The world’s largest king penguin colony has suffered a “mystery” decline from around 500,000 breeding pairs to 60,000, researchers say.
The “massive, unexpected” fall has seen numbers dwindle 88% on Ile aux Cochons, located in the Indian Ocean, in 35 years.
Experts say the population’s decimation is “a mystery, and needs to be resolved”.
King penguins are the second-largest penguin species at around 90cm tall, only surpassed in size by the emperor penguin.
Aerial photographs and satellite images were used to estimate the size of the colony, as there had been no analysis for decades and the last visit to the island was in 1982.
French researchers from the Centre for Biological Studies in Chize say numbers started to fall from the late 1990s and that the decline “appears to be ongoing”.
Ile aux Cochons – located in the remote Crozet archipelago between South Africa and Antarctica – was once thought to be home to the second-largest colony of any species of penguin.
But experts pored over helicopter photographs to estimate that 502,400 breeding pairs in 1982 had fallen to 59,200 in 2017, according to latest satellite images.
A single catastrophic event, such as a tsunami or volcanic eruption, is thought unlikely.
Experts say the penguins may have developed problems foraging for food, or that feral cats and mice could have started hunting chicks. Disease and parasites could also be to blame.
Despite the mysterious problems on Ile aux Cochons, in other areas penguins are thriving.
A massive colony of 1.5 million Adelie penguins was recently discovered on the Danger Islands, near South America, where scientists had previously thought numbers were in decline.