Wild animals harbour a diverse range of pathogens. In Europe and North America, cervids (Family Cervidae) can act as reservoirs for viral, prion, bacterial, and parasitic infections. Wild deer often inhabit agricultural land, therefore representing a biosecurity risk due to their potential ability to transmit diseases to livestock. Multiple studies have investigated the infection status of wild deer in Australia, mostly during the 1970s and 1980s, and deer populations have increased greatly in abundance and distribution since then. Those studies provide an important baseline for the pathogens carried by wild deer in Australia but are limited by small sample size, the small number of deer species studied, and the disease detection methods used. Recent investigations using ELISA (Enzyme-Linked Immunosorbent Assay), PCR-based assays, and next-generation sequencing have substantially increased our understanding of viral and parasitic infections in Australian deer. These studies indicate that deer may act as reservoirs for pathogens such as Pestivirus, Neospora caninum and Entamoeba bovis. The use of next-generation sequencing has led to the discovery of novel viruses such as Picobirnavirus and a novel species of the genus Bopivirus, both of which pose transmission risks for domestic animals. Recent research confirms that wild deer could be a future source of viral and parasitic infections for domestic livestock and other wildlife species.

Context Vehicle-based shooting has been widely used to kill deer, but the animal-welfare outcomes of this technique have not been evaluated in Australasia.

Aim To assess the animal-welfare outcomes of peri-urban deer culling by quantifying the fates of deer seen and shot at, the duration of procedures, and the number and location of bullet wounds in deer.

Methods We assessed vehicle-based night shooting of peri-urban rusa deer (Cervus timorensis) by professional contractors in eastern Australia. Shooters targeted the heads of deer using .223 Remington^® rifles and 55 grain bullets. Independent veterinarians conducted ante-mortem (i.e. from the shooting vehicle) and post-mortem (i.e. inspecting the carcass) observations. The ante-mortem data were used to estimate the proportion of deer seen that were shot at, killed, wounded, and escaped. The influence of variables predicted to affect shooting outcomes was assessed. The numbers and locations of bullet wounds were recorded post-mortem.

Key results Of the 269 deer seen in 21 nights, 48% were shot at and 85% of those shot at were killed by either one (87%), two (10%) or three (3%) shots. The frequency of non-fatal wounding (i.e. escaping wounded) was 3.5% for those shot at and hit, and the median time to insensibility for the deer that were shot multiple times was 289 s. There was variation among shooters in their ability to hit a deer, and also to do so with a killing shot. The number of bullet wounds per deer ranged from 1 to 3 (mean = 1.1), with 83% of shots striking the brain and 17% striking the anterior skull, neck and jaw.

Conclusions The animal welfare outcomes we observed were comparable to those reported from other professional ground-based shooting programs for ungulates, but were poorer than those reported for professional ground-based shooting of peri-urban kangaroos.

Implications Our results suggest that one way to improve the animal welfare outcomes of vehicle-based shooting of peri-urban deer is by improving shooter training. Assessment of shooter performance should be a routine part of ground-based shooting programs.

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.

Aim 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.

Context In response to the toxic health threats posed by lead (Pb), there is currently a focus on transitioning to lead-free bullets for shooting wild animals.

Aim We aimed to quantify the killing efficiency and animal welfare outcomes of lead-based and lead-free (copper-based) bullets for ground-based shooting of sambar deer (Cervus unicolor) in Victoria, south-eastern Australia.

Methods We used shooter-collected data from recreational diurnal hunting and professional nocturnal culling during 2020–2021. Shooters recorded rifle calibre, cartridge type, bullet mass, bullet type, shooting outcomes (miss, wound or kill), shooting distance, flight distance (the distance between where the animal was shot and where it died) as an assumed positive correlate of time to incapacitation, anatomical zones struck by bullets, and frequency of bullet exit wounds. We used flight distance as our response variable, assuming that it is positively correlated with time to incapacitation. To examine the role of several predictor variables (including bullet type) potentially influencing flight distance, the dataset was reduced to those deer killed with a single thoracic shot.

