Assessing gaps in reporting non-target mortality in island rodent eradication operations

Eradicating invasive species is a key part of island restoration, and can reverse the devastating impacts on native biota. Rodents are one of the most widespread invasive species, found on 80% of oceanic island systems, but have been removed from hundreds of islands through the application of anticoagulant-treated cereal bait. While such eradication operations are often net positive events for island ecosystems over the long-term, some native biota are also susceptible, resulting in short-term non-target mortality. One of the most widely distributed groups of birds, rails and allies (Rallidae) are highly adaptable, often endemic, and are known often to suffer mortality during rodent eradication operations, to varying degrees. Our goal was determine if the year of eradication or the size of the island predicted whether non-target mortalities were reported, including those that were true absences of mortality. We examined 122 eradication operations on 81 islands with rails present from 1983 to 2015, and found 78% with no reported information on non-target mortality using our search criteria. We found non-target mortality reporting has decreased over time, and there was no relationship with island size. Post-operational monitoring of eradication operations should thoroughly record non-target mortality to improve our understanding of factors affecting non-target mortality, and the efficacy of mitigation measures.