They like freezing conditions, but the Emperor penguins struggled during the last Ice Age, a new study concluded. In fact, if they hadn't been able to change their breeding habits and even their genetic make-up, they might have not survived.
The Emperor penguin is the tallest and heaviest penguin on Earth, and it's endemic to Antarctica. Reaching 1,22 meters (4 feet), it's truly worthy of its royal name. But it's a tough life being a penguin, and it was even harder during the last Ice Age. Back then, 30,000 years ago, ice covered much more sea than it does today, which mean that penguins could only breed in a few special locations.
"The distances from the open ocean, where the penguins feed, to the stable sea ice, where they breed, was probably too far. The three populations that did manage to survive may have done so by breeding near to polynyas - areas of ocean that are kept free of sea ice by wind and currents," said Gemma Clucas from University of Southampton, one of the researchers.
By examining the genetic diversity of both ancient and modern Emperor penguins, scientists from the universities of Tasmania, Southampton and Oxford in Britain, and the Australian Antarctic Division were able to get a pretty good picture of how their numbers varied in time. At one moment, it's estimated that there were only three populations living in the Antarctic.
"We hadn't really thought about the fact that it would be too cold for them in the past," said Jane Younger, a PhD student at the University of Tasmania who was also involved in the study. "They live through life in minus 30 degrees Celsius (-22 Fahrenheit) now so they are pretty cold adapted."
They would have likely gone extinct if the ice age hadn't waned away. As the temperatures slowly started to rise 12,000 years ago, penguin chicks had a better chance of surviving the winter, and more potential breeding sites opened up. Paradoxally, it's the extremely low temperatures which they are so well adapted to that might have killed them.
"We were actually really surprised by this. What we had thought was that the ice age, because there was so much more sea ice, which they need (to breed), and because they are so cold-adapted, that this would probably be a good thing for them," Younger said.
In their study, one notable area is the Ross sea - a population survived at Ross sea because an area of ocean was always kept free of sea ice by wind and currents, allowing the penguins to feed and breed.
"The Ross Sea is probably really important," said Younger of the area on the Pacific Ocean side of Antarctica, which is considered the world's most intact marine ecosystem. They have survived there for at least the last 30,000 years and even when the environment has been really unsuitable in a lot of other places, the Ross Sea has been kind of a safe haven for them. The Ross Sea seems to come up time and time again as a really important part of the Antarctic ecosystem."
Journal Reference: Jane L. Younger, Gemma V. Clucas, Gerald Kooyman, Barbara Wienecke, Alex D. Rogers4, Philip N. Trathan, Tom Hart and Karen J. Miller. Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum. DOI: 10.1111/gcb.12882