They prefer freezing conditions but Antarctica's emperor penguins may have struggled with the cold during the last Ice Age when temperatures cooled, a study suggested Monday.
Researchers looking at how climatic changes have affected the highly cold-adapted penguin -- the tallest and heaviest of all penguin species -- over the last 30,000 years suggest that there were only three populations in the last ice age.
But as temperatures have warmed up since then, the species has flourished and there are now seven times more of the penguins in many more locations, said joint lead researcher Jane Younger.
"We hadn't really thought about the fact that it would be too cold for them in the past," Younger, a PhD student at the University of Tasmania, told AFP.
"They live through life in minus 30 degrees Celsius (-22 Fahrenheit) now so they are pretty cold adapted."
By examining the genetic diversity of modern and ancient penguin populations, scientists from the universities of Tasmania, Southampton and Oxford in Britain, and the Australian Antarctic Division were able to estimate their numbers over time.
They found that numbers began increasing over the last 12,000 years when temperatures rose by an average of about 15 degrees Celsius and as the amount of sea ice around Antarctica began to reduce.
Younger said the warmer temperatures likely gave penguin chicks a better chance of surviving the winter -- when temperatures would have dropped to minus 45 degrees Celsius during the ice age.
Too much sea ice could have also reduced the locations for breeding, while a shrinking of the ice would have allowed them easier access to the open ocean to feed, she said.
"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," she said.
Emperor penguins, which can get heat stress with temperatures above zero, breed during the winter, with the males keeping the egg safe and warm during the cold months.
"What happens occasionally is that the egg will get dropped onto the ice, and these days they can usually get the egg back and it will be alright if it was not out too long," Younger said.
"But the temperatures during the ice age were about 15 degrees colder so... if the egg was dropped it would have been in pretty serious danger almost straight away. And the same thing once the chicks have hatched out of the egg, they need to be kept warm throughout the winter."
The researchers believe a population survived in the Ross Sea region because an area of ocean was always kept free of sea ice by wind and currents, according to the study published in Global Change Biology.
"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."