Zavodovski Island loses title as largest penguin colony after chinstrap population drops 63%

Population collapse on Zavodovski Island

Aerial and satellite surveys conducted by the British Antarctic Survey (BAS) revealed that the chinstrap penguin population on Zavodovski Island declined by 63% between 2011 and 2025. The volcanic island, located in the South Sandwich Islands roughly 2,000 kilometres from the nearest permanent settlement, previously hosted the largest penguin colony on Earth. The number of breeding chinstraps fell from roughly 1.09 million individuals in January 2011 to 402,000 in 2025, representing a loss of more than 680,000 birds. As a result of the decline, Zavodovski has ceded its status as the largest penguin colony in the world to the Adelie penguin colony at Cape Adare in the Ross Sea, which counted over one million birds in 2018.

Norman Ratcliffe, a penguin ecologist at the British Antarctic Survey and lead author of the study published in Current Biology, described the scale of the loss.

It is an enormous population crash, equivalent to half a million breeding individuals being lost from that island.

Climate heating and krill contraction

Researchers linked the decline of the chinstrap population directly to shifts in ocean temperatures and marine food supply. Chinstrap penguins rely on a specialized diet consisting almost entirely of Antarctic krill, a small crustacean measuring between 1 and 6 centimetres. Tracking devices fitted to 20 birds showed that chinstraps forage primarily in cooler waters to the northwest of Zavodovski Island. Regional ocean warming has driven krill distributions southward into the Weddell Sea, leaving northern foraging grounds depleted. Because dense sea ice lies to the south and alternative nesting islands are lacking, the birds cannot follow the krill further south.

With waters warming, the krill have moved southwards. Sea-ice cover to the south and a lack of suitable islands for nesting prevents chinstraps from following the food.

Differing fortunes among penguin species

While chinstraps experienced substantial losses, the island population of macaroni penguins expanded over the same 14-year monitoring period. Macaroni penguins on Zavodovski increased from approximately 338,000 individuals in 2011 to 433,000 in 2025, an increase of roughly 30%. Biologists attribute this divergence to dietary flexibility, as macaroni penguins maintain a more varied diet that incorporates fish and squid alongside krill. Macaroni penguins now outnumber chinstraps on Zavodovski, bringing the total penguin population on the island to more than 835,000 individuals.

Volcanic activity and conservation status

To conduct the census on Zavodovski, a BAS team sailed for 15 days across the Southern Ocean to reach the island. Researchers deployed aerial drones, military aircraft photography, and satellite imagery to count occupied nests across the rugged volcanic terrain. The researchers evaluated whether the March 2016 eruption of Mount Curry, also known as Mount Asphyxia, contributed to the loss of birds. Field analysis showed that volcanic ash blew northeast over areas unoccupied by nesting penguins, and census data confirmed that population declines began around five years before the eruption and continued at a steady rate.

Following the documented losses across the South Sandwich Islands, which host 38% of the global chinstrap population, the study authors recommended that the International Union for Conservation of Nature redesignate the chinstrap penguin as endangered. This would replace its current classification as a species of least concern.