World’s largest penguin colony loses two-thirds of its population

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The world’s largest penguin colony on a remote island near Antarctica has suffered a sharp decline in numbers, most likely because of the climate crisis, a new study has found.

Researchers from the British Antarctic Survey found a 63 per cent drop in occupied chinstrap penguin nests between 2011 and 2025 on Zavodovski, a volcanic island in the South Sandwich Islands.

The number of breeding chinstraps fell from 1.09 million to 402,000, according to the study published on Wednesday in the journal Current Biology.

This means Zavodovski island is no longer the world’s largest penguin colony. The title now belongs to Cape Adare on the other side of Antarctica in the Ross Sea.

The South Sandwich Islands, a British overseas territory, are a remote archipelago north of Antarctica, and Zavodovski is the northernmost of them. It is twice the size of Gibraltar and lies 2,000km from the nearest permanent human settlement.

The researchers sailed for more than a fortnight to reach it, using drone surveys, aerial photography and tracking devices fitted to penguins.

For years the island appeared to buck the trend of chinstrap decline reported across Antarctica and its surrounding islands. Now, the researchers say, it is suffering the highest rate of chinstrap decline in the world.

“This is a worrying decline for chinstraps, which have specialist diets and specific ocean temperature preferences,” said Professor Norman Ratcliffe, penguin ecologist at the survey who led the study. He described the fall as “an enormous population crash”.

Chinstraps, named for the black line that runs cheek-to-cheek under the beak, feed on Antarctic krill, small shrimp-like animals that make up most of their diet.

Tracking data shows the penguins prefer to feed in cooler waters to the northwest of the island, where they would expect to find krill. “The problem is, with waters warming, the krill have moved southwards into the Weddell Sea,” Prof Ratcliffe explained.

“Sea-ice cover to the south and a lack of suitable islands for nesting prevents chinstraps from following the food.”

Macaroni penguins on the other hand saw their population increase by 28 per cent between 2011 and 2016, from about 338,000 to 433,000, and hold steady thereafter. So, they now outnumber chinstraps on the island.

Macaronis, unlike chinstraps, enjoy a more varied diet and switch to fish and other crustaceans when krill becomes scarcer. Tracking data shows them feeding mainly in warmer waters to the northeast of the island.

“Our data shows that the cold-adapted Antarctic chinstrap species are no longer thriving beside their sub-Antarctic neighbours,” Prof Ratcliffe said. “It’s the biggest change in community composition ever observed at a single location in Antarctica, which provides further evidence of how rapid warming in the Antarctic is impacting unique and sensitive ecosystems.”

He told the Guardian that the rise in the macaroni population was small comfort because all penguins would run out of space if current trends continued. “Each ecosystem could be regarded as like a giant Jenga set,” he said, “and every component that you remove increases the risk of ecosystems collapsing completely.”

The researchers tested other explanations for the decline before pointing to the climate crisis. The island’s volcano, Mount Curry, erupted in March 2016 and deposited smoke and ash over the lower slopes, but the study found the decline began earlier.

“The decline in chinstrap colony area was in progress prior to the eruption and continued at a constant rate thereafter,” the study noted. The data also showed that chinstraps avoided the area where ash and lava landed.

The researchers also ruled out competition for nesting space as an explanation because the island contained enough breeding habitat. They said krill fishing was unlikely to be a main cause because harvesting was banned in the marine protected area around the island, though they said it was unclear how fishing in connected waters was affecting the wider supply of food.

They ruled out competition from humpback whales as well. The whales do eat huge quantities of krill but also help boost their production by fertilising the marine plants they feed on.

The study, however, noted that rising competition from macaroni penguins likely made the chinstrap decline worse.

The South Sandwich islands are home to almost a third of the world’s chinstraps and the researchers say the decline here, together with falls elsewhere in Antarctica, may be enough to move the species from the category of least concern to endangered on the global list of threatened species kept by the International Union for Conservation of Nature.

Emperor penguins were declared endangered earlier this year after sea ice loss caused large population declines, according to Euronews.

Dr Peter Fretwell, a survey researcher specialising in remote sensing of penguins, said the study was further evidence of the warming climate affecting even the most remote parts of the planet.

“The South Sandwich Islands are far from any humans, home to almost a third of the world’s chinstrap penguins,” he said, “but not even they can escape the impacts of climate change.”

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