Effects of an island-wide rodent eradication programme on two threatened bird species

Abstract

Context For the past 50 years, rodent eradications have been conducted worldwide to reverse the devastating impacts of introduced rodents on island species. However, few studies have quantitatively measured the effects of rodent eradications on native species. Aims This study investigated the effects of a rodent eradication on Lord Howe Island on two native birds. Methods To mitigate the risk of Lord Howe currawongs being poisoned during baiting operations, 30–40% of the population were taken into captivity during baiting, while the remaining currawongs were left in the wild. We studied currawong survival, nesting density and breeding success pre- and post-eradication to test how the baiting, a period in captivity, and the removal of rodents affected currawongs. We also investigated breeding success of white terns as they were expected to benefit from the eradication due to predator reduction. Key results We found that many currawongs left in the wild disappeared during the baiting period and nesting densities in one part of the island were significantly lower after the eradication. These currawongs likely died of poisoning as they were not resighted for 2 years post-eradication. White tern breeding success did not increase after the rodent eradication, although their predators were largely eliminated. Conclusions The captive management of currawongs mitigated the adverse effects of the baiting. As those currawongs that survived had high breeding success, we predict that the population will soon recover to pre-eradication size. Implications Our study reinforces the necessity of integrating ecological monitoring as part of future eradications on islands.

The animal welfare, environmental impact, pest control functions, and disease effects of free‐ranging cats can be generalized and all are grounds for humanely reducing their numbers

“…On islands, cat predation sometimes checks rodent predation on breeding seabirds (Rayner et al, 2007). In these cases, management should target both cats and rodents (Portelli & Carlile, 2020; Segal et al, 2022).…”