Chinstrap and macaroni penguins nesting on the volcanic slopes of Zavodovski Island (credit: Nicole Richters) A remote volcanic island near Antarctica has lost its title of largest penguin colony in the world, as new research reveals massive population declines, igniting fears for species’ survival. Researchers from British Antarctic Survey (BAS) have uncovered the loss of over half a million chinstrap penguins from the Antarctic island of Zavodovski in the South Sandwich Islands.
This loss represents over a quarter of the island’s penguins, whose numbers are made up almost entirely of chinstrap and macaroni penguins, and cedes the island’s title of world’s largest penguin colony to Cape Adare in the Ross Sea.
For years, Zavodovski Island appeared to buck the trend of widespread chinstrap declines reported across Antarctica and surrounding islands. But the new study, published in the journal Current Biology, shows Zavodovski now has the highest rate of chinstrap population decline in the world, with data showing this trend stretches back to 2011.
The steady loss of the penguins suggests the island’s volcanic eruption in March 2016, which deposited smoke and ash over the lower slopes of the volcano, is not to blame. Instead, the researchers point to climate-driven changes to the Southern Ocean that are disrupting the penguins’ food supply.
As the South Sandwich Islands are home to 30% of the world’s chinstrap population, the declines here, coupled with those seen elsewhere in Antarctica, may tip chinstrap penguins into the ‘Endangered’ category on the IUCN Red List of Threatened Species.
Zavodovski Island, which is more than 2,000 kilometers from the nearest permanent human settlement, is one of the most remote and extreme places in the world to undertake fieldwork. The BAS research team sailed for 15 days across stormy seas to reach the rugged cliffs of this volcanic island, which is around twice the size of Gibraltar. While camping on the island, they used a combination of drone surveys, aerial photography (courtesy of an RAF Atlas aircraft stationed in the Falklands), and tracking devices fitted to penguins to assess the status of the colony.
The data reveals a troubling trend. By comparing aerial surveys with satellite records, the team found a 63% decline of occupied chinstrap nests from 2011 to 2025, the cause of which can be inferred from the satellite tracking data of individual penguins.
Professor Norman Ratcliffe, BAS penguin ecologist, who led the research explains: “This is a worrying decline for chinstrap penguins, which have specialist diets and specific ocean temperature preferences. Our tracking data shows they prefer to forage in cooler waters to the northwest of the island, where they would expect to find Antarctic krill – the prey that make up the bulk of their diet. The problem is, with waters warming, the krill have moved southwards into the Weddell Sea. Sea-ice cover to the south and a lack of suitable islands for nesting prevents chinstraps from following the food.”
A changing island. Interestingly, while the chinstrap population had been declining, the population of macaroni penguins on the island increased – by 28% from 2011 to 2016, where it has remained stable since. This too, the researchers attribute to the penguins’ dining habits.
Unlike chinstraps, macaroni penguins have a broader diet and can switch to alternative prey such as fish and crustaceans when krill become less abundant. Tracking data showed them predominantly foraging in warmer waters northeast of the island, where they were likely supplementing their diets with these alternate food sources.
According to Professor Ratcliffe, the decline of chinstraps, and population growth of macaroni penguins, represent an altogether more concerning change: “Our data shows that the cold-adapted Antarctic chinstrap species are no longer thriving beside their sub-Antarctic neighbors. It is 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.”
The researchers ruled out other explanations for the change, such as competition for nesting space between the two penguin species, or krill fisheries in the region. This is largely due to the availability of breeding habitat on the island, and the ban of krill harvesting in the Marine Protected Area (MPA) surrounding the island. However, it is unclear how krill fishing in areas connected by currents to this MPA may be affecting wider food availability.
An uncertain future The researchers are concerned that such large changes to the chinstrap and macaroni populations could cause wider disruption to marine food webs in the region. But it’s the state of our ecosystems in a changing world that concerns them the most.
Peter Fretwell, a BAS researcher who specializes in remote sensing of penguins, puts it plainly: “Our study is another example of a warming climate impacting even the most remote parts of our planet. The South Sandwich Islands are far from any humans, home to almost a third of the world’s chinstrap penguins – but not even they can escape the impacts of climate change.”
The news comes just six months after Emperor penguins were declared an endangered species due to sea ice loss triggering massive population declines in Antarctica, casting a bleak shadow over the future of our iconic seabirds.
Population declines and changes in community composition at the world’s largest penguin colony by Ratcliffe et al., is published in the journal Current Biology on Wednesday 7 October at 16:00 BST