MercoPress. South Atlantic News Agency

What was the world's largest penguin colony has lost nearly two thirds of its nests

Photo: Nicole Richters

The chinstrap penguin population on Zavodovski Island, in the South Sandwich Islands, has fallen by almost two thirds since 2011, according to a study by the British Antarctic Survey. The island, described that year as the world's largest penguin colony, has lost that title.

Researchers recorded 63% fewer occupied nests in 2025 than in 2011. That year, the same organisation estimated that some 600,000 chinstrap penguins and 90,000 macaroni penguins nested on the island. For the new study, a team sailed for 15 days to Zavodovski, a volcanic island north of the Antarctic continent administered by the United Kingdom, and used drones, aerial photography, satellite imagery and tracking devices fitted to 20 birds.

According to the study's lead, Professor Norman Ratcliffe, the cause is ocean warming. “With waters warming, the krill the chinstrap penguins eat have moved southwards. Sea-ice cover to the south and a lack of suitable islands for nesting prevents chinstraps from following the food,” he said. The researchers believe the species may now qualify as officially endangered.

The team ruled out other explanations. The island's volcano, Mount Curry, last erupted significantly in 2016, while the decline has been steady since 2011. Nor do they attribute the fall to competition for krill from humpback whales, which in turn help boost krill production.

By contrast, the macaroni penguin population increased markedly. Tracking data show they forage in warmer waters to the northeast of the island, where they are likely supplementing their diet with fish and other crustaceans. Ratcliffe described the shift as “the biggest change in community composition ever observed at a single location in Antarctica” and as “further evidence of how rapid warming is impacting unique and sensitive ecosystems”.

The world's largest penguin colony is now at Cape Adare, in the Ross Sea, more than 5,000 kilometres away on the other side of the Antarctic continent.

The study comes days after Antarctic sea ice recorded its third-lowest winter maximum since satellite measurements began this year.