In 2016, scientists made a gruesome discovery on East Antarctica's Long Peninsula. Hundreds of mummified Adélie penguin bodies—most of them chicks—lying at the sites of abandoned colonies. As Laura Geggel reports for Live Science, recent analysis of some of the carcasses has revealed that the penguins died hundreds of years ago. The climactic forces that killed them, however, could threaten penguin colonies today.
A team of researchers led by Zhouqing Xie and Liguang Sun of the University of Science and Technology of China performed carbon dating on tissue from 14 of the mummified penguins, reports Nature. They found that the animals died during two mass mortality events: one around 750 years ago and the other around 200 years ago.
The researchers also studied the sediment around the penguins, landscape features, geochemical data from lake sediment cores, and ice core accumulation records. In a study published in the Journal of Geophysical Research, the team concludes that the die-offs were caused by “extreme climatic anomalies,” which led to several decades of unusually heavy rains and snow.
"It is quite likely that global climate warming caused enhanced precipitation, which led to the tragedy," Sun tells Geggel.
Though adult Adélie penguins thrive in the water, excessively wet conditions can be perilous to chicks that have yet to develop waterproof plumage. If these downy little critters are exposed to too much rain or snow, they can suffer from hypothermia, which causes slow growth and death. Snow accumulation can also make it difficult for adult penguins to find pebbles for their nests, and melting snow can drown penguin eggs.
Adélie penguins are found across the Antarctic coast, and unlike many other penguin species, they are not considered threatened; the IUCN Red List ranks them as being of “least concern” on its scale of conservation needs. But in recent years, with global temperatures once again creeping upward, climatic fluctuations have put Adélie penguins in danger.
A 2016 study, for instance, predicted that one-third of Adélie penguin colonies could be in decline by 2060. And last year, scientists were shocked to discover that in a colony of around 18,000 breeding pairs on Antarctica’s Petrels Island, only two Adélie chicks survived a recent breeding season. The catastrophic failure was ascribed to a heavy rainfall and the 2010 breakup of the Mertz glacier, which caused an unusual amount of sea ice to form around the colony, making it more difficult for the penguins to find food.
“The Mertz glacier impact on the region sets the scene in 2010 and when unusual meteorological events, driven by large climatic variations, hit in some years this leads to massive failures,” Yan Ropert-Coudert of France’s National Centre for Scientific Research told Michael Slezak of the Guardian at the time. “In other words, there may still be years when the breeding will be okay, or even good for this colony, but the scene is set for massive impacts to hit on a more or less regular basis.”
Sun echoed this sentiment in his interview with Geggel of Live Science, noting that "it is believed that the current global warming trend will continue or even worsen” due to human pressures. Sun adds that if the Antarctic experiences heavy rains and snows like the ones that led to die-offs on Long Peninsula hundreds of years ago, today’s Adélie penguins faced increased chances of "massive death."