Agreement on the Conservation of Albatrosses and Petrels

79 000 active Buller’s Shearwater burrows counted on New Zealand’s Poor Knights Islands

Bullers Shearwater off Mercury Islands MZ Kirk Zufelt
Buller's Shearwater off Mercury Islands, New Zealand; photograph by Kirk Zufelt

 Megan Friesen (Northern New Zealand Seabird Trust, Auckland, New Zealand) and colleagues have published in the journal Emu – Austral Ornithology on a breeding census of the globally Vulnerable and nationally Naturally Uncommon Buller’s Shearwaters Ardenna bulleri.

The paper’s abstract follows:

“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.”


Friesen, M.R., Simpkins, C.E., Ross, J., Anderson, S.H., Ismzar-Rebitz, S.M.H., Tennyson, A.J.D., Taylor,G.A., Baird, K.A. & Gaskin, C.P. 2021.  New population estimate for an abundant marine indicator species, Rako or Buller’s Shearwater (Ardenna bulleri).  Emu – Austral

John Cooper, ACAP Information Officer, 02 September 2021