Zavodovski loses more than half its chinstrap penguins, survey finds

Zavodovski Island no longer holds the largest penguin colony on earth. A British Antarctic Survey study published in Current Biology counts 402,000 breeding chinstrap penguins there in 2025, down from 1.09 million in January 2011. That is a loss of more than 680,000 birds, about 63 percent, or roughly 7 percent a year. Lead author Norman Ratcliffe attributes the fall to food, not to the eruption that hit the island in 2016.

Chinstraps eat Antarctic krill. Ratcliffe's account is that warming water has pushed krill south, toward colder seas the birds do not use in the same way. The decline was already under way before the 2016 eruption and continued in a roughly straight line after it, which is why the survey treats the volcano as a secondary event. South Sandwich Islands as a group hold about 38 percent of the world's chinstraps. The 2011 surveys had found those populations stable. The new count breaks that picture on the largest island in the chain.

The other penguin on the same rock

Macaroni penguins on Zavodovski moved the other way. The study counts 338,000 in 2011 and 433,000 in 2025. Chinstraps and macaronis together still number more than 835,000 on the island. The title that moved is the single-colony record, which Zavodovski held on the strength of its chinstraps. Adélie penguins at Cape Adare, on the opposite side of the continent, now hold the largest colony, at more than one million birds on a 2018 count.

The split between the two species is the detail a short headline drops. A visitor counting birds on the ash slopes would still see a huge colony. The composition has changed. Chinstraps, tied tightly to krill, have fallen. Macaronis, with a broader diet, have risen. The net is still a large loss, because the chinstrap number in 2011 was three times the macaroni number.

How the count was made, and what it cannot say

The comparison runs from a 2011 survey to a 2025 survey, with the paper in Current Biology. Ratcliffe is named as lead author by the British Antarctic Survey. France 24's account of the release gives the two headline figures, 1.09 million and 402,000, and the macaroni pair, 338,000 and 433,000. A fourteen-year gap between full counts means the 7 percent annual rate is an average, not a year-by-year series. A bad breeding season and a real fall in adults can look the same in a single snapshot. The paper's claim is that the line was steady enough, including through the eruption, to treat the loss as a trend.

Krill is the mechanism on offer. Warming surface water in the Scotia Sea has been measured for years, and krill distributions have shifted. The study's step is to tie that shift to a named colony with a before-and-after count. It does not claim every chinstrap colony has fallen at the same rate. It claims this one has, and that this one was the largest.

What the title change is worth

Cape Adare taking the record is a bookkeeping result of the Zavodovski loss, using a 2018 Adélie figure. If Adélie numbers at Cape Adare have also moved since 2018, the ranking could change again. The durable number is the chinstrap count on Zavodovski: 402,000 breeding birds where there were 1.09 million. That is the figure fisheries managers and the Commission for the Conservation of Antarctic Marine Living Resources will read against krill catch limits in the South Atlantic. The birds and the fishery draw on the same stock.