Conditioned taste aversion enhances the survival of an endangered predator imperilled by a toxic invader.
Even when we cannot eradicate an invasive species, we may be able to reduce its ecological impact. In Australia, a critically endangered predator, the northern quoll Dasyurus hallucatus is threatened by the invasion of the highly toxic cane toad Bufo marinus. Following toad invasion, quoll populations have become extinct across Northern Australia. Toads are continuing to spread, and will soon invade the Kimberley, one of the quoll's last strongholds. To prevent future local extinctions, we need a new approach for mitigating the impact of cane toads on this iconic predator. We investigated whether conditioned taste aversion (CTA) could be used to modify quoll predatory behaviour and mitigate toad impacts. We successfully induced an aversion to live toads in juvenile northern quolls by feeding them a dead toad containing a nausea-inducing chemical (thiabendazole). To investigate whether CTA enhanced quoll survival, we fitted radiocollars to 31 toad-smart and 31 toad-naïve quolls, and monitored their survival after reintroduction to the wild. We analysed telemetry data using the program MARK to investigate whether survival was influenced by sex or experimental treatment (toad-smart vs. toad-naïve). Five of 17 (29%) toad-naïve male quolls died shortly after release, as soon as they encountered and attacked large cane toads. In toad-naïve quolls, apparent survival rates were higher for females (0.84) than for males (0.58), reflecting a sex difference in the propensity to attack toads. In both sexes, toad-smart quolls had higher apparent survival rates than did toad-naïve conspecifics (mean daily apparent survival rates for females, 0.94 vs. 0.84 respectively; for males, 0.88 vs. 0.58). Synthesis and applications. Wildlife managers could aerially deploy taste aversion baits in the field, ahead of the toad invasion front, to teach toad-naïve quolls to avoid live cane toads before the toads invade such areas. This approach has wider applications, and could also be used to mitigate the impacts of invasive vertebrate predators on threatened fauna. When invasive predators cannot be eradicated, CTA may provide a feasible way to maintain populations of endangered fauna in the presence of the invader.