BREEDING POPULATION SIZE OF THE PINK-FOOTED SHEARWATER ARDENNA CREATOPUS ON ISLA MOCHA, CHILE

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 km(2) study area was 0.0106 burrowsm (-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.