New population estimate for an abundant marine indicator species, Rako or Buller’s Shearwater (Ardenna bulleri)

ABSTRACT

Accurate and repeatable population estimates are key to establishing population trends and conservation status. Rako, or Buller’s Shearwater (Ardenna bulleri) is a seabird endemic to New Zealand that breeds only on the Poor Knights Islands, but forages throughout wider areas of the Pacific Ocean during the non-breeding season. The lack of threats on the breeding grounds and the wide foraging range of Buller’s Shearwaters makes them ideal sentinels of ocean health. Although they are commonly seen at sea and the population in the 1980s was thought to be around 2.5 million birds, other rapid land-based surveys suggested a much lower figure (~100,000 pairs on Aorangi), and no thorough population estimate has been undertaken to date. We calculated a population estimate for Buller’s Shearwater based on burrow counts and state of occupancy conducted at the Poor Knights during either the 2016–2017 or the 2017–2018 breeding seasons. We incorporated information on habitat availability and preference in population models. Our estimate of 78,645 (95% confidence interval 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 potentially important marine indicator species.

KEYWORDS:

• Seabird
• population estimate
• marine indicator
• Procellariiformes
• Buller’s Shearwater

Acknowledgements

All research on the islands was conducted under the Wildlife Act Authority 38016-FAU. We thank the New Zealand Department of Conservation for Research and Landing permits and Ngātiwai for supporting research within their rohe. This research was financially supported by the Birds New Zealand Research Fund, the Museum of New Zealand Te Papa Tongarewa and Landcare Research. We thank Dive Tutukaka for their logistical support with boat transfers to and from the islands. We are grateful to the many field volunteers who made this research possible, including: Jane Gardiner, Cathy Mitchell, Jingjing Zhang, Rachael Sagar, Neil Fitzgerald, Tim Neill, Glenn McKinlay, Kate McConnell, Shelley Heiss-Dunlop, Stephanie Borrelle, Edin Whitehead and Annika Andreson.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Birds New Zealand Research Fund, the Museum of New Zealand Te Papa Tongarewa and Manaaki Whenua- Landcare Research.