Thousands of Emperor Penguins in western Antarctica lost their chicks last year, largely due to receding Sea Ice, satellite data suggest.

Over the last two years, sea ice has reached record lows around much of Antarctica (SN: 7/5/23). But while looking at satellite images in 2022, geographer Peter Fret well noticed that ice in one area was melting especially early in the year. He and his colleagues wanted to measure the impact of this ice loss — in the Bellingshausen Sea off western Antarctica — on emperor Penguins (Appetites Forster) in the region.

So the researchers looked at satellite images of colonies to determine the fate of the breeding season (SN: 8/4/20). Of the five colonies observed, four probably lost all their chicks, the team reports August 23 in Communications Earth & Environment.

Emperor penguins rely on stable sea ice throughout their breeding season, which lasts from April to January. When an egg hatches, the newborn chick must fledge, losing its downy feathers to gain its waterproof coat.

In 2022, sea ice broke up before some colonies were finished fledging. Without waterproof feathers, fledging birds were unable to survive, Fret well says. Of the youngsters from the 10,000 or so breeding pairs in the region, “we think about 850 of the chicks survived,” says Fret well, of the British Antarctic Survey in Cambridge, England.

Penguin colonies can recover from a single failed breeding season, says Annie Schmidt, a seabird ecologist at Blue Point Conservation Science in Petaluma, Calif., who wasn’t involved in the new study. And the researchers looked at only a few emperor penguin colonies of the 62 throughout Antarctica.

Some of those other colonies have also experienced bad breeding seasons lately. On Antarctica’s Brunt Ice Shelf, the world’s second-largest emperor penguin colony at the time had three years of breeding failure from 2016 to 2018 after storms broke up sea ice there, Fret well and a colleague previously reported. Between breeding failure and mass emigration to another site, the colony all but disappeared.

Repeated, or more widespread, failure could threaten colonies and, eventually, emperor penguins as a whole.

The new study, documenting breeding failure across several colonies at once, “is the first observation that’s in line with the worst expectations of what could happen” as the Earth continues to warm, Schmidt says. “I’m concerned — it’s not a good sign.” Recent estimates predict that the changing climate and melting sea ice could cut emperor penguin populations by more than half by 2100.

Only months after their first ocean swim, young emperor penguins are braving Antarctica’s treacherous winter seas. GPS trackers strapped to 15 young penguins showed the birds venturing north to warmer waters beyond Antarctica’s pack ice in December 2013, and returning a few months later as the waters chilled.

That finding surprised some scientists, who thought the inexperienced juveniles might play it safe closer to the Antarctic sea ice’s edge rather than risk freezing or drowning in the choppy open sea. After all, “they just learned how to dive a few months beforehand,” says marine ecologist Sara Larousse at the Woods Hole Oceanographic Institution in Massachusetts.

But within a few weeks of being on their own, at around 5 months old, these plucky penguins were already diving to depths of around 100 meters, like adult penguins do, the researchers report January 17 in Marine Ecology Progress Series. That’s just after they had shed their fluffy down, and before they had built up an insulating fat layer.

The tracked birds then headed more than 1,000 kilometers north to open, ice-free waters, in some cases reaching points roughly halfway between Antarctica and Australia. Data from more than 62,000 dives indicate the emperor penguins (Appetites Forster) made mostly shallow dives there, hunting fish and krill that feast on floating algae, the authors say.

In March or April, when the birds were about 8–9 months old, the fattened youngsters returned south and ventured back to Antarctica’s sea ice for winter.

Scientists don’t yet know why the penguins return to the ice, Larousse says, suggesting it could be to feed on krill that eat algae attached to the bottom of the ice. Learning more about these early behaviors helps scientists understand how lost sea ice and other changes could affect the penguins — a task that’s becoming more important amid climate change.