Researchers at the Chizé Center for Biological Studies (CNRS/University of La Rochelle) have observed, thanks to high-resolution satellite images, a massive 88% decline in the largest king penguin colony located on Île aux Cochons in the Îles Crozet archipelago.
The cause of the disappearance of the king penguin colony could be environmental, however, the mystery remains intact. These results hve been published in Antarctic Science.
Known since the 1960s, the colony of king penguins on Île aux Cochons, in the southern Indian Ocean, had the distinction of being the world’s biggest colony of king penguins and second biggest colony of all penguins. However, due to its isolation and inaccessibility, no new estimates of its size were made over the past decades.
How was the reduction in size measured?
The research team used high-resolution satellite images to measure changes in the size of the colony since the island was last visited by a crew of scientists in 1982. At the time, the colony included 500,000 breeding pairs and consisted of over two million penguins.
To calculate the area occupied by the colony at different times, the researchers studied changes in its contours over the years.
The researchers found that the colony has shrunk, yielding its territory to intruding vegetation. Photographs taken from a helicopter during the Antarctic Circumpolar Expedition confirm that the colony’s penguin population has plummeted.
What did the data show?
Data from the study shows that the decline in the king penguin colony began in the late 1990s, coinciding with a major climatic event in the Southern Ocean related to El Niño.
According to CNRS, this event temporarily affected the foraging capacities of another colony 100 km from Île aux Cochons, causing it to dwindle. The same process may be responsible for the fate of the Île aux Cochons colony. Its size may also subject it to density-dependent effects.
It is argued that this could be because of a larger population, as the larger the population, the fiercer the competition between individuals, slowing the growth of all members of the group. The repercussions of lack of food are therefore 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.
Another hypothesis was the idea of disease as avian cholera is currently devastating populations of seabirds on other islands in the Indian Ocean.
Still, none of these possibilities seems to offer a satisfactory explanation for a decline of the magnitude observed on Île aux Cochons.
Field studies led by CNRS researchers, with support from the French Polar Institute (IPEV), and in close partnership with TAAF nature reserve staff, should be getting under way shortly to verify initial conclusions drawn from the satellite images.