Formerly the world's largest penguin colony collapses

A remote island near Antarctica has lost its title as home to the world's largest penguin colony. New research has measured the rapid decline in the population and examined possible causes.

Zavodovski Island is located far from civilization in the South Atlantic, just over 1,500 kilometers north of Antarctica. The barren volcanic island remains ice-free for most of the year - and offers a special habitat.

The first explorers in the early 19th century reported an extraordinary smell on the island, which is known as the “smelliest island in the world”. The authors are hundreds of thousands of penguins who live there on barely 15 square kilometers. A survey in 2011 counted almost 600,000 chinstrap penguins and 90,000 golden-crested penguins.

At that time it was by far the largest penguin colony in the world. But that is changing rapidly. A study recently published in the journal “Current Biology” showed a massive decline in the population. Since 2011, the number of chinstrap penguins has fallen by two-thirds, the fastest population loss of the species in the world.

The island is more than 2,000 kilometers from the nearest permanent human settlement. Researchers from the British Arctic Survey sailed for 15 days through stormy waters to reach them. From their base camp on the rocky coast, they flew over the area with drones and used tracking devices to estimate the number of remaining penguins.

Within barely 15 years, the number of chinstrap penguins on Zavodovski Island alone fell by around 300,000 individuals. The world's largest penguin colony is now located on Cape Adare, a largely ice-free headland on the East Antarctic mainland.

The researchers tried to reconstruct the cause of the sharp decline in numbers. Tracking data has shown that the penguins prefer to forage in cooler waters northwest of the island. There they would expect Antarctic krill, which makes up the majority of their diet.

Norman Ratcliffe, who led the British Arctic Survey expedition, said in a press release: "The problem, however, is that the krill have migrated south into the Weddell Sea due to warming waters. Sea ice cover in the south, as well as the lack of suitable islands for breeding, prevent chinstrap penguins from following their food source."

The assumption is supported by another observation. In the years between 2011 and 2016, the population of golden-crested penguins, which are also resident on the island, grew by 28 percent. Since then, their number has remained at a stable level.

In contrast to chinstrap penguins, golden-crested penguins have a broader diet and can switch to alternative prey such as fish and crustaceans when krill are less common. Tracking data showed that they continued to forage primarily in warmer waters northeast of the island, where they likely supplemented their diet with these alternative food sources.

The development has a massive impact on the population of chinstrap penguins. The South Sandwich Islands, which include Zavodovski Island, are home to around 30 percent of the global population. According to the new results, this penguin species could soon be added to the Red List of Threatened Species.