Low secondary risks for captive coyotes from a sodium nitrite toxic bait for invasive wild pigs.
An acute toxic bait is being developed to deliver micro-encapsulated sodium nitrite (SN) to stimulate severe methemoglobinemia and humane death for invasive wild pigs (Sus scrofa), thereby providing a new tool for reducing their populations. During April 2016, we evaluated sensitivity to SN and outcomes of secondary consumption in the ubiquitous mammalian scavenger, coyote (Canis latrans), to determine secondary risks of consuming carcasses of wild pigs that died from consuming the SN toxic bait. At the National Wildlife Research Center in Fort Collins, Colorado, USA, we first evaluated whether coyotes fed carcasses of domestic pigs killed by consumption of SN bait showed signs of SN intoxication. Second, we conducted chemical analysis of residual SN in the coyotes for evidence of SN passing from pigs to coyotes. Last, we conducted an acute oral toxicity test (LD50) with SN for coyotes by feeding them meatballs containing capsules of SN. We found no evidence that captive coyotes experienced SN intoxication from consuming on carcasses that had been freshly poisoned with SN, despite consuming x¯=1.6 kg of tissues/coyote within 24 hours. None of the captive coyotes consumed digestive tracts or stomach contents from poisoned carcasses, which contained the highest levels of residual SN. Chemical analysis indicated that only ≤34.14 mg/kg of residual SN were passed from the tissues of the pigs into the coyotes, confirming that SN does not bioaccumulate. All coyotes quickly vomited various doses of SN during the LD50 test and fully recovered, suggesting a natural defense against secondary poisoning from SN. Testing with captive coyotes indicates that the risks of secondary poisoning for free-ranging coyotes are likely low, although field-testing should be used to confirm.