Brendan D. Cowled

Efficacy of manufactured PIGOUT® baits for localised control of feral pigs in the semi-arid Queensland rangelands

Conservative population declines of 73% were recorded in three independent feral pig populations in Welford National Park, Queensland, when PIGOUT® baits containing 72 mg of sodium fluoroacetate were used in a baiting program following prefeeding. Declines were measured using a prebaiting population census with remote cameras, followed by carcass recovery. The knockdown of susceptible feral pigs may have been higher than this, since any carcasses not recovered reduced the recorded efficacy. In addition, feral pigs know to have left the baiting area after trapping and telemetry-tagging, and subsequently not exposed to toxic baits, were included in the analysis. The use of remote cameras and carcass recovery appears to be a relatively accurate means of recording localised declines in feral pig populations. This method is applicable only when carcass recovery is possible, such as in open areas in the semi-arid rangelands. A decline of 86% of radio-tagged feral pigs attending bait stations was also recorded. Camera observations revealed no non-target consumption of baits. Measurement of sodium fluoroacetate–contaminated tissues from feral pigs showed that residues were too low to present a significant risk to recorded scavenging animals in the area. Some feral pigs vomited before death, with vomitus containing sodium fluoroacetate poison at high concentrations. No vomitus was consumed by non-target species. Almost all feral pigs were killed relatively rapidly after ingestion of sodium fluoroacetate and the signs observed in a small number of poisoned feral pigs did not indicate a significant welfare concern.

Attractiveness of a novel omnivore bait, PIGOUT®, to feral pigs (Sus scrofa) and assessment of risks of bait uptake by non-target species

Following a bait-preference pilot study on captive feral pigs, a series of field studies assessed the attractiveness and target-specificity of a prototype manufactured feral pig bait (PIGOUT®). Two promising test baits and fresh meat reference baits were biomarked with iophenoxic acid and aerially distributed in 100-km2 blocks of land infested with feral pigs in western Queensland to assess field uptake and target-specificity without prefeeding. Uptake was assessed by measuring blood iodine levels in aerially shot feral pigs. In all, 80% of feral pigs sampled in a non-toxic PIGOUT®-baited area had significantly elevated blood iodine, compared with 52% of sampled feral pigs in a meat-baited area (although slightly different baiting strategies were employed). No age or sex bias was evident in PIGOUT®-consuming feral pigs. No monitored manufactured baits were consumed by non-target species in 500 bait-nights. Attractiveness and target-specificity trials of ground-laid, unfenced PIGOUT® baits compared with reference baits were subsequently undertaken in several regions of eastern Australia. Results showed that PIGOUT® was consumed readily by feral pigs at all sites, and that it offered significant improvement in target specificity when compared with unfenced wheat or meat baits. However, the baits were consumed by small numbers of macropods, birds and possums. Available evidence indicates that the target-specificity of PIGOUT® bait is highest in the rangelands, reducing slightly in temperate areas and subalpine forests, where abundance of small animals is higher.

Measuring the Demographic and Genetic Effects of Pest Control in a Highly Persecuted Feral Pig Population

Abstract Substantial efforts have been made to identify the most effective practices for the control and management of invasive vertebrate pest species, such as the feral pig (Sus scrofa). We investigated the demographics, abundance, and molecular ecology of a persecuted feral pig population that was subjected to control. We then applied methodologies to determine if we could retrospectively quantify any changes in the population structure or dynamics of these pigs. Feral pig demographic and abundance parameters indicated that in this population of feral pigs, there were very few detectable changes between the two aerial culling years. We observed this despite environmental conditions being optimal for control. Genetic results indicated that pigs culled in the latter 2004 cull were genetically identical to those pigs that inhabited the area a year earlier. The genetic population was geographically larger than the sample area. These findings indicate that the recovery in feral pig density witnessed in the controlled area was not a result of reinvasion from a separate, genetically distinct population, but rather, it was the result of reinvasion from feral pigs outside the study area but within the same genetic population. Importantly, we were unable to detect any recent genetic bottlenecks. This approach has considerable potential for auditing the effectiveness of control programs of pest species and assessing the feasibility of impacting upon or locally eradicating many other free-ranging pest species.

Feral pigs: predicting future distributions

Feral pig populations are expanding in many regions of the world following historically recent introductions. Populations are controlled to reduce damage to agriculture and the environment, and are also a recreational hunting resource. Knowledge of the area over which feral pigs may expand in the future could be used regionally to assist biosecurity planning, control efforts and the protection of biodiversity assets. The present study sought to estimate the future distribution of a recently introduced, expanding feral pig population in the remote Kimberley region of north-western Australia. An existing survey of feral pig distributions was enhanced and remote-sensing and weather data, reflecting or correlated with factors that may affect feral pig distributions, were collated and analysed. Relationships between feral pig distributions and these data were identified by using a generalised additive modelling approach. By the use of the model, the distribution of favourable habitat was estimated across the study region (89 125 km2). The potential future distribution of feral pigs in the Kimberley was then estimated, assuming only natural dispersal of feral pigs from areas of known feral pig status (cf. hunter-assisted movements or escape of domestic pigs). The modelling suggests that feral pigs could expand their distribution by realistic natural dispersal in the future (to 61 950 km2). This expansion possibility contains several strategically important areas (such as sea ports and biologically significant wetlands). This approach has the potential to improve biosecurity planning for the containment of the feral pig in the Kimberley and may have utility for other recently introduced invasive species in other regions. These results may also be used to improve pest-management programmes and contingency planning for exotic-disease incursions.

