avoid population increase, and even higher culling proportions are required for other deer species (hog: 52%; chital: 49%; rusa: 46%; sambar: 40%) (
Large-scale, intensive, and coordinated control programs are therefore necessary to drive population declines of alien deer. Improved efficacy of aerial culling programs is clearly needed if management goals to arrest the impacts of deer are to be realised. However, the adoption of new approaches and technologies first requires examination to ensure high animal welfare standards are met, in addition to operational cost effectiveness. Analysis of the outcomes from a recent trial program that used shotguns and thermal equipment, in combination with a rifle, provided insight into the humaneness and effectiveness of a new approach to controlling alien deer in South Australia.
In pest control operations, welfare is generally evaluated in terms of the duration and intensity of suffering (
Individual deer, or the first deer shot in a group, had the longest mean time between first shot and apparent death, and this interval decreased if targeting subsequent individuals in a group. This decrease is because of the relatively longer time taken to pursue a group of deer after first being sighted, before the first deer is shot. Once the group of deer was engaged, the pursuit time of the remaining deer in the group was usually shorter. The maximum time recorded between first shot and apparent death for any deer was 35.9 seconds, which is an improvement on programs that have used a rifle exclusively (
Unlike
Other influences such as proficiency of shooters, type of helicopter used, and weather conditions will also affect time between first shot (with shotgun or rifle) and death. In their study,
In most jurisdictions, procedures and guidelines for aerial culling programs of alien deer dictate that a shot with a rifle is not taken until the shooter has a clear shot of the chest or head, and that there is no risk of a wounded animal escaping to somewhere where a follow-up shot cannot be taken. The spread pattern of the shotgun pellets requires less precision for pellets to hit the thorax of the animal. Hence, using a shotgun reduces the time required to ‘line up’ an accurate and humane shot.
In terms of the intensity of suffering, all animals assessed had received rapid and lethal impacts from shotgun pellets. The average number of thorax-penetrating wounds delivered with the shotgun was higher than in some autopsies of deer culled with a rifle (
A potential shortcoming of our study is that the apparent death of the target animals in P1 was assessed in the air by the pilot, and at least one other crew member, rather than landing the helicopter to have a veterinary surgeon make a formal assessment (e.g.,
Helicopter-based aerial shooting is a cost-effective tool for alien deer control (
The largest expense associated with aerial culling is helicopter flight time (
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 (
We found that the use of a suitable shotgun could improve welfare outcomes for culled deer, compared to programs that used .308-calibre rifles only. Improved welfare outcomes included reduced pursuit time and reduced time between the first shot and death. Furthermore, all deer dissected were shot more than once, and received multiple thorax-penetrating wounds, resulting in lethal injuries to either the lungs and/or heart, and ensuring a short time until death. These findings are at least as good as the best welfare outcomes reported from aerial culling programs in Australia to date (e.g.,
We found that a two-shooter crew configuration, with the addition of a thermal camera operator and a primary shooter with a shotgun, resulted in increased operational efficiency and cost effectiveness when compared to more conventional crew configurations. These changes to the format of the aerial operation appeared to increase efficiency independently, but the addition of the shotgun appears to have made the biggest single difference. These results are likely to be applicable to areas with similar deer densities, canopy cover, and terrain to the Limestone Coast region of South Australia. Although thermal imagery can increase detection of control targets in denser vegetation, relative openness of the canopy will always be required for shooting to be efficient and effective. Control options that deliver improved animal welfare outcomes and increased efficiencies are urgently needed to manage expanding populations of alien deer in South Australia.
We thank M. Garrod, W. Boardman, D. Evans, I. Hough, and A. Wiebkin for reviewing and improving drafts. We also thank D. Forsyth and A. Bengsen for their leadership in assessments of cost effectiveness for deer culling through the Centre for Invasive Species Solutions (invasives.com.au), of which Primary Industries and Regions South Australia (A.S., B.P., M.T., K.F., L.A.) is a member. We thank S. C. Hess for constructive review comments. All aerial culling programs were completed as part of ongoing pest animal management operations, which do not require animal ethics approval. The Primary Industries and Regions South Australia animal ethics Teaching, Research and Experimentation licence number is 176.
Supplementary information
Data type: figures
Explanation note: Deer VI, killed with the shotgun; pelt is removed to show the difference between shotgun-pellet wounds on the entry (A) and exit (B) sides of the carcase. Deer XV, showing typical wounds and mode of death for feral fallow deer culled with shotguns in this trial. Deer IX, showing typical wounds and mode of death for feral fallow deer culled with shotgun in this trial. Deer XII, showing typical wounds and mode of death for feral fallow deer culled with shotgun in this trial. Deer XIV, showing typical wounds and mode of death for feral fallow deer culled with shotgun in this trial. Proportion of feral deer killed per major land cover class (black bars) relative to availability (proportional coverage within a minimum convex polygon defined by the kill locations per program; green bars) for (a) all kill locations combined and (b–j) P1–P9. Mean human population density within 50 km of the minimum convex polygon defined from kill locations per program (top panel).