Satellites Reveal New Climate Threat to Emperor Penguins

Each year for millennia, emperor penguins have molted on coastal sea ice that remained stable until late summer—a haven during a span of several weeks when it’s dangerous for the mostly aquatic birds to enter the ocean to feed because they are regrowing their waterproof feathers.

But as overall Antarctic sea ice extent dwindled to record lows in recent years, some of the frozen penguin platforms melted earlier than ever, forcing the weakened birds into smaller areas and possibly to a premature death in the icy ocean, according to British Antarctic Survey geographer Peter Fretwell, who helped pioneer counting emperor penguins from space.

“The sea ice wasn’t just breaking up into floes. In some years, it just disintegrated,” said Fretwell, author of a paper published Wednesday that matched the fate of the molting penguins against the ice records for seven years.

“If they go into the water half-moulted, they’re really in trouble because they just aren’t very strong,” he said, adding that the birds lose up to half their body weight during molt. If they enter the water before they’re ready, they can get hypothermia and become easy prey for leopard seals.

The United States listed emperor penguins as an endangered species in 2022 because multiple studies project large population losses, to near-extinction, this century under continued warming. About a quarter-million breeding pairs remain worldwide, scattered among colonies ringing Antarctica. 

The study is the first to map emperor penguin moulting sites from satellite images. It shows that a major moulting refuge along the Marie Byrd Land coast of West Antarctica has shrunk dramatically during recent record-low sea-ice years, potentially a major new threat to a species that is losing habitat to climate change at different life stages, he said.

The remote section of West Antarctica where he studied the penguins has lost more sea ice than anywhere else. Until a few years ago, researchers rarely reached the coast, which is why there are no research stations in the region. But now, in some years, almost all of it melts in summer.

“Nobody predicted it,” he said, describing the meltdown as a sudden re-adjustment after warmer ocean water thinned the ice from below, and worked its way near the surface until “the sea ice basically went,” he said.

Previous research by Fretwell and others has already suggested that climate-driven ice loss is disrupting breeding by penguins and other seabirds. The new analysis suggests that climate-driven ice loss may also be affecting adult molting, potentially exposing large portions of the global emperor penguin population to a new mortality risk.

This life stage is critical because it is the only period when adults are unable to enter the ocean safely to feed. And emperor penguins don’t reproduce prolifically, so adults must survive for years to sustain populations. 

Very Little Good News for Penguins

If adult survival is threatened, population declines can accelerate, said Rose Foster-Dyer, a marine ecologist at the University of Canterbury in New Zealand, who researches emperor penguin global population trends. 

Foster-Dyer said the Marie Byrd Land sector has long been a predictable moulting stronghold because of its persistent summer sea ice, meaning its recent decline could force birds to shift habitats, if suitable ice remains.

“There has been very little good news for emperor penguins recently, and they appear to be under great pressure through the changes to their sea ice environment,” she said. Ship-based surveys over many years suggest that penguins have historically chosen areas with high sea ice concentrations as their redoubts for molting. “If the sea ice becomes less reliable,” she said, “the birds will need to adapt and change their behaviours to survive.”

Over the past three million years, emperor penguins have survived by adapting to huge sea ice variations, but they need somewhere to go, as well as time to adapt. That process typically unfolds over millennia during slow planetary climate cycles.

But the speed of human-caused warming is a new and different shock to Earth’s climate and to emperor penguins, Fretwell said.

“They’re probably the slowest-adapting bird species genetically, and unless they’ve got it in the locker already, they’re not going to adapt.”

That means if emperor penguins don’t already have the biological capacity to adapt to swift sea ice loss, they are unlikely to evolve fast enough now.

It’s still not certain what happened to the penguins on the coast of Marie Byrd Land, and Fretwell said he hopes that at least some of them were able to find new moulting areas. 

But he’s been in touch with another group of researchers counting emperors at breeding sites, and he’s afraid their new data from the latest census will confirm the bad news.

Fretwell said 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,” he said, “the situation for emperors as a species is even worse than we thought.”