Zavodovski Island once had the world’s largest penguin colony, but it has now seen the biggest population change ever recorded at a single Antarctic site. For many years, scientists have relied on these seabirds to show how healthy the ecosystem is.
A recent study in ‘Current Biology’ found that the chinstrap penguin population on the island has dropped by 63 percent.
In 2023, six researchers visited the remote volcanic island during the important incubation period. They used drones to take thousands of high-resolution photos of the nesting areas. The team then combined these new images with satellite pictures from 2011 to 2025 and created a special computer program to count the penguins accurately.
The software could tell the penguin species apart. It identified chinstrap penguins by their bluish color and the rings of guano around them, and it recognized macaroni penguins by their darker backs and the way they nest closer together.
The results showed a huge change in the ecosystem. From 2011 to 2025, the number of chinstrap breeding pairs dropped from about 542,000 to only 201,000. Researchers used satellite tags to track where the penguins fed and found that commercial fishing, humpback whales, and a volcanic eruption in 2016 were not the main reasons for the decline.
Instead, they found that warmer ocean temperatures and the loss of Antarctic krill were the main causes. Since chinstrap penguins mostly eat these small crustaceans, having fewer krill puts their breeding and survival at risk.
The drop in numbers is now so serious that chinstrap penguins might soon be reclassified from Least Concern to Endangered worldwide.
In contrast, the number of subantarctic macaroni penguins grew by over 28 percent between 2011 and 2016, making them the most common species on the island. Macaroni penguins eat a wide range of foods and can travel into warmer waters to find meals, which helps them adapt better as the ocean changes.
Altogether, the data showed that Zavodovski Island lost over 250,000 breeding pairs. As a result, it is no longer the world’s largest penguin colony. That title now belongs to the Adélie colony at Cape Adare in the Ross Sea.