Key results Our data captured shooting events involving 276 deer, with 124 deer shot at with lead-based bullets and 152 with copper-based bullets. Most (87%) of the deer were killed with a single shot. The frequency of non-fatal wounding was <4% for both bullet types and there was no distinct difference in the probability of a single shot kill for deer shot with either bullet type. For those deer killed with a single thoracic shot (n = 198), there was no evidence that bullet energy or shooting distance influenced flight distance. After accounting for differences in terminal kinetic energy, the mean flight distance of deer shot with lead-free bullets (35 m) was 56% greater than that of deer shot with lead-based bullets (22 m).

Conclusions Lead-based and lead-free bullets produced similar animal welfare outcomes for shooting sambar deer.

Implications A transition to lead-free ammunition for shooting sambar deer would have minimal impact on efficiency or animal welfare outcomes.

Context Introduced sambar deer (Cervus unicolor) are increasing in south-eastern Australia, and both volunteer and contract ground-based shooters are being used by management agencies to control their undesirable impacts. However, little is known about the effectiveness and costs of volunteer and contract shooters for controlling deer populations in Australia.

Aim We evaluated the effectiveness and costs of volunteer and contract ground-based shooters for controlling sambar deer and their impacts in a 5-year management program conducted in and around alpine peatlands in Alpine National Park, Victoria.

Methods Ground-based shooting operations were organised in two blocks. Within each block, four ~4200-ha management units were delimited, of which two were randomly assigned as treatment (ground-based shooting) and two as non-treatment (no organised ground-based shooting). In the treatment units, ground-based shooting was conducted using either volunteers or contractors. Each shooting team recorded their effort and the numbers of deer seen and shot, and used a GPS to record their track log and the time and locations of deer shot. Key costs were recorded for both shooter types.

Key results The catch per unit effort of contract shooters was four times greater than that of volunteer shooters. Both shooter types were most effective during the first half of the night and prior to sunrise, and when using a vehicle with a spotlight or walking with thermal-vision equipment. During the day, the use of gundogs to indicate deer significantly increased the success rate of volunteer shooters. Both volunteer and contract shooters used roads and tracks to move in the landscape, but contractors covered more ground than did volunteers. After accounting for key operational costs, the cost per deer killed was 10.1% higher for contract than volunteer shooters.

Conclusions The effectiveness of ground-based shooters is increased by operating at night using vehicles, spotlights and thermal-vision equipment. Contract shooters kill sambar deer at a faster rate, but are slightly more expensive per deer killed, than are volunteer shooters.

Implications Ground-based shooting is likely to be most effective when conducted at night with thermal-vision equipment, and in areas with a high density of roads and tracks.

Context Scent-trailing dogs (‘hounds’) are used to hunt introduced sambar deer (Cervus unicolor) in south-eastern Australia, but little is known about this recreational hunting technique.

Aim The aim of this study was to characterise hound hunting of sambar deer in Victoria, Australia. Our study had three objectives as follows: (1) to report the hunting success of the technique; (2) to estimate pursuit times and distances; and (3) to investigate the landscape features associated with kill sites.

Methods Data were collected from four hound-hunting crews during 2020–2021. GPS data from collars fitted to hounds were used to quantify hunt duration (min) and hunt distance (m). Logistic regression was used to estimate the effects of deer sex and hound pack size on the probability of hunting success. We used a Bayesian multinomial regression resource selection function (RSF) to identify the characteristics of sites where deer were killed (elevation, aspect, and distances to water and roads).

Key results The four hunting teams ranged in size from 2 to 10 people and from one to eight hounds. Of 136 hunts, most (88%) harvested a deer, with pursued deer escaping on the other 12% of occasions. Pursuit times and distances were highly variable, with pursuit time >60 min for 46% of hunts and pursuit distance >5 km for 30% of hunts. The probability of killing a pursued male and female deer were similar, and there was not a positive relationship between pack size and hunt success. The RSF showed that both male and female deer were more likely to be killed on steeper slopes and closer to roads.

Conclusions Successful hound hunting of sambar deer involves pursuits of considerable duration and requires a network of roads, with geographical features associated with deer kills sites being related to hunter access.

Implications Hound hunting may be a useful wildlife management tool for land managers, but further studies are needed to assess its efficacy for achieving management goals.

