World's largest penguin colony hit by 'alarming' decline in numbers

Almost two-thirds of the population of chinstrap penguins have disappeared from a remote volcanic island near Antarctica, aerial surveys suggest.

Zavodovski Island was home to the largest penguin colony in the world, but researchers who carried out the surveys say it has now lost that accolade.

According to the study, there were 63% fewer occuplied nests of chinstrap penguins in 2025 than at the same time in 2011.

The research team say climate change is affecting the birds' food supply and survival, and the penguins may now be officially endangered.

Another species of penguin, the macaroni, also nests on the island and is thriving, which scientists believe is linked to their more varied diet.

Zavodovski is part of the South Sandwich Islands, a remote archipelago north of the Antarctic continent which is a UK overseas territory.

In 2011, it was hailed by the British Antarctic Survey (BAS) as home to the largest penguin colony in the world - with an estimated 600,000 chinstrap penguins and 90,000 macaroni penguins nesting on its bleak, rocky terrain.

BAS, which led this new research, says it is "one of the most extreme places in the world to undertake fieldwork".

A BAS team sailed for 15 days to reach the island and study its avian inhabitants, using drones, aerial photography and fitting tracking devices to 20 birds.

This research and satellite imagery suggested that - between 2011 and 2025 - the number of occupied chinstrap penguin nests declined by 63%.

Where did all the penguins go?

The researchers say the "alarming" fall in the chinstrap population is all about the food supply and rising ocean temperatures brought about by climate change.

Prof Norman Ratcliffe, who led the research, explained that the chinstraps' "specialist diet" and preference for cooler waters appears to have left them vulnerable.

"With waters warming, the krill [that 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.

Hungry whales and active volcanoes

The team examined other possible threats to the penguins' precarious existence on their remote island. Birds here nest in the shadow of an active volcano - Mount Curry, also aptly known as Mount Asphyxsia.

Sites downwind of the volcano have been given names including Stench Point, Noxious Bluff and Asphyxia Plain, because of the smell of fumes emitted from the crater.

Dr Ratcliffe told BBC News: "When you add all the penguin guano on top of that, and you really do have one of the smelliest places in the world.

"It's like a penguin Mordor."

Mount Curry's last major eruption was back in 2016, but the penguin declines that this study analysed have been steady and ongoing since 2011, suggesting that something else was happening.

Another concern was competition for the krill that chinstrap penguins rely on - possibly from migrating humpback whales. But, while the humpbacks eat huge quantities of krill, they also help boost krill production by fertilising marine plants that the krill feed on (with their huge quantities of whale poo).

Researchers say a more fundamental, climate-driven shift in ocean food supplies is to blame.

There is an unexpected element of this story that also adds to the picture of how - and why - this region is changing: While the chinstrap population has been declining, the number of macaroni penguins on the island has increased dramatically.

Macaroni penguins, scientists say, are more adaptable, because they have a broader, more flexible diet.

Tracking data from the study showed that the macaronis foraged in warmer waters to the northeast of the island, where scientists say they were were likely to be supplementing their diets with fish and other crustaceans.

Dr Ratcliffe said this shift was "biggest change in community composition ever observed at a single location in Antarctica".

"Our data shows that the cold-adapted Antarctic chinstrap species are no longer thriving beside their sub-Antarctic neighbours," he added.

"It is further evidence of how rapid warming in the Antarctic is impacting unique and sensitive ecosystems."

As for the title of world's largest penguin colony, scientists say that is now held by a site more than 5,000km away - on the other side of the Antarctic continent - Cape Adare in the Ross Sea.

The research is published in the journal Current Biology, external.