Efficacy of the Boar-Operated-System to deliver baits to feral swine

Assessment of spilled toxic bait by wild pigs and potential risk to non-target species

BACKGROUND

In 2018, a sodium nitrite (SN)-based toxic bait for invasive wild pigs (hereafter wild pigs; Sus scrofa), was evaluated to determine its effectiveness in reducing local wild pig populations in Texas. Localized population reductions of >70% were achieved, but spillage of bait outside wild pig-specific feeders (bait stations) caused by feeding wild pigs resulted in the deaths of non-target animals. To evaluate risks to non-target animals, we tested whether bait presentation influenced the total amount of bait spilled by wild pigs and estimated the associated risk to non-target species.

RESULTS

We found that bait spilled outside bait stations could be reduced by >90% when compacted in trays, as opposed to being manually crumbled into pieces. We documented a mean spill rate of 0.913 g of bait per wild pig. Conservative risk assessments for nine non-target species for which SN toxicity data exist indicate that there is relatively low risk of lethal exposure, apart from zebra finches (Taeniopygia guttata) and white mice. Our results indicate that there may be enough spilled bait per feeding wild pig to kill 9.5 or 3.5 individuals of these species, respectively. Other species assessed range from 0.002 to 0.406 potential mortalities per wild pig.

CONCLUSION

We demonstrated that the amount of bait spilled by wild pigs during feeding and the associated risk to non-target animals can be minimized by presenting the bait compacted in trays within bait stations. We recommend that baits be tightly compacted and secured in bait stations to minimize risks to non-target animals from spilled bait by wild pigs. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Fertility Control for Wildlife: A European Perspective

Trends of human population growth and landscape development in Europe show that wildlife impacts are escalating. Lethal methods, traditionally employed to mitigate these impacts, are often ineffective, environmentally hazardous and face increasing public opposition. Fertility control is advocated as a humane tool to mitigate these impacts. This review describes mammalian and avian wildlife contraceptives' effect on reproduction of individuals and populations, delivery methods, potential costs and feasibility of using fertility control in European contexts. These contexts include small, isolated wildlife populations and situations in which lethal control is either illegal or socially unacceptable, such as urban settings, national parks and areas where rewilding occurs. The review highlights knowledge gaps, such as impact of fertility control on recruitment, social and spatial behaviour and on target and non-target species, provides a decision framework to assist decisions about the potential use of wildlife fertility control, and suggests eight reasons for Europe to invest in this area. Although developing and registering contraceptives in Europe will have substantial costs, these are relatively small when compared to wildlife's economic and environmental impact. Developing safe and effective contraceptives will be essential if European countries want to meet public demand for methods to promote human-wildlife coexistence.

Too many wild boar? Modelling fertility control and culling to reduce wild boar numbers in isolated populations

Wild boar and feral swine number and range are increasing worldwide in parallel with their impact on biodiversity and human activities. The ecological and economic impact of this species include spread of diseases, vehicle collisions, damage to crops, amenities and infrastructures and reduction in plant and animal abundance and richness. As traditional methods such as culling have not contained the growth and spread of wild boar and feral pigs, alternative methods such as fertility control are now advocated. We used empirical data on two isolated wild boar populations to model and compare the effects of different regimes of culling and fertility control on population trends. We built a Bayesian population model and applied it to explore the implications for population control of various management options combining culling and/or contraception. The results showed that, whilst fertility control on its own was not sufficient to achieve the target reduction in wild boar number, adding fertility control to culling was more effective than culling alone. In particular, using contraceptives on 40% of the population to complement the culling of 60% of the animals, halved the time to achieve our target reduction compared with culling only. We conclude that, assuming the effort of adding fertility control to culling was found to be cost-effective in terms of population reduction, these two methods should be used simultaneously if a rapid decrease in wild boar number is required for a closed population.

Fertility Control in Wildlife: Review of Current Status, Including Novel and Future Technologies

Wildlife conservation requires varying degrees of management of endangered species as well as management of their potential predators and competitors. Conservation also depends on ameliorating human-wildlife conflict, especially where there is a threat to the safety of people and of their pets and livestock. In addition, sustainability of wildlife populations can be affected by feral domestic animals or invasive species, that require removal or control. With the increasing concern for animal welfare, non-lethal methods of limiting population size and distribution, such as fertility control, are gaining favor. Breeding programs in zoos depend on highly effective and selective contraception to manage sustainable insurance populations. This review covers fertility control methods currently in use, those that have not lived up to past promises, and others that are under development and present hope for addressing remaining challenges.

