In New Zealand, the toxin sodium fluoroacetate (compound 1080) is used to reduce numbers of introduced brushtail possums (Trichosurus vulpecula) to enhance forest condition and reduce bovine tuberculosis (Tb) infection in livestock. However, there is concern that the use of toxins may cause mortality in non-target species. We investigated the effect of possum control using aerially applied cereal baits containing 1080 on 36 radio-tagged South Island fernbirds (Bowdleria punctata punctata) in winter 2010. During monitoring, five fernbirds dropped their transmitters, one was killed by a predator and three died of 1080 poisoning (a mortality rate from 1080 poisoning of 9.4%, 95% CI 0 2.4Á22.6%). This study suggests that acute impacts of aerial 1080 operations on fernbird numbers are small and the observed impact could be outweighed by improved productivity and survival resulting from the reduction of impacts caused by introduced mammalian predators that die from 1080 poisoning.