Context Introduced populations of sambar deer (Cervus unicolor) and rusa deer (Cervus timorensis) are present across south-eastern Australia and are subject to local population control to alleviate their negative impacts. For management to be effective, identification of dispersal capability and management units is necessary. These species also readily hybridise, so additional investigation of hybridisation rates across their distributions is necessary to understand the interactions between the two species.

Aim Measure the hybridisation rate of sambar and rusa deer, assess broad-scale population structure present within both species and identify distinct management units for future population control, and measure the likely dispersal capability of both species.

Methods In total, 198 sambar deer, 189 rusa deer, and three suspected hybrid samples were collected across Victoria and New South Wales (NSW). After sequencing and filtering, 14 099 polymorphic single-nucleotide polymorphism (SNP) markers were retained for analysis. Hybridisation rates were assessed before the data were split by species to identify population structure, diversity indices, and dispersal distances.

Key results Across the entire dataset, 17 hybrids were detected. Broad-scale population structure was evident in sambar deer, but not among the sites where rusa deer were sampled. Analysis of dispersal ability showed that a majority of deer movement occurred within 20 km in both species, suggesting limited dispersal.

Conclusions Distinct management units of sambar deer can be identified from the dataset, allowing independent population control. Although broad-scale population structure was not evident in the rusa deer populations, dispersal limits identified suggest that rusa deer sites sampled in this study could be managed separately. Sambar × rusa deer hybrids are present in both Victoria and NSW and can be difficult to detect on the basis of morphology alone.

Implications Genetic analysis can identify broad-scale management units necessary for population control, and estimates of dispersal capability can assist in delineating management units where broad-scale population structure may not be apparent. The negative impacts associated with hybridisation require further investigation to determine whether removal of hybrids should be considered a priority management aim.

Context Aerial shooting from a helicopter targeting introduced sambar deer (Cervus unicolor) is a key activity being undertaken on public land in the North East and East Gippsland regions of Victoria. However, there is currently little published information on the efficacy of aerial shooting for reducing sambar deer populations in Australia.

Aim The aims of this study were to analyse the operational data collected during an aerial shooting program in eastern Victoria, to assess the efficacy of aerial shooting at reducing sambar deer density and to inform management decisions on the required intensity of aerial shooting to achieve target densities.

Methods Operational data (locations of all shot animals as well as aerial search effort) were analysed from 10 sites using a Bayesian generalised catch–effort model, which allowed for population changes between five periods of intensive control. The model allowed estimates of initial and residual abundance for each site to be made from the catch–effort data, which were used to estimate the efficacy of aerial shooting. Estimates of the detection rate of deer, which were allowed to vary with removal occasion and site, were then used to estimate the amount of aerial search effort required to reduce population densities by various proportional amounts.

Key results Aerial shooting resulted in population reductions of 50–70% of sambar deer at four sites where aerial search intensities per unit area were highest. However, results at the remaining sites suggest that sambar deer densities have either remained static or increased over the five periods of aerial control. Recruitment of sambar deer between control periods, which was strongly influenced by study site elevation and season, was largely responsible for eroding reductions achieved by aerial shooting.

Conclusions Catch–effort models applied to operational data collected during aerial shooting programs can be used to estimate control efficacy without the need for additional monitoring. Our analysis suggests that sufficiently high search intensities, around 1.4 km of search effort per km² of habitat in each of five removal occasions, would need to be applied to achieve at least a 50% reduction in sambar deer densities.

Context There is concern about potential competition between non-native fallow deer (Dama dama) and livestock for food, particularly during times of low rainfall when pasture is scarce.

Aim We aimed to estimate the extent to which a high-density fallow deer population (~37 deer per km²) competed with livestock for food during a severe drought on pastoral properties on the Liverpool Plains, New South Wales, Australia.

Methods We collected rumen contents from 125 fallow deer shot from helicopters during control operations in June and August 2018, and used microhistology to quantify their diets. We then used the diet data to adjust published estimates of stock unit equivalence from farmed fallow deer. Fallow deer sex and age class abundances and stock unit equivalences were multiplied to estimate the grazing pressure of the fallow deer population pre- and post-control relative to recommended sheep and cattle stocking rates. Finally, we estimated density–impact relationships for fallow deer.