Evaluation of movement behaviors to inform toxic baiting strategies for invasive wild pigs (Sus scrofa)

BACKGROUND

Invasive wild pigs damage agriculture, property, and natural ecosystems. To curtail damage, an effective and humane toxic bait containing microencapsulated sodium nitrite is under development. Strategies for delivering the toxic bait are needed to establish adequate spacing of bait sites, and for simultaneously accustoming wild pigs to the novel bait and wild pig-specific bait stations designed to exclude non-target species.

RESULTS

We monitored movements of 32 Global Positioning System (GPS)-collared wild pigs relative to 41 bait sites containing placebo bait. Among the bait sites, we compared three experimental baiting strategies (and a control) to evaluate which strategy led to the most wild pigs accessing the placebo bait inside bait stations. We found that bait sites should be spaced 0.5-1 km apart to maximize opportunities for all wild pigs to find and utilize the bait sites. Baiting strategies that allowed ≥ 15 days for accustoming wild pigs to bait stations were most effective and resulted in nearly 90% of wild pigs accessing the placebo bait inside the bait stations. Bait stations excluded all non-target animals, except one instance with a raccoon (Procyon lotor).

CONCLUSION

These results demonstrate the potential for toxic bait to be an effective tool for reducing populations of wild pigs with minimal risks to non-target species, if optimized delivery procedures are followed. © 2018 Society of Chemical Industry.

Contamination of wild boars' (Sus scrofa) muscles with tetracycline antibiotic from oral-delivered rabies vaccine baits

Tetracycline (TC) is used as a biomarker for rabies vaccine bait intended for foxes. However, there is a high probability of intake of the vaccine by other species living in the forest ecosystem, including wild boars (Sus scrofa), and TC residues can occur in the animals' tissues. In this study, muscle samples from 144 animals were tested for the presence of TC, collected after rabies vaccine distribution. For the quantitative analysis of TC and its 4-epi form, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed. The results of this study show that TC was found in 53 samples, which represents 37% of all tested animals. The concentrations were in the range 5-286 µg/kg. The preliminary results suggest that the risk exists of contamination of muscle tissue of wild boars with TC from oral-delivery rabies vaccine baits containing the antibiotic. Control should be considered of TC residues in wild boar meat for human consumption.

Seasonal variation in effectiveness of the boar-operated system to deliver baits to wild boar

BACKGROUND

Wild boar and feral pig numbers are growing worldwide and have substantial economic and environmental impacts. Bait-delivered pharmaceuticals such as disease vaccines, toxicants and contraceptives are advocated to mitigate these impacts. Effective campaigns based on these pharmaceuticals rely on optimising the target species' bait uptake, which may differ between seasons. We investigated seasonal differences in the use of Boar-Operated Systems (BOSs) by wild boar and non-target species in an English woodland.

RESULTS

In a pre-trial phase (BOS left open), wild boar, wild mammals, birds, livestock and companion animals fed on the peanuts and maize used as bait in the BOS. During the trial (BOS closed), only wild boar consumed the baits. Wild boar visited and fed from a larger number of BOSs in spring than in summer or winter. No aggressive intra-group interactions were recorded when wild boar fed from the BOSs but adult males were observed to monopolise two BOSs. Group size was highest in spring and bait uptake was lowest in winter.

CONCLUSION

The study confirmed the species-specificity of the BOS throughout the year and highlighted that, at least in this area, bait uptake by wild boar for baits delivered through the BOS would be maximised in spring. © 2017 Crown copyright. Pest Management Science © 2017 Society of Chemical Industry.

