Evidence of emperor penguins' sensitivity to sea ice fluctuations

Using satellite-derived abundance indices over 20 years, we investigated population change among the seven Ross Sea emperor penguin (Aptenodytes forsteri) colonies. We found a 90% probability that the Ross Sea metapopulation had lower springtime attendance between 2005 and 2024 (mean change = -23%; 95% CI: -46 to +20%). We identified two distinct phases of change: slightly increasing 2005 to 2019/2020, followed by a steep decline 2020-2024, resulting in a decrease of approximately 23 000 birds in 5 years or approximately 32% of the regional population. Over the 20 years, the two southernmost colonies, Cape Crozier and Cape Colbeck, increased in size, yet Beaufort, Coulman, Roget and Washington declined, resulting in a negative population trend especially evident from 2021. Asynchronous population change suggests metapopulation dynamics, with immigration from western colonies possibly driving increases at Colbeck and Crozier. Winter and spring sea ice concentration anomalies (5 year lag) and El Niño phases (1 year lag) statistically explained the most variance in our time series. Our results indicate that emperor penguins may be sensitive to sea ice fluctuations, offering insight into how this species may have adapted throughout their history and emphasizing the need for timely re-evaluation of targeted conservation strategies in an era of sea ice change.