Key results Fallow deer diet was dominated by monocots (primarily grasses), but some individuals consumed large amounts of dicots (commonly Eucalyptus). Fallow deer were grazers to intermediate mixed feeders. Fallow deer dry-sheep equivalents (DSEs, based on a 50-kg merino wether) varied from 1.01 (juveniles) to 1.85 (adult females and adult males). Assuming complete diet overlap, the pre-control fallow deer population was equivalent to approximately 60.3 DSEs per km² and reduced the potential stocking rate of domestic livestock by 50.2%. Discounting the fallow deer DSEs by the amount of browse in the diet resulted in a pre-control population of 45.7 DSEs per km². The helicopter-based shooting reduced the fallow deer population by 26%, increasing the stocking rate in natural pasture by 22.0% (complete overlap) or 13.8% (discounting for browse).

Conclusions When food is limiting, fallow deer at high density can exert strong competitive pressure on livestock, reducing carrying capacity. Browsing, including on Eucalyptus, likely helped fallow deer to persist at high densities during the severe drought of 2018, when properties had destocked.

Implications Helicopter-based shooting reduced the competitive effects of fallow deer on livestock in our study area to only a small extent, but more intensive shooting would have led to a greater reduction. The helicopter-based shooting of deer was received positively by landholders at a time of severe stress, suggesting that deer control in agricultural areas can have other important benefits.

Context Some populations of introduced species cause significant undesirable impacts but can also act as reservoirs for genetic diversity. Sambar deer (Cervus unicolor) are ‘Vulnerable’ in their native range and invasive in Australia and New Zealand. Genetic data can be used to determine whether these introduced populations might serve as genetic reservoirs for declining native populations and to identify spatial units for management.

Aim We aimed to identify the provenance of sambar deer in Australia and New Zealand, and to characterise their genetic diversity and population structure.

Methods We used mitochondrial control region sequences and 18 nuclear microsatellite loci of 24 New Zealand and 63 Australian sambar deer collected across continuous habitat in each location. We estimated genetic diversity and population differentiation by using pairwise F_ST, AMOVA, and structure analyses. We compared our data with 27 previously published native and invasive range sequences to identify phylogenetic relationships.

Key results Sambar deer in Australia and New Zealand are genetically more similar to those in the west of the native range (South and Central Highlands of India, and Sri Lanka), than to those in the east (eastern India, and throughout Southeast Asia). Nuclear genetic diversity was lower than in the native range; only one mitochondrial haplotype was found in each introduced population. Australian and New Zealand sambar deer were genetically distinct but there was no population structure within either population.

Conclusions The genetic differences we identified between these two introduced populations at putatively neutral loci indicate that there also may be underlying diversity at functional loci. The lack of population genetic structure that we found within introduced populations suggests that individuals within these populations do not experience barriers to dispersal across the areas sampled.

Implications Although genetic diversity is reduced in the introduced range compared with the native range, sambar deer in Australia and New Zealand harbour unique genetic variants that could be used to strengthen genetic diversity in populations under threat in the native range. The apparent high levels of gene flow across the areas we sampled suggest that localised control is unlikely to be effective in Australia and New Zealand.

Context Chital deer (Axis axis) are long established in the northern Queensland dry tropics, and at high densities are considered pests by cattle graziers. Cost-effective management is difficult for widespread, fluctuating populations of vertebrate pests such as these deer. Historically, control of chital deer has been limited to recreational and some commercial ground-shooting and trapping. Concerns over chital deer impacts were heightened during drought in 2015 and funding became available for aerial culling.

Aim This study set out to determine (1) distribution and abundance, (2) seasonal reproductive output, (3) potential and actual rates of increase and their determinants, and (4) efficient management strategies for chital deer in the northern Queensland dry tropics.

Methods In 2014, ~13 000 km² of the main distribution was surveyed by helicopter. Multiple vehicle ground surveys per year monitored chital deer density on two properties during 2013–2022. Seasonal shot samples of deer on both properties assessed reproductive output during 2014–2016. Aerial surveys during 2016–2020 determined chital deer densities on seven properties, prior to aerial culling on four properties. Finally, the maximum rate of increase of chital deer was calculated from life-history data.

