Using multiple abundance estimators to infer population trends in Atlantic Puffins

Abstract

We used five techniques to estimate the number of Atlantic Puffins (Fratercula arctica) using a study plot on Gull Island, Newfoundland, during the 2000 breeding season. Grubbing of burrows yielded an estimate of a breeding population of 522 (95% CI: 364–668) Atlantic Puffins on this plot. Attendance counts of birds standing on the plot consistently underestimated the breeding population. A closed-population estimator with sighting heterogeneity estimated that of the 535 Atlantic Puffins banded since 1997, 370 (336–404) used the plot in 2000. Using 370 birds as the marked population, a corrected Lincoln–Petersen index estimated a total population of 1712 (1233–2191) based on captured birds. Based on resights of birds, ratios of banded birds to total attendance estimated 2927 (2608–3335), and the Bowden estimator gave 3502 (3054–3950) Atlantic puffins. We projected an age-based matrix using literature values, and extracted the proportions of nonbreeding birds and young birds expected at a stable age distribution and compared the proportions with observed values. Based on the large number of nonbreeders suggested by the abundance estimates, we suspect that this population (i) is stable or increasing, (ii) includes breeding-age Atlantic Puffins that do not breed, and (iii) has been enjoying high fecundity in recent years.