Thousands of emperor penguin chicks drowned when the sea-ice on which they were being raised was destroyed in severe weather.
The catastrophe occurred in 2016 in Antarctica’s Weddell Sea.
Scientists say the colony at the edge of the Brunt Ice Shelf has collapsed with adult birds showing no sign of trying to re-establish the population.
And it would probably be pointless for them to try as a giant iceberg is about to disrupt the site.
The dramatic loss of the young emperor birds is reported by a team from the British Antarctic Survey (BAS).
Drs Peter Fretwell and Phil Trathan noticed the disappearance of the so-called Halley Bay colony in satellite pictures.
It is possible even from 800km up to spot the animals’ excrement, or guano, on the white ice and then to estimate the likely size of any gathering.
But the Brunt population, which had sustained an average of 14,000 to 25,000 breeding pairs for several decades (5-9% of the global population), essentially disappeared overnight.
Emperors are the tallest and heaviest of the penguin species and need reliable patches of sea-ice on which to breed, and this icy platform must persist from April, when the birds arrive, until December, when their chicks fledge.
If the sea-ice breaks up too early, the young birds will not have the right feathers to start swimming.
This appears to have been what happened in 2016.
Strong winds hollowed out the sea-ice that had stuck hard to the side of the thicker Brunt shelf in its creeks, and never properly reformed. Not in 2017, nor in 2018.
Dr Fretwell said: “The sea-ice that’s formed since 2016 hasn’t been as strong. Storm events that occur in October and November will now blow it out early. So there’s been some sort of regime change. Sea-ice that was previously stable and reliable is now just untenable.”
The BAS team believes many adults have either avoided breeding in these later years or moved to new breeding sites across the Weddell Sea. A colony some 50km away, close to the Dawson-Lambton Glacier, has seen a big rise in its numbers.