Vaccination of feral pigs (Sus scrofa) using iophenoxic acid as a simulated vaccine

OBJECTIVES To develop an encapsulation method for delivery of vaccines to feral pigs, and quantify the effect of iophenoxic acid on captive feral pig blood iodine concentrations to assist in investigation of factors affecting vaccine uptake. DESIGN AND METHODS Feral pigs were administered iophenoxic acid by oral gavage, and consumption was assessed for different encapsulation methods in baits. Blood iodine concentrations were monitored for eight days after consumption. The relationship between dose rate, time since dosing and blood iodine concentration was assessed for gavaged and baited captive feral pigs. Wild feral pigs were baited with PIGOUT baits containing 20 mg of encapsulated iophenoxic acid to simulate a vaccination program. Using knowledge from the pen studies, bait uptake and factors affecting bait uptake were investigated. RESULTS Bait-delivered iophenoxic acid led to variable and inconsistent changes in blood iodine concentrations, in contrast to pigs receiving iophenoxic acid by gavage. This precluded accurate assessment of the quantity consumed, but still allowed a conservative determination of bait uptake. Iophenoxic acid in smaller capsules was consumed readily. Increasing baiting intensity appeared to increase bait uptake by wild feral pigs, and pigs of varying sexes, ages and weights appeared equally likely to consume baits. CONCLUSIONS Encapsulated liquids can be delivered to feral pigs within baits, should the need to vaccinate feral pigs for fertility or disease management arise. High baiting intensities may be required.

Quantitative analysis of animal-welfare outcomes in helicopter shooting: a case study with feral dromedary camels (Camelus dromedarius)

Abstract Context. Helicopter shooting is a common and effective tool for reducing overabundant wildlife populations. However, there is little quantitative information on the humaneness of the method, leading to uncertainty in wildlife-management policy. There is, subsequently, a need for an improved understanding of the welfare implications of helicopter shooting. Aim. A study was undertaken to infer the humaneness of helicopter shooting for a case study species, the feral dromedary camel (Camelus dromedarius). Methods. Seven post-mortem studies (n = 715) and one ante-mortem study (n = 192) were undertaken during routine helicopter shooting programs of free-ranging camels. In these studies, we measured four animal-welfare parameters to allow inference on the humaneness of the technique. These parameters were time to death, instantaneous death rate (proportion of animals for which time to death = 0), wounding rate and location of bullet-wound tract. We also modelled these welfare variables against hypothesised explanatory variables to assist improvement of future programs. Key results. The mean wounding rate was 0.4%, and the killing efficacy of the technique was 99.6%. Mean time to death was 4 s, and mean instantaneous death rate was 83%. Each animal displayed a mean 2.4 bullet-wound tracts, with 75%, 63% and 35% of animals shot at least once in the thorax, cranium and cervical spine, respectively. Regression analysis revealed that the identity of the shooter and the nature of the local vegetation were the most important factors associated with an animal experiencing an inferred instantaneous death or not. Conclusions. Helicopter shooting of feral camels produces a very low wounding rate and rapid time to death. Shooter identity is the most important consideration for determining animal-welfare outcomes. Improvements to the humaneness of programs can be made by increasing the rigour of shooter selection and training. Implications. Wildlife killing methods must be demonstrated to be humane to receive public support; however, few shooting methods are objectively examined. Helicopter shooting can be independently examined and operators assessed. Adoption of this examination template may allow continual improvement by industry as well as increasing societal acceptance of helicopter shooting.

Assessment of animal welfare for helicopter shooting of feral horses

Abstract Context. Helicopter shooting is an effective tool for reducing feral horse (Equus caballus) populations that are considered overabundant. However, this tool has been less commonly used in recent years because of concerns about animal-welfare outcomes, which have not previously been quantified. Aims. The aims of the present study were to assess the helicopter shooting of feral horses to determine (1) the duration of stress, (2) the frequency of adverse animal-welfare events and (3) the influence of explanatory variables in determining welfare outcomes. Methods. We quantified the welfare outcomes of three helicopter shooting programs in central Australia during 2013 and 2015. We conducted ante-mortem observations of 937 horses and post-mortem observations of 630 horses. We measured the following three parameters to estimate the duration of stress from pursuit and the mode of death: chase time (CT), time to death (TTD) and total time (TT; CT+TTD). We quantified the frequency of adverse animal-welfare events, namely instantaneous death rate (IDR; percentage of animals for which TTD was zero), the apparent frequency of non-fatal wounding, and the frequency of bullet-wound tracts in different anatomical locations. We investigated the role of explanatory variables in determining whether or not a horse had an inferred instantaneous death. Key results. For all horses, the median CT was 42 s, the median TTD was 0 s (median TTD for horses not killed instantaneously was 15 s), and median TT was 52 s. At least 1% of horses were non-fatally wounded, IDR was 63% (60–66%), and 3% (2–5%) of horses were not shot in the cranium, neck or thorax. Shooter skill was the most important determinant of whether or not a horse had an instantaneous death. Conclusions. The animal-welfare outcomes of helicopter shooting appear to be similar for feral horses and feral camels (Camelus dromedarius), the only other species that has been studied using these methods, and could be refined by improving shooter skill. Implications. Quantifying animal-welfare outcomes is particularly important for contentious wildlife management techniques. Wildlife managers should integrate the results of welfare studies into decision-making processes rather than excluding contentious techniques from consideration on the basis of perception.