A small, fume-wreathed volcanic island in the South Atlantic has lost its claim to the biggest penguin colony on Earth. Researchers from the British Antarctic Survey reported Wednesday in the journal Current Biology that Zavodovski Island, in the South Sandwich Islands, has lost more than half a million chinstrap penguins since 2011.
A 63% drop
The team combined a drone survey from a December 2023 expedition with satellite images taken roughly every five years. They found the number of occupied chinstrap nests fell 63% between 2011 and 2025, which the British Antarctic Survey says is now the fastest chinstrap decline recorded anywhere. Science magazine reported the island's total breeding population is now estimated at about 838,000 birds, down more than 40% in 15 years.
That hands the "largest colony" title to Cape Adare in the Ross Sea, home to more than a million breeding Adélie penguins, according to Science. Zavodovski had held it since surveys in 2011 suggested its penguin numbers were stable even as chinstraps declined elsewhere.
Why scientists blame warming
The researchers worked through the possible causes one by one. The island has plenty of room to nest, krill fishing is banned in the surrounding marine protected area, and a 2016 eruption didn't change the steady downward trend, National Geographic reported. Satellite tracking of individual birds pointed instead to food: the study concludes the most likely main cause is less krill as the region warms, the same pattern seen across the Scotia Sea.
The island's other resident, the subantarctic macaroni penguin, went the opposite way. Its numbers rose 28% between 2011 and 2016 and have held steady since, making it the most common penguin on Zavodovski. The British Antarctic Survey called it the largest change in penguin community makeup ever recorded at a single site in Antarctica.
Lucas Krüger, a seabird ecologist at the Chilean Antarctic Institute who wasn't involved in the research, told Science it was "the worst-case scenario," with numbers falling faster than most people expected.
What comes next
The authors write that the declines mean chinstraps' global status on the IUCN Red List, currently Least Concern, should be considered for reclassification to Endangered.