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FLICKR, CHRISTOPHER MICHEL

n emperor penguin population in Antarctica’s Weddell Sea that used to be tens of thousands of birds strong is on the brink of collapse, according to a study published today (April 25) in Antarctic Science. Satellite images of the area show that, while the colony consisted of up to 25,000 animals prior to 2016, in the last three years those numbers have dropped to almost zero.

“We’ve never seen a breeding failure on a scale like this in 60 years,” study author Phil Trathan, head of conservation biology at the British Antarctic Survey, tells the Associated Press. “It’s unusual to have a complete breeding failure in such a big colony.”

“Since we know little about the population trends of emperor penguins in most colonies, this is not good news,” Dee Boersma, a penguin ecologist at the University of Washington in Seattle who was not involved in the research, tells Science.

The decline of the so-called Halley Bay colony stems in large part from the loss of large numbers of emperor penguin chicks, which drowned in 2016 after the sea ice they’d been living on was destroyed in a storm. “The sea-ice that’s formed since 2016 hasn’t been as strong,” study author Peter Fretwell of the British Antarctic Survey in Cambridge tells the BBC.

The lack of reproduction since the catastrophe is “unprecedented,” Fretwell and Tranthan report. Many of the colony’s adults have made the 55-kilometer trek to an adjacent colony, whose numbers have grown 10-fold as it has received the migrants.

The loss of the Halley Bay colony is concerning, as researchers didn’t expect such dramatic sea ice declines to occur in this area of the Antarctic. “I thought the Weddell Sea would be one of the last places we would see this,” Tranthan tells Science. “The fact that these penguins are still vulnerable is a surprise.”