Antarctic sea ice levels are perfect for emperor penguins, according to researchers, who have found the frozen continent has in the past been too cold for the flippered bird.
A team of researchers, including scientists from the University of Tasmania and the Australian Antarctic Division, has been investigating how emperor penguin numbers have varied over centuries.
Lead researcher Jane Younger said that despite emperor penguins being accustomed to temperatures of minus 30C, the last Ice Age seems to have been a snap too cold for them, when their population was about seven times smaller than in 2015.
"Due to there being about twice as much sea ice compared to current conditions, the penguins were unable to breed in more than a few locations around Antarctica," Ms Younger said.
"The distances from the open ocean, where the penguins feed, to the stable sea ice where they breed was probably too far."
The findings, being published today, suggest current sea ice conditions might be optimal for the emperor penguin population.
But researchers are yet to determine the impact of further global warming.