A drastic fall in the size of the world’s biggest colony of king penguins has alarmed scientists – who are scrabbling for an explanation.
The colony in the southern Indian Ocean has shrunk by 88 per cent since it was last counted in the 1980s, according to a study published in the August issue of Antarctic Science.
In 1982, scientists found more than two million penguins, and 500,000 breeding pairs, on remote Ile aux Cochon. There are now thought to be only 60,000 breeding pairs.
The researchers used aerial photography and satellite images to take the new penguin census.
Ile aux Cochon, or Pig Island, is a sub-Antarctic member of the Crozet Islands and part of the French Southern and Antarctic Lands. Its isolation and inaccessibility has made monitoring the colony difficult – and the fall in numbers caught researchers by surprise.
“It is completely unexpected, and particularly significant since this colony represented nearly one-third of the king penguins in the world,” French ecologist Henri Weimerskirch, the first author on the paper, told Agence France Presse.
The scientists don’t know what has caused the dramatic fall, but likely causes range from climate change to disease and overcrowding.
One theory lays the blame on a strong El Nino in 1997, which might have warmed the ocean surrounding Ile aux Cochon enough to push away animals and fish that the penguins feed on.
“This resulted in population decline and poor breeding success” for all the king penguin colonies in the region, Dr Weimerskirch said.
There are no other islands near enough for the king penguins to swim to to find an alternative home.
In fact, in an earlier study, Dr Weimerskirch and his team found that climate change, on its current trajectory, was likely to make the the archipelago that contains Ile aux Cochon unviable for king penguins by the middle of this century.
The researchers say overcrowding might also have contributed to the decline.
“The larger the population, the fiercer the competition between individuals,” France’s National Centre for Scientific Research, which funded the study, said in a statement.
“The repercussions of lack of food are thus amplified and can trigger an unprecedented rapid and drastic drop in numbers.”
Another possibility is avian cholera, which has killed seabirds on nearby islands and has previously affected king penguins. Finally, invasive pest, such as rats, mice or cats, might have found their way onto the island.
King penguins are the second-largest penguin species after emperor penguins. They weigh about 15 kilograms and can be up to a metre tall. They’re known for the orange colouring on their upper breast, beak, neck and head.
The penguins can travel more than 400 kilometres to eat, feeding on lanternfish and squid. But they do not migrate, and will live in the same areas for years.
The team hopes to return to Ile aux Cochon in early 2019 to study the penguin colony further.