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After three decades out of the public eye, a giant colony of king penguins has lost 90 percent of its population, according to a new study.
The colony of 500,000 breeding pairs, long considered the largest of king penguins in the world, lived on the Île aux Cochons (or, less elegantly, Pig Island), a French territory in the Crozet archipelago in the southern Indian Ocean between South Africa and Antarctica.
But the penguins haven’t been counted in person since 1982 when researchers last visited. In late 2016, researchers flew over it by helicopter and saw noticeably fewer penguins than expected.
Since then, by closely examining three decades of satellite images, researchers have concluded that there are just 60,000 breeding pairs left on the island.
“It was really a surprise for us,” said Henri Weimerskirch, a co-author on the new paper, published in Antarctic Science, and a member of the research teams in 1982 and 2016. “It’s really very depressing.”
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The research team suspects that climate change could be playing a role, as it has with other colonies of penguins in parts of Antarctica. But competition for resources, diseases and relocation may possibly have contributed to population losses.
Researchers plan to do a head count on the island but they can’t get there until late fall 2019 at the earliest, because of the cost and timing issues, said Dr. Weimerskirch, research director of the Chizé Centre for Biological Studies at the French National Centre for Scientific Research. A protected nature preserve, Pig Island isn’t easy to reach, and the animals can’t be seen from the water, because the colony is situated inland, he said.
If the count from the satellite images proves accurate, it would significantly reduce the global population of king penguins, estimated at 1.5 million to 1.7 million breeding pairs worldwide with this loss. They had not been considered endangered before, but might be, Dr. Weimerskirch said.
King penguins are second-largest in population after emperor penguins. They don’t nest, but lay one egg and parents take turns incubating the egg with an abdominal layer called a brood patch for two months. King penguins leave their young and swim south to forage for fish and squid in the waters of the Antarctic polar front, where cold, deep water mixes with more temperate seas. If they can’t reach this polar front and can’t swim back within about a week, their chicks will starve to death.
The trouble seems to have started in 1997 when an El Niño weather event drove up temperatures considerably for a year, pushing their food sources so far south that the chicks died before their parents could return to feed them.
All the king penguin colonies in the South Indian Ocean suffered that year, but populations on nearby Possession Island quickly rebounded, counts there showed, so researchers assumed that the colony had rebounded on Pig Island as well, Dr. Weimerskirch said. The satellite images show they did not.
It’s not clear why the colony did not recover. Dr. Weimerskirch said the possibilities include some kind of infection or parasite affecting only animals on this island; predators like feral cats devastating nests; or, perhaps there was so much competition for resources in the giant colony that only the hardiest creatures could survive.
Some of the animals may have relocated from Pig Island, which is about 26 square miles (about the size of Manhattan), Dr. Weimerskirch said.
He said the team spotted a small colony on a nearby island that didn’t exist in the 1980s. But it only includes a few tens of thousands of breeding pairs — not anywhere near as many as were lost — and relocation isn’t easy for the penguins, which naturally return to where they were born.
Emiliano Trucchi, an evolutionary biologist at the University of Ferrara in Italy, who also studies king penguins in the Crozet archipelago, said he was disturbed by the report.
Work that Dr. Trucchi and his colleagues published earlier this year raised questions about how king penguins would cope with warming seas from climate change. His model predicted the Crozet penguins would lose their habitat by 2100 and be forced to relocate or die.
A local problem like what is happening on Pig Island could hasten their decline, Dr. Trucchi said.
“It deserves further investigations,” he said. “It’s a very peculiar process and we need to understand how to fit this into the big picture.”