When Sea Ice Retreated, Some Emperor Penguins Didn’t Breed

Four out of five emperor penguin colonies in Antarctica’s Bellingshausen Sea region very likely lost their chicks late last year because of disappearing sea ice underneath their breeding grounds, according to a new study.

Parts of this coastal region had lost all of their sea ice by November, which was probably before penguin chicks had grown waterproof adult feathers and learned to swim. It’s the first time scientists have seen a widespread failure across multiple penguin colonies in a region, researchers said.

“At the moment, we’re not sure if this is just a blip,” said Norman Ratcliffe, a seabird ecologist with the British Antarctic Survey and one of the authors of the new study. “But if this becomes a consistent phenomena in the longer term, clearly it’s going to have repercussions for the species.”

Sea ice levels around Antarctica in 2023 are likely to reach record low levels by a wide margin. This sudden drop has alarmed scientists and has some speculating that Antarctic sea ice is entering a new, unstable state.

“Events like this may become more common in the future,” Dr. Ratcliffe said, referring to the early loss of sea ice and penguins’ subsequent breeding failures. “So we may be looking at a harbinger of a future Antarctica.”

The Bellingshausen Sea region of Antarctica is extremely remote, so the researchers observed the penguin colonies using satellite images to track their excrement, called guano, which leaves a distinct reddish-brown trace on the snow and ice.

Emperor penguins depend on sea ice stuck to the edge of the Antarctic continent as a habitat to lay eggs and raise their young until they can swim and fend for themselves.

After remaining stable and even increasing for many years despite climate change, Antarctic sea ice began to decline around 2016. The extent of sea ice around the continent hit a record low in 2022. The Bellingshausen Sea, the area along the west side of the Antarctic Peninsula where the five penguin colonies were located, was the worst-affected region last year.

Emperor penguins sometimes pick new breeding grounds when previous sites have failed, and some have joined other colonies. But scientists have only seen them move short distances, and as more and more sea ice melts, whole regions of the coast may become inhospitable.

Scientists estimate there are currently around 600,000 emperor penguins in the wild, across 61 known colonies. In 2022, the United States listed the species as threatened under the Endangered Species Act. Although these penguins don’t live in the United States, the listing encourages international cooperation to protect the animals and requires the government to consider them when evaluating federal projects that emit greenhouse gases.

Besides human-caused climate change, the past three years’ natural La Niña climate phenomenon in the Pacific Ocean likely contributed to the Bellingshausen Sea having especially little sea ice. A flip to El Niño conditions this year could help that particular region.

The continent is just beginning to emerge from its long polar night, when emperor penguin colonies aren’t visible in the darkness to satellites. As they become visible again, the British Antarctic Survey and researchers from other countries are continuing to monitor each colony. They expect newer satellites — which are starting to track the penguins rather than just their guano — to help improve estimates of populations.

While the latest study, published on Thursday in the journal Communications Earth & Environment, focused on the Bellingshausen Sea, Dr. Ratcliffe said that the breeding failure rates last year were higher than expected all around Antarctica.

Annie Schmidt, an ecologist and Antarctica program director at the consultancy Point Blue Conservation Science, said this study yielded an important observation of regionwide breeding failure. Dr. Schmidt was not involved in this research, but has studied emperor penguin colonies.

“It’s a first warning that this is starting to happen,” she said.

Previous research has suggested that if human-caused climate change continues at its currently projected pace and the planet warms by 2.6 degrees Celsius by 2100 compared with preindustrial levels, emperor penguins could lose nearly 90 percent of their population and be on the verge of extinction. But if countries achieve the international Paris Agreement goals of limiting global warming to under 2 degrees Celsius, emperor penguins will fare much better. They may still lose 30 to 40 percent of their numbers, but scientists believe the population could eventually stabilize and survive.