Researchers blame too much summer sea ice for causing a downward spiral in one colony

An Adélie penguin Courtesy of Kate Kloza / Australian Antarctic Program

Adélie penguins in East Antarctica may be in serious trouble: A population of the small black-and-white birds has shrunk by 43 percent over the last decade, according to new research.

Ecologists believe changing environmental conditions—not direct human activity—may be to blame for the declining numbers of Adélie penguins near the region’s Mawson research station. They shared more details of their findings in a paper published Monday in the journal Global Change Biology.

Researchers believe the presence of too much summer sea ice near the colony for the five breeding seasons between 2004 and 2010 made it more difficult for adult penguins to find food for their chicks. This, in turn, resulted in very few chicks surviving those years.

Adélie penguins need just the right amount of sea ice to survive—too much sea ice makes it harder for them to forage for food. Courtesy of Louise Emmerson / Australian Antarctic Program

With fewer chicks maturing into adults, the colony’s numbers continued to decline. The increasingly smaller group of penguins then became more vulnerable to predators.

Penguins thrive in large colonies, so the shrinking numbers may have made it more challenging for the birds to navigate and find food. This is particularly true of fledglings, who leave their parents when they are just two months old to swim in the Southern Ocean for the first time. Without many other fledglings around, the young penguins may be more likely to become a meal for a hungry leopard seal.

“It may be that the old adage of safety in numbers is playing out for the fledglings in the vast and harsh Southern Ocean, although exactly why and how needs further investigation,” says Louise Emmerson, a seabird ecologist with the Australian Antarctic Division, in a statement.

Adélie penguin chicks Courtesy of Louise Emmerson / Australian Antarctic Program

In total, the researchers estimate the colony lost some 154,000 breeding birds across 52 islands that span the 62-mile coastline near the research station. What’s considered to be a good breeding season today is about 80,000 fledglings short of totals during the group’s peak in the early 2000s.

As is often the case with declining wildlife populations, one seemingly small change can trigger a downward spiral that’s difficult to slow or stop.

“It’s kind of a cascading thing that’s happened where there’s the initial decline in the number of chicks and, because there’s fewer of them, they’re more vulnerable,” Jane Younger, a biologist at the Institute for Marine and Antarctic Studies at the University of Tasmania in Australia, who was not involved in the study, tells the Guardian’s Lisa Cox.

An Adélie penguin and a chick Courtesy of Matt Pauza / Australian Antarctic Program

Of the 18 generally recognized penguin species, Adélies are one of five that live in Antarctica; four live on sub-Antarctic islands, and the rest live in other parts of the Southern Hemisphere, including Australia, New Zealand and Africa.

The Mawson penguin decline was somewhat of a surprise to researchers, because models had predicted that their numbers would continue to grow, just as they’d done for decades. This research reflects the critical importance of gathering long-term population data, which can give scientists a more accurate picture to inform conservation decisions, such as how best to manage krill fisheries.

Other populations of Adélie penguins in East Antarctica are stable or growing, whereas groups on the Antarctic Peninsula are in decline, a trend driven by climate change and human activity.

Whether or not the Mawson penguin population will bounce back remains to be seen. In the meantime, researchers plan to continue their studies, focusing on the factors that could be affecting fledgling survival during the young birds’ first winter.

“We are better off preventing impacts in the first place or trying to alleviate them before population decline is well-established, or the processes causing the decline become confounding and result in rapid population declines,” Emmerson says in the statement.

source: https://www.smithsonianmag.com/tag/birds/