Winter sea-ice decline drives gentoo penguin population expansion along the western Antarctic Peninsula

Gentoo penguin Pygoscelis papua populations have expanded rapidly along the western Antarctic Peninsula (WAP), but the role of winter sea-ice changes in driving this growth remains unclear. To address this, we used a novel, 5 decade long satellite-derived sea-ice data set (1979-2023) to examine how annual variation in winter sea-ice extent, concentration, persistence, and winter open water frequency affects gentoo penguin population growth rates. Our analysis identified significant declines in winter sea-ice extent and concentration, paired with an increase in winter open water days across the entire WAP region. Gentoo penguin population growth is inversely correlated with winter sea ice, suggesting that increased winter open water availability facilitates expanded winter foraging opportunities. These findings highlight the importance of winter sea-ice dynamics in shaping Antarctic marine ecosystems and underscore the need for observation systems capable of monitoring Antarctic sea ice at high resolution even through the Antarctic winter period.