Over the past 14,000 years, Adélie penguin numbers in East Antarctica increased 135-fold because of disappearing glaciers and sea ice. The red staining is a mixture of mud and bird guano. Credit: Louise Emmerson

Antarctic glaciers and sea ice may shrink as global temperatures rise, but Adélie penguins can thrive in a less icy Antarctic landscape, a new study indicates. By determining probable population levels of the birds as far back as 22,000 years ago, the research has revealed that the numbers of East Antarctic Adélie penguins swelled in the past 14,000 years.

The birds’ abundance grew pretty much in reverse proportion to the decline of Antarctic glacial and sea ice as the Earth thawed from its last ice age. Adélie penguins live along much of Antarctica’s coast, but over the past 14,000 years, the East Antarctic population increased 135-fold, reports Jane Younger, who was at the University of Tasmania, Australia, at the time of the study, and her colleagues. The team published its findings yesterday in BMC Evolutionary Biology.

Less Ice Means More Penguins

Adélie penguins need three environmental conditions to flourish: “They need ice-free terrain for their nests, they need open water access to their beaches, and they need a consistent food supply so they can forage and return to their colonies,” said Steven Emslie, an ornithologist from the University of North Carolina, Wilmington, who was not involved in this study. East Antarctica met those conditions as glacial ice retreated inland and sea ice melted from penguin foraging grounds. But regional variability meant that Adélie penguins in other parts of Antarctica didn’t benefit from climate change in the same way.

The many-fold increase in Adélie penguin numbers in East Antarctica isn’t constrained to the past few decades when humans ramped up their rate of forcing greenhouse gases into the atmosphere. The researchers used mitochondrial DNA from 56 living penguins to retrace the birds’ demographic history for the past 22,000 years. They determined that up until about 15,000 years ago, there were fewer than 1000 East Antarctic Adélie penguins. However, as conditions improved for the penguins there, other penguins from the Scotia Arc may have migrated over and bolstered the East Antarctic population. After that, the Adélie penguin population on East Antarctica increased in line with a general deglaciation trend as the Earth emerged around that same time from its last global glaciation.

In the past 30 years, as climate change ramped up and conditions continued to improve for the penguins, the Adélie population nearly doubled. Scientists estimate the current Adélie population at around 1.14 million breeding pairs, with 30% of them coming from the East Antarctic region.

Continued Growth Is Unclear

“The warming trend does reach a threshold where it can be beneficial at first but then start having negative impacts.”

Even though the East Antarctic Adélie penguin population has grown abundantly, that doesn’t necessarily mean the population will continue to do so. Scientists don’t know how the penguin’s prey, Antarctic krill, will react to warming temperatures, and the temperatures might become too warm for the penguins themselves. “The warming trend does reach a threshold where it can be beneficial at first but then start having negative impacts,” said Emslie, who has already seen negative effects on Adélie penguins in his own research along the Antarctic Peninsula.

The new study provides rare insight into how an animal population reacts to climate change on a millennial time scale, in contrast to a more recent decadal scale. “I think it’s important to realize that the climate change that’s happening now is not a short-term kind of thing. It’s a real change in the climate that’s going to last thousands of years,” said Younger, the study’s lead author, who is now at Loyola University in Chicago, Ill.

“We need to think about not just how they’re going to be affected in the short term, but how they’re going to be affected in the long term as well.”

“If we want to really think about the effects of climate change on these animals, we need to think about not just how they’re going to be affected in the short term, but how they’re going to be affected in the long term as well. And that’s where these millennial-scale studies into the past can help.”

—Cody Sullivan, Writer Intern

Citation: Sullivan, C. (2015), Ice loss benefits Adélie penguins—For now, Eos, 96, doi:10.1029/2015EO040059. Published on 19 November 2015.

Text © 2015. The authors. CC BY-NC 3.0
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