The world’s biggest colony of king penguins has shrunk by almost 90% since the 1980s, scientists have discovered.
Experts are still trying to understand what decimated the penguin population on Ile aux Cochons (Pig Island) in the South Indian Ocean, once home to more than two million of the charismatic birds.
Leading theories include the impact of an El Nino climatic event, an outbreak of avian cholera, introduced predators such as cats, and simple overcrowding. But none of these explanations seems able to account for the size of the crash.
It was last visited by a team of scientists in 1982, when a large section of the island was carpeted by vast numbers of king penguins, which stand about three foot tall.
At that time, the colony included 500,000 breeding pairs and more than two million penguins. It was known as the largest king penguin colony in the world and the second largest of all penguin colonies.
Between 1982 and 2017 the colony collapsed in size by 88% to just 60,000 pairs and around 200,000 birds.
The shocking extent of the population decline, described as “massive” and “unexpected” by the French researchers, was revealed in satellite images and aerial photographs taken from a helicopter.
The team led by Dr Henri Weimerskirch, from the Centre for Biological Studies in Chize, France, wrote in the journal Antarctic Science: “The cause of the massive decline of the colony remains a mystery, and needs to be resolved.
“Although the decline started at least 20 years ago, it appears to be on-going, and the causes of the decline may still be active.
“Ile aux Cochons is rarely visited, and the use of satellite images has allowed the detection of this unexpected phenomenon. However, to be able to understand the cause of the decline, it is necessary to study the colony on land and sea.”
The images show vegetation encroaching onto areas that were previously occupied by penguins.
The fall in population began in the late 1990s and coincided with a major El Nino event that warmed the Southern Indian Ocean.
This may have pushed the fish and squid on which the penguins feed beyond their foraging range, said the scientists.
They ruled out a catastrophic event such as a volcanic eruption or tsunami, pointing out that the colony was well inland and the population decline was gradual.
Louisa Casson, from the environmental group Greenpeace UK’s Protect the Antarctic campaign, said: “Like so much marine life, penguins are under acute pressure from climate change, industrial fishing and pollution. While the precise cause of this colony collapse is unclear, it is a stark and sad reminder of the threats facing our oceans and their wildlife. “