Key results Regionally, chital deer are patchily distributed and so are best monitored locally where densities can be >50 deer km⁻². Vehicle ground surveys recorded an ~80% decline in chital deer populations on two properties over 7–10 months during drought in early 2015, with a similar rate being recorded by aerial survey at a third site. There was little recruitment during the drought, but the decline was seemingly driven by adult mortality. Aerial shooting further reduced populations by 39–88% to <3 deer km⁻² on four properties. Where there was no continuing control, culled populations recovered to pre-cull densities or higher after 2.4 years. One unculled property recovered to its pre-drought density after 6 years. Rates of recovery were at or higher than the maximum annual rate of increase for chital deer estimated here as 26–41%.

Conclusions Drought has a lasting effect on this chital deer population, because of the resulting large population decline and the modest rate of any recovery in the absence of culling. Culling can reduce populations to low density, but the removal rate needs to be sustained to suppress future growth.

Implications Drought provides a strategic opportunity to further reduce chital deer populations for enduring control. Large reductions are feasible given the clumped dispersion of populations within properties and in the region.

Context A wild population of non-native hog deer has established in the Gippsland region of Victoria, Australia, and there is particular concern about its impact on native vegetation in Wilsons Promontory National Park (WPNP). Since 2015, there has been annual culling of hog deer at WPNP to reduce deer abundances and impacts.

Aim The aims of this study were to use a kinship approach based on genotyping to assess contemporary dispersal of hog deer across WPNP, by identifying close kin, to determine whether dispersal of deer into culled sites from unculled sites may affect the long-term success of management there. Differences in the dispersal of male and female hog deer were also investigated.

Methods In total, 91 hog deer tissue samples were collected across WPNP and surrounding sites. Single nucleotide polymorphism (SNP) markers were sequenced, and a final dataset comprising 8275 SNPs was used for analysis. First-order, second-order, and intermediate relative pairs were identified, and the geographic distance between these pairs was assessed to determine inter-pair distances to infer dispersal. Spatial autocorrelation between male and female samples was evaluated to measure the effects of sex-biased dispersal.

Key results Only seven second-order relative pairs were found across different sites, with a 30 km distance between the furthest pair observed. However, most inter-pair distances across sites were ~5–10 km. Analyses of sex-biased dispersal showed that movement by deer was not strongly influenced by one sex.

Conclusions Although hog deer in WPNP are genetically similar, most relatives that were sampled were not widely dispersed. This suggests that there is limited dispersal of hog deer across this park.

Implications Recolonisation of hog deer at culled sites via dispersal is likely to be infrequent in WPNP. Kinship analysis provides an effective method of assessing contemporary dispersal and could be applied to other species to assess fine-scale movement across landscapes.

Context Rusa deer (Cervus timorensis), originally introduced in the 1860s, are still spreading in eastern Australia. The expanding peri-urban rusa deer population in the Illawarra region of New South Wales, Australia is having undesirable impacts on human and ecological communities, but the spatial structure of this population has not been investigated. Genetic information on invasive species is potentially useful in identifying management units to mitigate undesirable impacts.

Aim The aim of this study was to investigate population structure, characterise dispersal, and determine if natural and human-made landscape features affected gene flow in rusa deer invading the Illawarra region of New South Wales.

Methods We used reduced representation sequencing (DArT-Seq) to analyse single nucleotide polymorphisms distributed throughout the genomic DNA of rusa deer culled during a management program. We used admixture and Principal Component Analyses to investigate population structure with respect to natural and human-made landscape features, and we investigated whether our genetic data supported the presence of sex-biased dispersal.

Key results Genetic diversity was highest in the north, near the original introduction site. A railway line demarcated restricted gene flow. Surprisingly, the Illawarra escarpment, a prominent landscape feature, did not restrict gene flow. There was no evidence of sex-biased dispersal and seven individuals were identified as genetic outliers.

Conclusions The genetic structure of the Illawarra rusa deer population is consistent with individuals spreading south from their introduction site in Royal National Park. The population is not panmictic, and a landscape feature associated with urbanisation was associated with increased spatial genetic structure. Outliers could indicate hybridisation or secondary incursion events.

Implications Rusa deer can be expected to continue invading southwards in the Illawarra region, but landscape features associated with urbanisation might reduce dispersal across the landscape. The genetic structuring of the population identified three potential management units on which to prioritise ground shooting operations.