Rako / Buller's shearwater (Ardenna bulleri) is endemic to the Poor Knights Islands and wider Hauraki Gulf. The first quantified population estimate for Buller’s shearwater was based on burrow counts and state of occupancy during surveys conducted at the Poor Knights in the 2016-2017 and 2017-2018 seasons. Information on habitat availability and preference were incorporated in the population models. The estimate of 78,645 (67,176 – 89,178) active burrows, broadly representing breeding pairs, is lower than some previously published assessments. This is a repeatable quantitative study of the Buller’s shearwater breeding population, including breeding activity, and provides critical baseline data to determine population trends for this species. A baseline for breeding success was also established.

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This survey on Tawhiti Rahi and Aorangi, and subsequent surveys conducted on Tawhiti Rahi, showed that while the population estimate established was lower than expected, the species is not currently at carrying capacity on the islands due to the large number of survey plots on the islands where there were inactive burrows or no burrows at all. Observations since, also suggest a sizeable non-breeding population, potentially a mix of non-breeders (possibly some breeders skipping a year) and pre-breeders. We will repeat this population survey, returning to Tawhiti Rahi and Aorangi in the 2023-2024 season.