Why Do All the Babies in This Massive Penguin Colony Keep Drowning?

Emperor penguin chicks in Antarctica.
Emperor penguin chicks in Antarctica.
(Image: © Roger Clark ARPS/Shutterstock)

The second-largest colony of emperor penguins (Aptenodytes forsteri) in the world appears to be collapsing, after rough seas drowned all of its babies three winters in a row.

The Halley Bay colony once accounted for 5 to 9% of the global emperor penguin population, according to the British Antarctic Survey (BAC), which reported the catastrophe. That amounted to about 15,000 to 24,000 adult breeding pairs. But in 2016, the sea-ice platform on which the colony was raising its babies collapsed during rough weather, throwing infant penguins unable to swim into the frigid water. In 2017 and 2018, the rough weather pattern repeated itself.

"For the last 60 years, the sea-ice conditions in the Halley Bay site have been stable and reliable," the BAC said in a statement. "But in 2016, after a period of abnormally stormy weather, the sea ice broke up in October, well before any emperor chicks would have fledged. This pattern was repeated in 2017 and again in 2018 and led to the death of almost all the chicks at the site each season." [In Photos: The Emperor Penguin's Beautiful and Extreme Breeding Season]

The birds arrive at the site from their summer sea jaunts each April to breed; for the resulting chicks to survive, the site has to remain stable throughout the Southern Hemisphere’s winter, which lasts until December. These findings, based on satellite images and published April 25 in the journal Antarctic Science, were verified when researchers visited the region.

By 2018, a handful of adults — a "few hundred," or about 2 percent of the original population — turned up at the Halley Bay site, the researchers reported. The remaining colony appeared in disarray, with adults moving closer to the ice edge than is typical, and was difficult to count scattered among the roughened chunks of ice.

"Whether the adult birds here were failed breeders or non-breeders is difficult to assess from imagery alone," the researchers wrote.

The good news is that at least some of the colony appears to have moved, rather than died out. The Dawson-Lambton Glacier colony 34 miles (55 kilometers) to the south has significantly swelled in numbers since the devastation of Halley Bay, the BAC reported. That colony, which had hit a low of just 1,280 pairs in the 2015 season, swelled in each succeeding year. In 2016, it reached 5,315 pairs. In 2017, there were 11,117 pairs. And by 2018, a full 14,612 pairs set up camp at the site.

Those numbers are still lower than the original Halley Bay total, but suggest that a significant number of penguins have figured out that it's better to move than return to the especially dangerous site.

Long-term, the researchers noted, there's reason to suspect bad winter weather might be a new climate-rated threat to penguin populations. While the data is incomplete, September 2016 included the lowest atmospheric pressure in the region for that month in 30 years, a driver of storm activity. At the same time, the average wind speed was the highest it had been in that time frame. This research, they wrote, will help them further understand how penguins will react to the world has it keeps warming and changing.

Originally published on Live Science.