A seasonal decomposition of the estimated size of a penguin population at Phillip Island, Australia

Modern non-parametric methods allow the estimation of a population size under weaker conditions than the classical methods if there are frequent capture occasions. Here a non-parametric estimate of the number of penguins occupying Summerland Beach, Phillip Island, Australia, was computed. This estimator did not assume equal catchability of individuals, did not assume a parametric form for the population size as a function of time and allowed individuals to leave and re-enter the population. The resulting estimate was then decomposed into a seasonal component and a trend component using seasonal time series models to facilitate the understanding of the changes in the population size. The estimated seasonal effects quantified the difference between the number of penguins in the breeding and non-breeding season, and the trend component indicated an increase in the population size over the period of the study. The estimates of the number of penguins are shown to be consistent with other estimates obtained from a variety of sampling methods and statistical analyses.