Potential secondary poisoning risks to non-targets from a sodium nitrite toxic bait for invasive wild pigs

Comparing efficiencies of population control methods for responding to introductions of transboundary animal diseases in wild pigs

Introductions of transboundary animal diseases (TADs) into free-ranging wildlife can be difficult to control and devastating for domestic livestock trade. Combating a new TAD introduction in wildlife with an emergency response requires quickly limiting spread of the disease by intensely removing wild animals within a contiguous area. In the case of African swine fever virus (ASFv) in wild pigs (Sus scrofa), which has been spreading in many regions of the world, there is little information on the time- and cost-efficiency of methods for intensively and consistently culling wild pigs and recovering carcasses in an emergency response scenario. We compared the efficiencies of aerial operations, trapping, experimental toxic baiting, and ground shooting in northcentral Texas, USA during two months in 2023. Culling and recovering carcasses of wild pigs averaged a rate of 0.15 wild pigs/person hour and cost an average of $233.04/wild pig ($USD 2023) across all four methods. Aerial operations required the greatest initial investment but subsequently was the most time- and cost-efficient, costing an average of $7266 to reduce the population by a standard measure of 10 %, including recovering carcasses. Aerial operations required a ground crew of ∼7 people/helicopter to recover carcasses. Costs for reducing the population of wild pigs using trapping were similar, although took 13.5 times longer to accomplish. In cases where carcass recovery and disposal are needed (e.g., response to ASFv), a benefit of trapping was immediate carcass recovery. Toxic baiting was less efficient because both culling and carcass recovery required substantial time. We culled very few wild pigs with ground shooting in this landscape. Our results provide insight on the efficiencies of each removal method. Strategically combining removal methods may increase overall efficiency. Overall, our findings inform the preparation of resources, personnel needs, and deployment readiness for TAD responses involving wild pigs.

Seasonal efficacy and risks from a sodium nitrite toxic bait for wild pigs

BACKGROUND

Wild pigs (Sus scrofa) are an invasive and destructive species throughout many regions of the world. A sodium nitrite (SN) toxic bait is currently used in Australia and being developed for use in the US and other countries to combat the increasing populations of wild pigs. In the US, efforts to modify the Australian SN-toxic bait and baiting strategy have focused on reducing issues with non-target animals accessing the SN-toxic bait spilled outside of bait stations by wild pigs. We tested and compared modifications for efficacy (with wild pigs) and hazards (with non-targets) in north-central Texas, US during summer (July 2021) and winter (March 2023) seasons.

RESULTS

During both seasons we found that visitation to the bait sites declined 94-99% after deploying the SN-toxic bait, and we found a total of 106 dead wild pigs, indicating considerable lethality for the local population. Prior to deploying the SN-toxic bait, Global Positioning System (GPS)-collared wild pigs were more likely to cease visiting bait sites during summer when foraging resources were abundant. Farrowing decreased visitation to bait sites during the winter. We observed no dead non-targets during summer; winter results showed an average of 5.2 dead migrating birds per bait site (primarily Dark-eye juncos [Junco hyemalis]) from consuming SN-toxic bait spilled by wild pigs. The presence and winter-foraging behaviors of migrating birds appeared to increase hazards for those species.

CONCLUSION

The current formulation of SN-toxic bait was effective at removing wild pigs during both seasons, however it is clear that different baiting strategies may be required in winter when migrating birds are present. Baiting wild pigs prior to farrowing during the winter, and during drier summers, may further improve efficacy of the bait. Reducing hazards to non-targets could be achieved by refining the SN-toxic bait or modifying bait stations to decrease the potential for spillage, decreasing environmental persistence if spilled, or decreasing attractiveness to migrating birds. © 2024 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.

