Capturing the imminent extinction of a kakaruai/South Island robin population

The fragmentation of forested environments in Aotearoa | New Zealand has resulted in many small, geographically isolated populations that face an increased risk of extinction. However, population extinction itself, and its proximate causes, are rarely witnessed scientifically. As part of a broader study, we assessed the population status of a remnant kakaruai (South Island robin; Petroica australis) population within the Ōtepoti | Dunedin area. We compared parameters of this remnant population at Silver Stream (no recent predator control) with a translocated population at Orokonui Ecosanctuary (a fenced mainland ecosanctuary). Specifically, we indexed the abundance of mammalian predators and invertebrate biomass and monitored breeding behaviours and nesting outcomes in the spring and summer of 2022–2023. The Silver Stream population has now almost completely disappeared; we located a single female, resulting in a 10:1 male-biased sex ratio. We did not detect any difference in invertebrate biomass between Silver Stream and Orokonui, where the kakaruai population is thriving. Mean rat tracking was between 2% and 27% at Silver Stream, whereas only mice were detected at Orokonui. Rats have most likely contributed to the decline of the Silver Stream population as they target incubating females on nests. Our results emphasise that the decline of native forest birds is ongoing, and local extinction is imminent in the Silver Stream kakaruai population in the absence of predator management. Failure to prevent this local extinction may result in the loss of one of only two remaining populations of kakaruai on the east coast of Te Wai Pounamu | the South Island.