LAUSR

Invasive species are a leading cause of native biodiversity loss. In Australia, the toxic, invasive cane toad Rhinella marina has caused massive and widespread declines of northern quolls Dasyurus hallucatus. Quolls are fatally poisoned if they mistakenly prey on adult toads. To prevent the extinction of this native dasyurid from the Top End, an insurance population was set up in 2003 on two toad-free islands in Arnhem Land. In 2015, quolls were collected from one of these islands (Astell) for reintroduction. We used conditioned taste aversion to render 22 of these toad-na€ıve quolls toad averse. Seven quolls received no taste aversion training. The source island was also predator-free, so all quolls received very basic predator-aversion training. In an attempt to reestablish the mainland population, we reintroduced these 29 northern quolls into Kakadu National Park in northern Australia where cane toads have been established for 13 years. The difference in survival between toadaverse and toad-naive quolls was immediately apparent. Toad-naive quolls were almost all killed by toads within 3 days. Toad-averse quolls, on the other hand, not only survived longer but also were recorded mating. Our predator training, however, was far less effective. Dingo predation accounted for a significant proportion of toadsmart quoll mortality. In Kakadu, dingoes have been responsible for high levels of quoll predation in the past and reintroduced animals are often vulnerable to predation-mediated population extinction. Dingoes may also be more effective predators in fire degraded landscapes. Together, these factors could explain the extreme predation mortality that we witnessed. In addition, predator aversion may have been lost from the predator-free island populations. These possibilities are not mutually exclusive but need to be investigated because they have clear bearing on the long-term recovery of the endangered northern quoll.