What happened

Zavodovski Island, a volcanic island near Antarctica, once held the world’s largest penguin colony. A new study published in Current Biology found a major change there between 2011 and 2025. The number of breeding pairs of chinstrap penguins, the main species counted there, fell from about 542,000 to about 201,000. A breeding pair means two adults raising chicks. That is a decline of nearly 63 percent. Across the island, more than 250,000 breeding pairs were lost. The title now belongs to the Adélie penguin colony at Cape Adare in the Ross Sea. Current Biology paper

How the change was measured

Researchers visited the island in 2023 during the penguins’ incubation period. A drone photographed almost the whole island. The team collected thousands of overlapping, high-resolution images. They compared those images with satellite images taken at intervals from 2011 to 2025. Manually counting so many birds would be difficult. So, the researchers built a computer program to process the images. It could distinguish chinstraps from macaroni penguins, the island’s other major penguin species. The team also placed satellite tags on breeding penguins. These tags showed where the birds searched for food.

What the study points to

The researchers identify regional ocean warming as the most likely main cause. Warmer water has probably reduced the supply of Antarctic krill. Chinstrap penguins depend almost entirely on krill. That makes them vulnerable when krill become harder to find.

Macaroni penguins increased and became the island’s most abundant penguin. They eat a wider range of food. They can also travel into warmer currents. This flexibility may help explain why they did better.

The team found no evidence that the island’s 2016 volcanic eruption was the primary cause. It also found no evidence that krill fishing, macaroni penguins, or humpback whales were the primary cause. These findings do not prove that every other factor had no effect. They show which explanation best fits the evidence.

Why it matters

This is more than a change in a record book. It is a large change in the animal community at one Antarctic site. One penguin species fell sharply. Another became more common. The study describes it as the largest recorded shift in penguin community composition at one Antarctic location.

Zavodovski is far from cities and people. Its changes therefore show how ocean conditions can affect wildlife even in remote places. Scientists also use penguin populations as signs of wider ecosystem health. Penguins depend on fish and krill. A change in penguin numbers can point to a change lower in the food web.

What is confirmed, and what is not

The population decline and the change in which species is most abundant are supported by repeated images and tracking data. The connection to warmer seas and fewer krill is the researchers’ strongest explanation. It is still an inference, not a direct experiment.

The study says chinstrap penguins may need a new global conservation assessment. Their current category from the International Union for Conservation of Nature is Least Concern. A move to Endangered is being considered, but it is not a final decision. The data from one island also cannot show that every chinstrap population is declining at the same rate.

What to watch next

Future surveys will need to track penguin numbers, ocean temperature, and krill availability together. Researchers will also need to see whether macaroni penguins continue to increase. The key question is whether Zavodovski’s change is local or part of a wider transformation around Antarctica.