Bait Preference of Free-Ranging Feral Swine for Delivery of a Novel Toxicant

Invasive feral swine (Sus scrofa) cause extensive damage to agricultural and wildlife resources throughout the United States. Development of sodium nitrite as a new, orally delivered toxicant is underway to provide an additional tool to curtail growth and expansion of feral swine populations. A micro-encapsulation coating around sodium nitrite is used to minimize detection by feral swine and maximize stability for the reactive molecule. To maximize uptake of this toxicant by feral swine, development a bait matrix is needed to 1) protect the micro-encapsulation coating so that sodium nitrite remains undetectable to feral swine, 2) achieve a high degree of acceptance by feral swine, and 3) be minimally appealing to non-target species. With these purposes, a field evaluation at 88 sites in south-central Texas was conducted using remote cameras to evaluate preferences by feral swine for several oil-based bait matrices including uncolored peanut paste, black-colored peanut paste, and peanut-based slurry mixed onto whole-kernel corn. These placebo baits were compared to a reference food, whole-kernel corn, known to be readily taken by feral swine (i.e., control). The amount of bait consumed by feral swine was also estimated using remote cameras and grid boards at 5 additional sites. On initial exposure, feral swine showed reduced visitations to the uncolored peanut paste and peanut slurry treatments. This reduced visitation subsided by the end of the treatment period, suggesting that feral swine needed time to accept these bait types. The black-colored peanut paste was visited equally to the control throughout the study, and enough of this matrix was consumed to deliver lethal doses of micro-encapsulated sodium nitrite to most feral swine during 1–2 feeding events. None of the treatment matrices reduced visitations by nontarget species, but feral swine dominated visitations for all matrices. It was concluded that black-colored peanut paste achieved satisfactory preference and consumption by feral swine, and no discernable preference by non-target species, compared to the other treatments.

Fertility control to mitigate human–wildlife conflicts: a review

As human populations grow, conflicts with wildlife increase. Concurrently, concerns about the welfare, safety and environmental impacts of conventional lethal methods of wildlife management restrict the options available for conflict mitigation. In parallel, there is increasing interest in using fertility control to manage wildlife. The present review aimed at analysing trends in research on fertility control for wildlife, illustrating developments in fertility-control technologies and delivery methods of fertility-control agents, summarising the conclusions of empirical and theoretical studies of fertility control applied at the population level and offering criteria to guide decisions regarding the suitability of fertility control to mitigate human–wildlife conflicts. The review highlighted a growing interest in fertility control for wildlife, underpinned by increasing numbers of scientific studies. Most current practical applications of fertility control for wild mammals use injectable single-dose immunocontraceptive vaccines mainly aimed at sterilising females, although many of these vaccines are not yet commercially available. One oral avian contraceptive, nicarbazin, is commercially available in some countries. Potential new methods of remote contraceptive delivery include bacterial ghosts, virus-like particles and genetically modified transmissible and non-transmissible organisms, although none of these have yet progressed to field testing. In parallel, new species-specific delivery systems have been developed. The results of population-level studies of fertility control indicated that this approach may increase survival and affect social and spatial behaviour of treated animals, although the effects are species- and context-specific. The present studies suggested that a substantial initial effort is generally required to reduce population growth if fertility control is the sole wildlife management method. However, several empirical and field studies have demonstrated that fertility control, particularly of isolated populations, can be successfully used to limit population growth and reduce human–wildlife conflicts. In parallel, there is growing recognition of the possible synergy between fertility control and disease vaccination to optimise the maintenance of herd immunity in the management of wildlife diseases. The review provides a decision tree that can be used to determine whether fertility control should be employed to resolve specific human–wildlife conflicts. These criteria encompass public consultation, considerations about animal welfare and feasibility, evaluation of population responses, costs and sustainability.

Effects of a GnRH vaccine on the movement and activity of free-living wild boar (Sus scrofa)

