A catastrophic die-off of emperor penguin chicks has been observed in the Antarctic, with up to 10,000 young birds estimated to have been killed.
The sea-ice underneath the chicks melted and broke apart before they could develop the waterproof feathers needed to swim in the ocean.
The birds most likely drowned or froze to death.
The event, in late 2022, occurred in the west of the continent in an area fronting on to the Bellingshausen Sea.
It was recorded by satellites.
Dr Peter Fretwell, from the British Antarctic Survey (BAS), said the wipeout was a harbinger of things to come.
More than 90% of emperor penguin colonies are predicted to be all but extinct by the end of the century, as the continent’s seasonal sea-ice withers in an ever-warming world.
“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 told BBC News.
“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.”