Grant Macdonald's Sentinel-1 radar tracking follows emperor penguin colonies through the Antarctic winter
Durham University geographer Grant Macdonald and colleagues used European Space Agency Sentinel-1 radar imagery, which does not need sunlight, to follow three emperor penguin colonies through the dark Antarctic winter from 2017 to 2024. The Atka Bay colony moved onto glacier ice in early spring in seven of the eight years even though the sea ice stayed stable, a pattern the team says needs further study.
Science··Evening
Radar imagery reveals moving penguin colonies through the dark
Durham University geographer Grant Macdonald and his team used the European Space Agency's Sentinel-1 synthetic aperture radar satellite, which sends microwave pulses to the surface and measures their return rather than relying on sunlight, to track emperor penguin colonies through the dark Antarctic winter for the first time. While reviewing radar images of a colony site, the team noticed a bright cluster of pixels moving against an otherwise stable, dark background of sea ice, a pattern that did not match features such as icebergs or rough ice, which stay fixed once the sea ice is stable for the season. The same bright, moving pattern turned up at other known colony locations, and the team confirmed it was the penguins themselves by comparing the radar images against optical satellite images captured once sunlight returned in September.[1], [2]
Eight years of tracking turn up an unexplained spring shift
Macdonald's team combined the winter radar images with medium-resolution optical images from spring and summer to follow three of the largest colonies, at Atka Bay, Coulman Island and Cape Washington, across eight years from 2017 to 2024. The colonies were typically less mobile during the winter and spread out over greater distances once spring and summer arrived. The Atka Bay colony stood out: in seven of the eight years, it moved from the sea ice up onto the glacier ice flowing from the continent in early spring, even though the sea ice itself, the species' usual preferred habitat, remained stable at the time. Macdonald writes that the team does not yet understand why this shift happens and that it needs further research.[1]
The tracking method arrives as sea ice instability deepens
Satellite tracking of emperor penguins by daylight images has been possible since 2009, when researchers first learned to spot colonies by the dark guano stains they leave on snow and ice, a method that has since helped researchers identify many additional colonies. Antarctic sea ice has declined markedly since 2016 and, researchers say, has likely entered a new state marked by lower extent and greater instability. Earlier in 2026 the International Union for Conservation of Nature added emperor penguins to its list of endangered species, citing projected declines in sea ice as the main driver. Extending satellite tracking through the winter, when colonies were previously invisible to observation, gives researchers a year-round view of the species during exactly the season when sea ice conditions matter most to its breeding cycle.[2], [1]