Context Fertility control is being promoted as a non-lethal means of managing wildlife populations. We recently evaluated a single-dose injectable immunocontraceptive vaccine (GonaCon™) on captive female wild boar for effectiveness and potential side effects; reproductive output was inhibited for 4–6 years, with no obvious detrimental effects on physiology and behaviour. Aims We injected individual free-living wild boar individuals with the fertility-control vaccine GonaCon™ to examine its effectiveness (measured as raised levels of GnRH antibodies) and looked for potential changes in movement and activity patterns. Methods We trapped, fitted telemetry devices to, and released wild boar individuals living in woodland in the West Midlands region of England between 2006 and 2010. We compared data on movements and activity among 10 adult females treated with the vaccine and 11 controls treated with saline only. We measured anti-GnRH antibody titres in six recaptured boar individuals as an indicator of the effectiveness of the vaccine. Key results Post-treatment GnRH antibody titres varied among the boar individuals; four of five treated sows resampled between 9 and 30 weeks post-injection had antibody titres high enough to block reproduction (detectable at 1 : 32 000–1 : 64 000 dilution). At least three treated females were pregnant at the time of vaccination; there was no subsequent evidence that the vaccine interfered with pregnancy. According to the distances moved per hour over a 24-h cycle and the daily activity cycle in relation to season, there were no differences in the behaviour of treated and control females that were likely to be biologically significant. The behaviour of two treated females monitored soon after vaccination and again 12 months later also showed no major differences. Conclusions Free-living wild boar responded to treatment with a 1.0-mL (1000 µg) dose of an anti-GnRH vaccine and no major adverse effects on activity and movement were subsequently detected. Implications Our results indicated that the vaccine could be more widely evaluated in the field against overabundant or nuisance populations. Such populations are increasingly found in urban areas and parks, where culling may not be an option. We suggest that further refinement of this approach for managing wild boar populations, including development of an oral vaccine, are warranted.

Monitoring wild pig populations: a review of methods

Wild pigs (Sus scrofa) are widespread across many landscapes throughout the world and are considered to be an invasive pest to agriculture and the environment, or conversely a native or desired game species and resource for hunting. Wild pig population monitoring is often required for a variety of management or research objectives, and many methods and analyses for monitoring abundance are available. Here, we describe monitoring methods that have proven or potential applications to wild pig management. We describe the advantages and disadvantages of methods so that potential users can efficiently consider and identify the option(s) best suited to their combination of objectives, circumstances, and resources. This paper offers guidance to wildlife managers, researchers, and stakeholders considering population monitoring of wild pigs and will help ensure that they can fulfill their monitoring objectives while optimizing their use of resources.

Progress in Oral Vaccination against Tuberculosis in Its Main Wildlife Reservoir in Iberia, the Eurasian Wild Boar

Eurasian wild boar (Sus scrofa) is the main wildlife reservoir for tuberculosis (TB) in Iberia. This review summarizes the current knowledge on wild boar vaccination including aspects of bait design, delivery and field deployment success; wild boar response to vaccination with Bacillus Calmette-Guérin (BCG) and inactivated Mycobacterium bovis; and wild boar vaccination biosafety issues as well as prospects on future research. Oral vaccination with BCG in captive wild boar has shown to be safe with significant levels of protection against challenge with virulent M. bovis. An oral vaccination with a new heat-killed M. bovis vaccine conferred a protection similar to BCG. The study of host-pathogen interactions identified biomarkers of resistance/susceptibility to tuberculosis in wild boar such as complement component 3 (C3) and methylmalonyl coenzyme A mutase (MUT) that were used for vaccine development. Finally, specific delivery systems were developed for bait-containing vaccines to target different age groups. Ongoing research includes laboratory experiments combining live and heat-killed vaccines and the first field trial for TB control in wild boar.

Effects of culling Eurasian wild boar on the prevalence of Mycobacterium bovis and Aujeszky's disease virus

Worldwide, failure to eradicate a disease in livestock has sometimes been related to wildlife reservoirs of infection. We describe the effects of Eurasian wild boar (Sus scrofa) abundance reduction through increased culling on the prevalence of two chronic infectious diseases, tuberculosis (TB) and Aujeszky's disease (AD), in a region of South-central Spain (SCS). The two infections studied responded differently to an approximately 50% reduction of wild boar abundance. Wild boar TB prevalence remained stable in control sites, whereas it decreased by 21-48% in treatment sites. In one treatment site, the annual wild boar abundance was positively correlated with the annual percentage of skin test reactor cattle. In another treatment site, red deer (Cervus elaphus) M. bovis infection prevalence decreased after culling wild boar. No significant effect of wild boar culling on wild boar ADV seroprevalence was found. The reduction in wild boar TB was achieved despite no alternative M. bovis host being included in the culling strategy. We advocate that culling could become a part of integrated control strategies including habitat and game management changes and vaccination, contributing to increase their success likelihood, or reducing the total expenses.