Effects on South Island robins (Petroica australis) from pest control using aerially applied 1080 poison

New Zealand robins are thought to be vulnerable to poisoning by sodium fluoroacetate (1080), because individual birds found dead after aerial pest control operations have tested positive for 1080. We investigated the impacts of an aerial 1080 operation (preceded by non-toxic prefeeding) to control brushtail possums (Trichosurus vulpecula) on the survival and breeding success of a robin population at Silver Peaks, Dunedin environs, South Island, New Zealand. We monitored the survival of individual marked robins and their nesting success before and after the 1080 application. Robins were also monitored at a non-treatment site at nearby Silverstream. The possum control operation at Silver Peaks reduced rats (Rattus rattus), possums and mice (Mus musculus) to very low numbers, which remained low for at least 3 months. In contrast, at Silverstream, pest numbers remained high throughout the study. All individually colour-banded robins monitored in the treatment area (n = 19) plus five unbanded territorial birds were resighted post-drop, indicating that no known birds died as a direct result of the poison application. Nesting success in the treatment area, measured as daily survival rate, was higher than in the non-treatment area, and did not significantly differ between the breeding seasons before and after the poison drop. Our study showed that the 1080 operation did not adversely affect the robin population at Silver Peaks, but did reduce important nest predators (rats and possums) to low levels. Although there was no evidence of a positive indirect impact on nesting success through the reduction in predators, rat and possum abundances were relatively low at Silver Peaks (cf. Silverstream) prior to the 1080 drop, and vary from year to year. We recommend continued monitoring over several seasons to ascertain whether 1080 operations have any long-term benefits for robins at Silver Peaks.