Protection and mortality of non-target terrestrial bird species during the eradication of rodents on Lord Howe Island

Abstract

To eliminate the destructive impact of rodents on islands, conservation practitioners commonly use rodenticides to eradicate these pests. Frequently used rodenticides, such as brodifacoum, are non-specific. Consequently, non-target species may be susceptible to the poison. While mitigation actions to protect against unwanted impacts on non-target species are often included in eradication planning, such impacts are rarely measured or reported. In 2019, a rodent eradication program was implemented on Lord Howe Island to remove ship rats and house mice. To protect the island’s unique suite of endemic avian fauna, a comprehensive monitoring and mitigation plan was implemented. Following assessments of potential effects of baiting on island-species, two endemic species were taken into captive management during the eradication. To assess effects on other species, a total of 243 ha of bushland was searched over a 14-week period and an additional 190 ha was searched in the island’s settlement area for carcasses of non-targets. These surveys found that buff-banded rails suffered the highest level of mortality, but few carcasses of endemic species were found. The captive management program was successful with more than 95% of individuals that were taken into captivity being released at the end of the program. Post-eradication surveys of captive-managed species have shown that the endemic woodhen population has increased by nearly five-fold on pre-eradication levels and that endemic currawong numbers have also increased. Surveys of other bush birds have found higher numbers for most species and shows that pre-eradication assessments of these species being at lower risk were appropriate.