---
title: "Breeding survey of Pink-footed Shearwaters on Isla Mocha, Chile"
---

# Breeding survey of Pink-footed Shearwaters on Isla Mocha, Chile

*![Grisselle Chock Pink footed Shearwater watercolour gouache Peter Hodumjpg](https://www.acap.aq/images/stories/acap/Birds/Shearwaters/Pink_footed/Grisselle_Chock_Pink-footed_Shearwater_watercolour_gouache_Peter_Hodumjpg.jpg)Pink-footed Shearwater, gouache watercolour for ACAP by [ABUN](https://abun4nature.org/) artist, Griselle Chock, after a photograph by Peter Hodum*

 Ryan Carle ([Oikonos-Ecosystem Knowledge](https://www.oikonos.org/), Santiago, Chile) and colleagues have published in the online journal *[Marine Ornithology](http://www.marineornithology.org/)* on a breeding survey of the [Vulnerable](https://datazone.birdlife.org/species/factsheet/22698195) and ACAP-listed Pink-footed Shearwater *Ardenna creatopus.*

 The paper’s abstract follows:

 “Species population estimates are a fundamental component of conservation planning, but there are deficiencies in reliable data for many seabirds. The Pink-footed Shearwater *Ardenna creatopus* is a seabird that breeds on three islands worldwide, with the largest population on Isla Mocha, Chile. We aimed to update the breeding population estimate of Pink-footed Shearwaters on Isla Mocha, comparing results from design- and model-based estimation methods. We counted shearwater burrows in 220 randomly generated five-meter-radius plots across pre-defined strata on Isla Mocha. We estimated total number of burrows using area-based extrapolation (design-based method), and separately using a model predicting burrow density based on habitat (model-based method). We multiplied burrow abundance estimates by burrow occupancy for final population estimates. The stratum-area-weighted burrow density estimate for the 15.8 km2 study area was 0.0106 burrows·m-2 (standard error [SE] = 0.0030). The average island-wide proportion of occupied burrows was 0.758 (standard deviation [SD] = 0.121). The design-based method estimated 168 209 burrows (95% confidence interval [CI] = 74 715-261 704, coefficient of variation [CV] = 0.28), and 127 503 breeding pairs (95% CI = 87 610-167 395). The model-based method estimated 233 436 burrows (95% CI = 151 237-332 179, CV = 0.19) and 181 859 breeding pairs (95% CI = 95 773-267 945, CV = 0.24). These population estimates are greater than previous estimates for Isla Mocha, whose means ranged from 19 440-42 095 breeding pairs. Because our study design differed from those used to generate previous estimates, our estimate should be considered a stand-alone result rather than an increase in the breeding population. Because of the low fit of the model-based result, the design-based result may be a more reliable estimate to use for species management efforts. Based on our estimate, approximately 90% of the Pink-footed Shearwater world population breeds on Isla Mocha, and with its restriction to only three breeding localities world-wide, the species remains vulnerable. The full manuscript in Spanish can be found in Appendix 1, available on the website.”

 **Reference:**

 Carle, R.D, Varela, T., Colodro, V., Clark-Wolf, T., Felis, J., Hodum, P., Astete Castillo, F.J. & López, V. 2024.  Breeding population size of the Pink-footed Shearwater *Ardenna creatopus* on Isla Mocha, Chile.  *[Marine Ornithology](http://www.marineornithology.org/article?rn=1571)*[52: 85-96](http://www.marineornithology.org/article?rn=1571).

 *22 May 2024*