The current trajectory of king penguin (Aptenodytes patagonicus) chick numbers on Macquarie Island in relation to environmental conditions

Abstract

Abstract Macquarie Island's king penguin (Aptenodytes patagonicus) population has changed dramatically over recent centuries. Following near decimation from commercial exploitation during the 19th and early 20th centuries, chick numbers increased rapidly from 1930–1980. Since then, the population's trajectory has remained unreported, and environmental factors potentially influencing the population are poorly understood. From 2007–2020, king penguin chicks were censused annually. Chick numbers fluctuated between years, ranging from 33,513–78,714. Overall, the numbers decreased at 1.06 ± 0.03% per annum. While further studies are required to infer causality, annual chick numbers were negatively correlated with environmental conditions on land and at sea. Heavy rainfall, total rainfall, and maximum east coast wave height during incubation correlated with fewer chicks that year. Warmer sea surface temperatures in the foraging region of adult king penguins during incubation and early chick-rearing also correlated with lower chick numbers. While interannual variability and the long generation time of king penguins makes it unclear if the decrease in chick numbers represent a decrease in the breeding population, it is clear the late 20th century rapid increase in Macquarie Island's breeding population has ceased. Ongoing monitoring will establish if this is indicative of the population stabilising or an ongoing population decline.