About 10,000 emperor penguins were killed in late 2022 as the sea-ice underneath the chicks melted and broke apart, due to global warming, before they could develop the waterproof feathers needed to swim in the Antarctic ocean.
Last year, the incident took place in the west of the continent, which was recorded by satellites, in an area fronting on to the Bellingshausen Sea.
Over 90% of emperor penguin colonies are predicted to become extinct by the end of the century, with the continent’s seasonal sea-ice withering away due to global warming, reports the BBC.
The complete demise of those four colonies is described in a paper published on Thursday (24 August) in the journal Communications Earth & Environment.
After completing that research, lead author Peter Fretwell of the British Antarctic Survey (BAS) said he examined satellite images of the remainder of the continent’s 66 known emperor penguin colonies.
In 19 of them — nearly 30% — most if not all of the chicks are believed to have drowned or frozen to death when the ice that once supported them melted into the sea, he said.
“Emperors depend on sea-ice for their breeding cycle; it’s the stable platform they use to bring up their young. But if that ice is not as extensive as it should be or breaks up faster, these birds are in trouble,” he added.
“There is hope: we can cut our carbon emissions that are causing the warming. But if we don’t we will drive these iconic, beautiful birds to the verge of extinction.”
The scientists tracked five colonies in the Bellingshausen Sea sector – at Rothschild Island, Verdi Inlet, Smyley Island, Bryan Peninsula and Pfrogner Point.
Using the EU’s Sentinel-2 satellites, they were able to observe the penguins’ activity from the excrement, or guano, they left on the white sea-ice. This brown staining is visible even from space.
Adult birds jump out onto the sea-ice around March as the Southern Hemisphere winter approaches. They court, copulate, lay eggs, brood those eggs, and then feed their nestlings through the following months until it’s time for the young to make their own way in the world.
This normally occurs around December/January time, when the new birds head out into the ocean.
But the research team watched as sea-ice under emperor rookeries fragmented in November, before thousands of chicks had had time to fledge the slick feathers needed for swimming.
Four of the colonies suffered total breeding failure as a result. Only the most northerly site, at Rothschild Island, had some success.
Antarctic summer sea-ice has been on a sharp downturn since 2016, with the total area of frozen water around the continent diminishing to new record lows.
The two absolute lowest years have occurred in the past two summer seasons, in 2021/22 and in 2022/23, when the Bellingshausen was almost completely devoid of ice cover.
What is more, the slowness of floes to form in recent months means the colonies will probably not be producing chicks for at least another year.
Winter maximum sea-ice extent, normally reached in September, will track far below where it would normally be.
In the Arctic, the sea-ice has been in a decades-long, steady decline. The Antarctic in contrast seemed more robust. Up until 2016, it was becoming slightly more extensive year on year.
Studies in the Arctic have suggested that if we could reverse climate warming somehow, the sea-ice in the polar north would recover. Whether that might also apply in the Antarctic, we don’t know. But there’s every reason to think that if it got cold enough, the sea-ice would reform,” said BAS colleague Dr Caroline Holmes, who is an expert on Antarctic sea-ice.
Currently, emperors are classified as “Near Threatened” by the International Union for Conservation of Nature (IUCN), the organisation that keeps the lists of Earth’s most endangered animals.
A proposal has been made to lift emperors into the more urgent “Vulnerable” category because of the danger posed by climate warming to their way of life.