Fate of moreporks (Ninox novaeseelandiae) during a pest control operation on Mokoia Island, Lake Rotorua, North Island, New Zealand

We monitored 16 radio-tagged moreporks (Ninox novaeseelandiae) on Mokoia Island after a brodifacoum poison drop to eradicate mice (Mus musculus), normally included in the owls' diet. All 16 moreporks were alive after 13 days. One bird was found dead on day 22, and corpses of two radio-tagged birds were located on day 51. The bird found on day 22 contained 0.97 mg kg(-1) of brodifacoum in its liver. The other two carcasses were not analysed, but they probably died as a result of brodifacoum poisoning. Thus, three out of 14 birds died (21% mortality). A further eight banded and six non-banded birds were also monitored. Of these, 50% were not seen following the drop. Secondary poisoning is implicated in the disappearance of these birds. Sublethal effects such as lowered breeding success and stress may have affected morepork over a prolonged period following the poisoning operation. Further studies are needed to investigate the exact pathway of this poison, especially the potential for invertebrates to carry poison.