Trends in density, abundance and response to storm damage for Westland petrels Procellaria westlandica 2007-2019

International audience; The density and distribution of Westland Petrel burrows was assessed over a 12-year period (2007–2019). During that time, burrow densityincreased while occupancy remained stable, commensurate with an annual population growth rate of 1.022 (95% confidence interval:0.971–1.076), as estimated using mark recapture data. From our surveys, we estimated a 2019 baseline population of ~6 200 breeding pairsand a world population of 13 800–17 600 individuals, covering around 95% of the population. Transects were conducted to establish thelocation and density of 17 petrel sub-colonies in rugged, untracked terrain in Paparoa National Park, West Coast, New Zealand. Major stormsin 2014–2018 caused widespread treefall and landslides, destroying breeding habitat throughout the species’ breeding range. Demographiceffects of the major and ongoing habitat loss may continue in the medium to long term, as birds re-establish burrows and partnershipsfollowing loss of their habitat. Our study illustrates the complex effects of climate-related disruption on the biology of a long-lived species.With a single nesting area in the West Coast region, climate change will likely have an ongoing influence on the species’ global population,since an increase in the frequency of severe weather events, including ex-tropical cyclones, is expected. However, current indications suggestthat the species has some flexibility to adapt and to occupy new areas following habitat disturbance.