Tiare Varela Valentina Colodro T.J. Clark-Wolf Jonathan J. Felis Peter Hodum Francisco Javier Astete Castillo Veronica Lopez Ryan D. Carle 2024 <div class="abstract"><div>Species population estimates are a fundamental component of conservation planning, but there are deficiencies in reliable data for many seabirds. The Pink-footed Shearwater<span>&nbsp;</span><i>Ardenna creatopus</i><span>&nbsp;</span>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<span>&nbsp;</span>study area was 0.0106 burrows·m^-2<span>&nbsp;</span>(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&nbsp;209 burrows (95% confidence interval [CI] = 74&nbsp;715-261&nbsp;704, coefficient of variation [CV] = 0.28), and 127&nbsp;503 breeding pairs (95% CI = 87&nbsp;610-167&nbsp;395). The model-based method estimated 233&nbsp;436 burrows (95% CI = 151&nbsp;237-332&nbsp;179, CV = 0.19) and 181&nbsp;859 breeding pairs (95% CI = 95&nbsp;773-267&nbsp;945, CV = 0.24). These population estimates are greater than previous estimates for Isla Mocha, whose means ranged from 19&nbsp;440-42&nbsp;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.</div></div> application/pdf en Maine Ornithology Breeding population size of the Pink-footed Shearwater Ardenna creatopus on Isla Mocha, Chile article