Summary:
Satellite images of Antarctica have led scientists to an unexpected discovery about emperor penguins, revealing a new risk tied to shrinking sea ice. In a study published in Communications Earth & Environment, researchers from the British Antarctic Survey report the first identification of emperor penguin moulting sites using medium and very-high-resolution satellite imagery.
Moulting – the annual process in which penguins replace their feathers with new waterproof plumage – is a critical stage in their life cycle. During this period, the birds cannot enter the ocean to feed and depend on stable sea ice as a platform. By analysing satellite data from 2019 to 2025 in Marie Byrd Land, West Antarctica, the team identified more than 100 groups of moulting penguins on coastal fast ice. However, between 2022 and 2024, when Antarctic sea ice extent fell to record lows, fast ice coverage in the region dropped sharply, concentrating penguins into smaller areas.
In several cases, the ice broke up before moulting was complete, likely forcing birds into the ocean prematurely. The findings raise concerns that adult mortality linked to sea ice loss may pose a greater long-term threat to emperor penguin populations than previously understood.
— Press Release —
Accidental discovery reveals grim future for emperor penguins
Researchers from British Antarctic Survey discovered several moulting colonies by chance, after spotting distinctive brown patches along the coastline of an area of Antarctica called Marie Byrd Land. The timing matched up with when emperors should have been moulting, prompting the team to take a closer look.
Until now, researchers have known little about where emperor penguins go to moult – the annual process where the birds replace their feathers with new, waterproof plumage. This study marks the first time scientists have observed moulting colonies using satellite images.
By comparing the location and timing of moulting with changing sea ice conditions, the team discovered that shrinking sea ice is forcing penguins into increasingly crowded groups, with potentially catastrophic consequences for their survival if the ice breaks up early.
What the satellites revealed
Each summer, emperor penguins from the Ross Sea in West Antarctica migrate as much as 1,000 km to Marie Byrd Land to find stable sea ice on which to moult. This population consists of seven breeding colonies accounting for up to 40% of the global population. Historically, Marie Byrd Land, is one of the few areas that retains its fast sea ice – sea ice attached to the coast – throughout the year.
By analysing seven years of satellite images, the team discovered over a hundred groups of moulting penguins, located on fast ice along the coast. However, in years with less sea ice, penguins were forced onto smaller patches in increasingly large and tightly packed groups.
Between 2022 and 2024, Antarctic sea ice extent hit record lows and Antarctic fast ice also reduced dramatically. In the study region, coverage declined from a 50-year average of around 500,000 km² (an area roughly the size of Spain) to just 100,000 km² in 2023 – with only 2,000 km² of fast ice near the coast.
In these years, the sea ice broke up before the penguins had finished moulting and it is likely that many of them were unable to survive. Moulting is high-risk for penguins – they cannot feed for several weeks, and summer sea ice conditions are highly variable. If forced into the ocean before their feathers are replaced, they face exhaustion from increased energy use, hypothermia and increased risk from predators.
The missing penguins
We are already seeing the impacts. In 2025, only 25 small groups of penguins were visible in satellite images, despite more favourable sea ice conditions. Before 2022, over a hundred groups of penguins had been identified in the same region. It’s unclear whether the penguins had moved to new moulting sites or whether there is significant population decline.
For emperor penguins, which live up to 20 years and don’t breed until age three to six, adult mortality poses a greater long-term threat than breeding failure.
Dr Peter Fretwell, lead author and mapping expert at British Antarctic Survey, said: “Emperor penguins already faced a myriad of threats, and the loss of moulting sites is yet another pressure. While we don’t know for sure what happened to those penguins, we know they can find new suitable breeding sites after ice loss, so it’s possible they have established new moulting sites elsewhere.
“But it’s possible that huge numbers of penguins perished after entering the Southern Ocean before they had replaced their waterproof feathers. If this has happened, the situation for emperors as a species is even worse than we thought.”
Emperor penguins provide a window on the whole ecosystem. The sea ice supports not just penguins but seabirds and seals, and a myriad of life under the sea ice – from tiny krill to giant whales. Most of these aren’t studied on an annual basis, so emperors, which can be observed using satellite remote sensing, can be used as an indicator species, giving us a hint as to what might be happening across the ecosystem.
Journal Reference:
Fretwell, P.T., ‘Discovery of Antarctic moulting sites in satellite imagery reveals new threat to emperor penguins’, Communications Earth & Environment 7, 192 (2026). DOI: 10.1038/s43247-026-03231-6
Article Source:
Press Release/Material by British Antarctic Survey (BAS)
Featured image credit: Siggy Nowak | Pixabay
