Impacts of pathogenic disease and native predators on threatened native species

Low (this issue) makes two key points in his paper ‘Which factors limited stitchbird population growth on Mokoia Island?’ First, that while aspergillosis has been suggested to explain the high adult mortality rates of hihi (stitchbirds, Notiomystis cincta) on Mokoia Island in comparison with Tiritiri Matangi Island, this hypothesis is not supported by conclusive evidence. Second, that the high density of ruru (morepork, Ninox novaeseelandiae) on Mokoia when hihi were there (1994–2002) provides a plausible alternative hypothesis for the low adult survival. He is correct on both points, and his paper raises important issues not only for management of hihi, but for future management of other New Zealand species. Here we provide additional information to clarify and extend Low’s observations, and briefly discuss the wider relevance of these issues to threatened species management.