Year-round movement of emperor penguin colonies observed from space.

Emperor penguins are threatened by climate change and their population is predicted to decline rapidly this century due to changes in Antarctic sea ice. Remote sensing is a key tool for monitoring emperor penguins but analysis has been restricted to spring/summer due to a lack of optical imagery during the polar night. Here we show Sentinel-1 synthetic aperture radar (SAR) can be used to observe the movement of penguin colonies throughout winter. We combine winter SAR imagery with medium-resolution summer optical imagery to track the year-round movement of colonies at Atka Bay, Coulman Island, and Cape Washington, 2017-2024. Although emperor penguins are less mobile than during summer, all three colonies exhibit movement in winter, but which varies between years and colonies. At times, different groups within the colonies synchronously move away from the fast ice edge despite its apparent stability. We demonstrate that SAR is an important tool for understanding emperor penguin behaviour throughout their breeding cycle, and particularly their response to environmental forcing and change during winter.