Energy expenditure of Ad elie penguins during the breeding season: females pay the cost in years of low food availability

Abstract

Changes in prey availability can lead to mismatches between consumers and resources, decreasing the fitness of consumers, especially during periods of high energy demand such as reproduction. We investigated interseasonal variation in the foraging behaviour of chick-rearing Ad elie penguins, Pygoscelis adeliae, in a declining colony in the West Antarctic Peninsula to assess the impact of changes in prey abundance. Specifically, we analysed how these changes affect the energetic cost of males and females during the breeding season. Using information from foraging trips, diet, body condition and daily energy expenditure of 38 Ad elie penguins breeding in Ardley Island, King George Island, in 2019/2020 and 2021/2022, we found that during low food availability conditions, penguins were forced to increase their foraging effort and their body mass was lower. Specifically, females extended their foraging trips, resulting in 40% higher energy expenditure compared to a year with high prey availability. We observed no significant changes in physiological condition, breeding success or trophic niche. The lower fat reserves and higher energy expenditure of females during the breeding season with low food availability may render them more vulnerable to the challenging conditions of the winter season, with potential negative consequences on population trends.