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

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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.

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