The colony of king penguins on Pig Island in the sub-Antarctic archipelago of Crozet, considered the largest in the world, has diminished by nearly 90% in 35 years, say a group of researchers, basing their estimates on images taken by satellite.
Between the early 1980s and today, “the colony has declined by 88%, from about 500,000 breeding pairs to 60,000 pairs,” according to a study published in Antarctic Science. Since it is estimated that one breeding pair represents four individuals – the couple and two youngsters – this means that there would be about 240,000 king penguins on the island.
“This is a huge reduction,” said Friday Henri Weimerskirch, a researcher at the National Center for Scientific Research (CNRS) in France, and the first author of the study published this week. “While the causes of the disappearance of these penguins could be environmental, the mystery remains,” say the researcher.
Known since the 1960s, this colony is located in the French Southern Territories (TAAF) nature reserve. In the 1980s, it was considered the largest colony of king penguins in the world. But because of its isolation and inaccessibility, this colony had not been evaluated for decades.
The king penguin (Aptenodytes patagonicus) has a white belly, a black beak and an orange patch on the side of the head. He is a little smaller than the emperor penguin.
Researchers from the Chizé Center for Biological Studies in France used high-resolution images taken by satellite to measure changes in the colony’s size since the last visit of the island by a scientific team in 1982 . At the time, the colony had 500,000 breeding pairs, a population of over two million.
To evaluate the areas occupied by the penguins from 1960 to today, the scientists measured the edges of the colony on satellite images year after year and realized that it was decreasing in favor of a return of vegetation. Snapshots taken from a helicopter during the Antarctic Circumpolar Expedition (ACE) in 2016 confirmed the dramatic reduction of the colony.
The results indicate that the decline began in the late 1990s. “The trigger” was probably a major climatic event in the Southern Ocean related to the El Niño phenomenon in 1997. This would have temporarily affected the foraging abilities of king penguins, as was observed on one colony in another island in the Crozet Archipelago and the Kerguelen Islands. “But these settlements then stabilized […] while that of the pig island has continued to decline,” says the scientist.
” It’s amazing. Something more happened on this island. You have to go there to understand,” he adds.
Several factors may have played a role: a very high density makes competition harder between individuals, especially when food is lacking, which can accentuate the decline of their population. Another hypothesis advanced: the penguins could be suffering from a disease, such as bird cholera.
“Until this study, throughout the Southern Ocean, the population of king penguins was estimated at 1.5 million breeding pairs. “This bad news coming from Pig Island means that we lost a third of the global population of king penguins,” says the researcher.