April 2020
This is the final report abstract for POP2018-05: Westland petrel population size estimate


The density and distribution of Westland petrel burrows was assessed over a 12-year period, forming the baseline population estimate for the endangered Westland petrel at around 6,200 breeding pairs in 2019 and a world population of between 13800 - 17600 individuals for the areas surveyed.

Density transects were conducted in 2007 - 2011 to establish the location and density of 17 colonies of the petrels nesting in rugged untracked terrain in Paparoa National Park, West Coast, New Zealand. During 2014 – 2018, major storms caused widespread treefall and landslides, destroying breeding habitat throughout the species’ breeding range.

The surveys were repeated at the most accessible colonies in 2012 – 2017, and in a comprehensive survey in 2019 covering 95% of the estimated population. Burrow density has increased over the 12-year timeframe, and this was commensurate with a 1.022% annual increase (0.971 – 1.076: 95% Credibility Interval) in the population from Mark Recapture data from the demography study area. Demographic influences of the major, and ongoing habitat loss may be continuing, as birds re-established nests and partnerships following loss of their habitat in areas of landslips and treefall in major storms in 2014 and onwards.

The study presents a picture of the complex effects of climate-related disruption to the biology of a long-lived species. There is an expected increase in the frequency of severe weather events including ex-tropical cyclones and abnormal fluctuations in sea surface temperatures associated with climatic change. With a single nesting area in the West Coast region is vulnerable to landslips and treefall, it is likely that climate change will have an ongoing, negative influence of Westland petrel breeding habitat. Current indications from the demographic study suggest that the species has some flexibility to adapt and to occupy new colony areas following habitat disturbance.

Publication information

Waugh, S., Barbraud, C., Delord, K., Simister, K., Baker, G., Hedley G., Wilson, K., Rands, D. 2020. Changes in population density and response to storm damage for Westland petrels 2007 – 2019. Report prepared for the Conservation Services Programme, Department of Conservation published in Marine Ornithology 48: 273-281. 


Conservation Services Programme
Department of Conservation
PO Box 10-420
Wellington 6143


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