Integrating terrestrial scavenging ecology into contemporary wildlife conservation and management

Scavenging plays a vital role in maintaining ecosystem health and contributing to ecological functions; however, research in this sub-discipline of ecology is underutilized in developing and implementing wildlife conservation and management strategies. We provide an examination of the literature and recommend priorities for research where improved understanding of scavenging dynamics can facilitate the development and refinement of applied wildlife conservation and management strategies. Due to the application of scavenging research broadly within ecology, scavenging studies should be implemented for informing management decisions. In particular, a more direct link should be established between scavenging dynamics and applied management programs related to informing pharmaceutical delivery and population control through bait uptake for scavenging species, prevention of unintentional poisoning of nontarget scavenging species, the epidemiological role that scavenging species play in disease dynamics, estimating wildlife mortalities, nutrient transfer facilitated by scavenging activity, and conservation of imperiled facultative scavenging species. This commentary is intended to provide information on the paucity of data in scavenging research and present recommendations for further studies that can inform decisions in wildlife conservation and management. Additionally, we provide a framework for decision-making when determining how to apply scavenging ecology research for management practices and policies. Due to the implications that scavenging species have on ecosystem health, and their overall global decline as a result of anthropic activities, it is imperative to advance studies in the field of scavenging ecology that can inform applied conservation and management programs.

Deterring non-target birds from toxic bait sites for wild pigs

Toxic baiting of wild pigs (Sus scrofa) is a potential new tool for population control and damage reduction in the US. Field trials testing a prototype toxic bait (HOGGONE 2 containing 5% sodium nitrite [SN]), though, revealed that wild pigs spilled small particles of toxic bait outside of bait stations which subsequently created hazards for non-target species that consumed those particles, primarily passerine birds. To deter non-target birds from consuming particles of spilled bait, we tested four deterrents at mock bait sites (i.e., baited with bird seed) in north-central Colorado, USA during April–May 2020. We found a programable, inflatable deterrent device (scare dancer) reduced bird visitation by an average of 96%. Then, we evaluated the deterrent devices at SN-toxic bait sites in north-central Texas, USA during July 2020, where the devices were activated the morning following deployment of SN-toxic bait. Overall, we found 139 dead wild pigs at 10 bait sites following one night of toxic baiting, which represented an average of 91% reduction in wild pigs visiting bait sites. We found that deterrent devices were 100% effective at deterring birds from toxic bait sites. We found two dead non-target mice at bait sites without deterrent devices. We noted that deploying toxic bait in mid-summer rather than late-winter/early-spring reduced hazards to migrating birds because they were not present in our study area during July. We recommend using deterrent devices (i.e., novel, programmable, battery operated, continuous and erratic movement, and snapping sounds) to reduce hazards to non-target birds at SN-toxic bait sites. We further recommend deploying SN-toxic bait during seasons when migrating birds are not as abundant until further research demonstrates minimal risks to migrating birds.

Efficacy and risks from a modified sodium nitrite toxic bait for wild pigs

BACKGROUND

Wild pigs (Sus scrofa) are a destructive invasive species throughout many regions of the world. In 2018, a field evaluation of an early prototype of a sodium nitrite (SN) toxic bait in the United States revealed wild pigs dropped large amounts of the toxic bait outside the pig-specific bait stations while feeding, and thus subsequent hazards for non-target animals. We modified the SN-toxic bait formulation, the design of the bait station, and the baiting strategy to reduce dropped bait. We tested the modifications in Queensland, Australia (December 2018), Alabama, USA (August 2019), and Texas, USA (March 2020) under differing climatic and seasonal conditions for one night.

RESULTS

Cumulatively we found 161 carcasses of all age classes of wild pigs using systematic transects. Remote camera indices indicated high lethality for wild pigs, achieving population reductions of 76.3 to 90.4%. Wild pigs dropped only small particles of SN-toxic bait (average = 55.5 g per bait site), which represented a 19-fold decrease from the previous trial. Despite this reduction, we found three Australian ravens (Corvus coronoides) in Queensland, two Virginia opossums (Didelphis virginiana) in Alabama, and 35 granivorous-passerine birds (mostly dark-eyed juncos [Junco hyemalis]) in Texas dead from consuming the dropped bait. We did not detect any population-level effects for those species.

