Using bioindicators to inform effective predator management for threatened species protection

In Australia, most threatened species translocations conducted into areas where feral predators are present fail to establish viable, self-sustaining populations despite intensive predator control. These translocations are occurring amidst a lack of understanding regarding the conditions required for native species to survive, including predator densities. This study investigated whether population trends of in situ common species could be used as bioindicators to determine the effectiveness of predator management for threatened species protection. We compared changes in capture rates of four small mammals and four reptile species inside and outside a predator-proof reserve for 11 years after cat and fox removal to identify which species responded to cat and fox eradication at various time scales. We only used sites inside the reserve where threatened species had not yet been reintroduced to isolate the effects of cat and fox removal. The effectiveness of these bioindicators was then tested at an unfenced reserve where predators were controlled using baiting, trapping, and shooting. There was a significant increase in the abundance of native rodents (spinifex hopping mouse and Bolam's mouse) inside the fenced reserve compared to outside, however, these differences were not detected in the unfenced reserve possibly due to inadequate predator control or insufficient time for in situ species to recover with sustained predator control. Captures of the introduced house mouse were higher at sites inside the fenced reserve in some years, but the difference was not consistent. Native dunnarts and all four reptile species did not respond consistently over the 11-year time frame at either reserve. Native rodent abundance was the best indicator of effective feral predator control and may provide a useful bioindicator for threatened species management, such as reintroductions.