Proceedings of the Vertebrate Pest Conference

Aerial application of brodifacoum bait for eradication of invasive rodents from islands raises concerns about environmental contamination and adverse effects on nontarget wildlife. We summarize results of environmental monitoring for brodifacoum residues after New Zealand eradications in a fenced reserve at Maungatautari and on the offshore islands Little Barrier, Rangitoto, and Motutapu. Brodifacoum was not detected in extensive freshwater monitoring at Maungatautari, or in freshwater samples from Little Barrier Island. Residual concentrations were present in soil samples from underneath degrading bait pellets on Little Barrier, and decreased to near the limit of detection by c. 100 days after application. No brodifacoum was present in marine shellfish sampled from Little Barrier, Rangitoto or Motutapu. A range of birds, including a kiwi from Little Barrier, were considered nontarget mortalities. Nine little blue penguins found dead on beaches outside the Rangitoto/Motutapu area after baiting were considered most likely to have died of starvation, despite the detection of brodifacoum in three birds. This result highlights the critical role of post-application environmental monitoring in rodent eradications, and information gaps regarding the movement, persistence, and effects of brodifacoum in the environment.