- In 1982, researchers estimated that there were more than 500,000 breeding pairs and over 2 million king penguins on the remote Île aux Cochons, or Pig Island, a French territory in southern Indian Ocean.
- More than three decades later, by 2017, the number of king penguins on the island had dropped drastically to just about 200,000 penguins, including some 60,000 breeding pairs, researchers report in a new study.
- The reasons for this decline are still unknown, but the researchers hope that further field studies will be able to verify the massive drop and identify the factors that led to it.
The world’s largest colony of king penguins has declined drastically by nearly 90 percent, a new study has found.
The massive king penguin (Aptenodytes patagonicus) colony on the remote island of Île aux Cochons or Pig Island, a French territory in the southern Indian Ocean, was first discovered and photographed in the early 1960s by a team of cartographers. In 1982, researchers used satellite images to come up with an estimate of more than 2 million king penguins on the island, including more than 500,000 breeding pairs. This made it the largest colony of king penguins on Earth, and the second largest colony of all penguins. (A colony of chinstrap penguins on the British-administered Zavodovski Island, in the southern Atlantic, has some 1 million breeding pairs.)
More than three decades later, by 2017, the number of king penguins on Île aux Cochons had shrunk to just about 200,000 penguins, including some 60,000 breeding pairs, researchers report in the study published in Antarctic Science. By analyzing satellite images of the area and data from helicopter surveys, researchers also found that the total surface area of the island occupied by the penguins has progressively declined since 1982.
“It is completely unexpected, and particularly significant since this colony represented nearly one third of the king penguins in the world,” Henri Weimerskirch, the lead author of the study and an ecologist at the National Center for Scientific Research (or CNRS) in Chizé, France, who was also part of the 1982 research team, told AFP.
Why such a massive colony has shrunk is still a mystery. However, the researchers have put forward some possible causes for the decline.
According to the team’s data, the decline in penguin numbers on Île aux Cochons started in the late 1990s, coinciding with an El Niño-like climatic event in the southern Indian Ocean that raised sea temperatures. In a previous study, Weimerskirch and his colleagues found that during this period, another penguin colony some 100 kilometers (62 miles) from Île aux Cochons had to swim farther and dive deeper for fish and squid. Since the penguins had to go beyond their normal foraging range, both chicks and adult penguins suffered.
The 1997 event may have affected the population of Île aux Cochons more severely than other colonies, the authors write in the study.
“The larger the population, the fiercer the competition between individuals, slowing the growth of all members of the group,” CNRS said in a press release. “The repercussions of lack of food are thus amplified and can trigger an unprecedented rapid and drastic drop in numbers, especially following a climatic event like the one at the end of the 1990s.”
Feral cats (Felis catus) and house mice (Mus musculus) introduced to the island could also be preying on penguin chicks and leading to the population decline, the authors write, but neither species is currently known to be a predator of king penguin chicks. Diseases like avian cholera could also be affecting the seabirds. But again, there are no data available about the occurrence of any such diseases on Île aux Cochons, the authors say.
The researchers say they hope further field studies will be able to verify the massive decline in penguin numbers, and identify the causes that may have led to it.
“Île aux Cochons is rarely visited, and the use of satellite images has allowed the detection of this unexpected phenomenon,” they write. “However, to be able to understand the cause of the decline, it is necessary to study the colony on land and at sea.”
The king penguin is the second-largest species of penguin in the world after the emperor penguin (Aptenodytes forsteri). It is currently listed as being of least concern on the IUCN Red List. The latest population data could, however, prompt a re-evaluation of the penguin’s conservation status.
Weimerskirch, H., Le Bouard, F., Ryan, P. G., & Bost, C. A. (2018). Massive decline of the world’s largest king penguin colony at Ile aux Cochons, Crozet. Antarctic Science, 30(4), 236-242. doi:10.1017/S0954102018000226.