The world’s largest colony of King Penguins has declined by 88 percent over the last 35 years, according to a new study from French and South African researchers.
The colony, located on Île aux Cochons, a 26-square-mile island in the Crozet archipelago in the Southern Ocean, numbered 500,000 pairs of King Penguins in the early 1980s, but now its population is down to 60,000 pairs.
The findings were published in the journal Antarctic Science.
Known since the 1960s, the colony of King Penguins on the island 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.
A team from the Chizé Centre for Biological Studies 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 between 1960 and the present, the researchers studied changes in its contours over the years. They found that the colony has shrunk, yielding its territory to encroaching vegetation. Photographs taken from a helicopter during the Antarctic Circumpolar Expedition confirm that the colony’s penguin population has plummeted.
Data show that the decline began in the late 1990s, coinciding with a major climatic event in the Southern Ocean related to El Niño. 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. That is, 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 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.
While the effects of climate change may be at work, Science Alert notes that colonies on other nearby islands have remained stable or increased in size. “This leads researchers to believe that the reason for the decline is specific to Île aux Cochons, rather than global,” the site reports.
Disease is another hypothesis entertained. Avian cholera is currently ravaging populations of seabirds on other islands in the Indian Ocean, like albatrosses of Île Amsterdam and the penguins of Marion Island.
Still, none of these possibilities seems to offer a satisfactory explanation for a decline of the magnitude observed on Île aux Cochons, scientists say. Field studies should be getting under way shortly to verify initial conclusions drawn from the satellite images.
“The cause of the massive decline of the colony remains a mystery, and needs to be resolved,” the researchers wrote. “Although the decline started at least 20 years ago, it appears to be ongoing, and the causes of the decline may still be active.”
Read the abstract
Henri Weimerskirch, Fabrice Le Bouard, Peter G. Ryan, C.A. Bost. Massive decline of the world’s largest king penguin colony at Ile aux Cochons, Crozet. Antarctic Science, 2018; 30 (04): 236 DOI: 10.1017/S0954102018000226
Read our newsletter!
Sign up for our free e-newsletter to receive news, photos of birds, attracting and ID tips, and more delivered to your inbox every other week. Sign up now