Strength testing of raccoons and invasive wild pigs for a species‐specific bait station

Abstract

With the development of a toxic bait (HOGGONE®) for the control of invasive wild pig (IWP; Sus scrofa) populations in the United States, there is a need to develop a bait station to mitigate potential effects on nontarget species. Our objective was to identify characteristics of a bait station that can successfully exclude raccoons (Procyon lotor)—a ubiquitous and dexterous nontarget species—while facilitating bait consumption by IWPs that exhibit group‐feeding behaviors. We evaluated abilities of captive raccoons (n = 19) and IWPs (n = 41) to open the lids of prototype resistance assessment bait stations (RABS) under various levels of resistance (range = 1.1–18.1 kg) at research facilities in Colorado and Texas, USA, during July–August 2014. We found that similar proportions (0.65) of individual raccoons and IWPs in our tests opened lids with 0–1.4 kg resistance, which decreased as resistance increased. No raccoons opened lids with ≥13.6 kg of resistance. However, equal proportions (0.45) of IWPs opened lids with 13.6 kg and 18.1 kg, and a greater proportion (0.73) secondarily accessed RABS after other IWPs opened them. Scrounging behaviors of IWPs (i.e., aggressively taking access to food from less dominate IWPs) increased as the levels of resistance increased, but similar proportions of animals gained access. These results suggest that a threshold‐weight‐of‐resistance of 13.6–18.1 kg on hinged lids excludes raccoons and allows access by IWPs. Furthermore, bait stations designed to allow multiple IWPs to feed simultaneously may be preferred because of group feeding behaviors. Field evaluations are required to evaluate the exclusion of other nontarget species (e.g., white‐tailed deer [Odocoileus virginianus], black bears [Ursus americanus], and coyotes [Canis latrans]), potential scrounging behaviors by nontargets, and bait consumption by IWPs. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

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

“…Therefore, it is unclear whether the raccoon gained access because it learned to overcome the magnetic resistance, or perhaps the wild pigs dropped some debris on the magnets, causing the magnets to malfunction. Based on previous results suggesting that raccoons are incapable of breaking 13 kg of magnetic resistance, we suspect the latter.…”

“…Additionally, from stage 4 onwards, we applied 16 g of peanut butter to the underside of bait station lids to entice wild pigs to explore under the lid during the following stages. At the initiation of stage 5, we installed magnets paired with steel strike plates into the junction of lids and bait station frames requiring wild pigs to exceed ∼ 13.6 kg of resistance to access and consume bait from inside the bait stations . All strategies eventually ended with stage 6, two simulated toxic days with 20 kg of placebo bait.…”

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

“…Another important consideration for using SN toxic baits in the field is the risk to non‐target wildlife. Risks of secondary poisoning for scavengers of wild pig carcasses were reportedly low, risks of non‐targets directly accessing bait in the bait stations were similarly low, but the risk of non‐targets accessing bait dropped by wild pigs outside bait stations is currently unknown. Notably, upon morning inspections, we observed almost undetectable amounts of biomarker bait left outside the bait stations by wild pigs.…”

“…On day 8, we deployed wild pig‐specific bait stations at all 30 of the baiting sites. Each bait station (137 cm length × 36 cm width × 17 cm height) consisted of two back‐to‐back troughs with overhanging lids that could be positioned from propped completely open to secured closed with 13 kg of magnetic resistance . We secured bait stations to the ground by wiring the handles to two T‐posts to prevent flipping or removal by wild pigs.…”

“…Initial studies with SN toxic bait have demonstrated a high level of palatability and efficacy for wild pigs, and low secondary risks to non‐target scavenger species . A wild pig‐specific bait station has also been developed that successfully excludes non‐target species, including the capable and ubiquitous raccoon ( Procyon lotor ), preventing non‐target species from directly accessing the toxic bait inside the bait stations while still allowing access by wild pigs . Usage of the bait station by wild pigs, however, required a 2–3‐week pre‐baiting period for pigs to become accustomed to the bait station .…”