CONCLUSION

Our modifications were effective at reducing populations of wild pigs, but the deaths of non-target species require further steps to minimize these hazards. Next steps will include evaluating various deterrent devices for birds the morning after SN-toxic bait has been offered. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Toxicity of sodium nitrite-based vertebrate pesticides for European starlings (Sturnus vulgaris)

In the 21st century, invasive animals rank second only to habitat destruction as the greatest threat to global biodiversity. Socially-acceptable and cost-effective strategies are needed to reduce the negative economic and environmental impacts of invasive animals. We investigated the potential for sodium nitrite (SN; CAS 7632-00-0) to serve as an avian toxicant for European starlings (Sturnus vulgaris L.). We also assessed the non-target hazard of an experimental formulation of SN that is being developed as a toxicant for invasive wild pigs (Sus scrofa L.). In gavage experiments with European starlings, we identified a lowest observed adverse effect level (LOAEL) for mortality of 2.40% technical SN (w/v; 120 mg SN/kg body mass) and a no observed adverse effect level (NOAEL) for mortality of 1.30% technical SN (65 mg/kg). The exposure of ten starlings to the experimental formulation of SN (10% SN pig toxicant) resulted in one starling mortality during four days of exposure to the toxic bait. Sodium nitrite toxicity presented a moderate hazard to European starlings; thus, the future development of SN as an avian toxicant is dependent upon its cost-effectiveness. We discuss the management of toxic effects and non-target hazards of SN for wild birds, including best practices for toxic baiting of vertebrate pests and management of invasive wild pigs.

Technology innovation: advancing capacities for the early detection of and rapid response to invasive species

The 2016–2018National Invasive Species Council (NISC) Management Plan and Executive Order 13751 call for US federal agencies to foster technology development and application to address invasive species and their impacts. This paper complements and draws on an Innovation Summit, review of advanced biotechnologies applicable to invasive species management, and a survey of federal agencies that respond to these high-level directives. We provide an assessment of federal government capacities for the early detection of and rapid response to invasive species (EDRR) through advances in technology application; examples of emerging technologies for the detection, identification, reporting, and response to invasive species; and guidance for fostering further advancements in applicable technologies. Throughout the paper, we provide examples of how federal agencies are applying technologies to improve programmatic effectiveness and cost-efficiencies. We also highlight the outstanding technology-related needs identified by federal agencies to overcome barriers to enacting EDRR. Examples include improvements in research facility infrastructure, data mobilization across a wide range of invasive species parameters (from genetic to landscape scales), promotion of and support for filling key gaps in technological capacity (e.g., portable, field-ready devices with automated capacities), and greater investments in technology prizes and challenge competitions.

Exposure of a population of invasive wild pigs to simulated toxic bait containing biomarker: implications for population reduction

BACKGROUND

An international effort to develop an acute and humane toxic bait for invasive wild pigs (Sus scrofa) is underway to curtail their expansion. We evaluated the ability to expose a population of wild pigs to a simulated toxic bait (i.e., placebo bait containing a biomarker, rhodamine B, in lieu of the toxic ingredient) to gain insight on potential population reduction. We used 28 GPS-collars and sampled 428 wild pigs to examine their vibrissae for evidence of consuming the bait.

RESULTS

We estimated that 91% of wild pigs within 0.75 km of bait sites (total area = 16.8 km² ) consumed the simulated toxic bait, exposing them to possible lethal effects. Bait sites spaced 0.75-1.5 km apart achieved optimal delivery of the bait, but wild pigs ranging ≥ 3 km away were susceptible. Use of wild pig-specific bait stations resulted in no non-target species directly accessing the bait.

CONCLUSION

Results demonstrate the potential for exposing a large proportion of wild pigs to a toxic bait in similar ecosystems. Toxic baits may be an effective tool for reducing wild pig populations especially if used as part of an integrated pest management strategy. Investigation of risks associated with a field-deployment of the toxic bait is needed. © 2018 Society of Chemical Industry.