They prefer freezing conditions, but Antarctica's emperor penguins may have struggled with the overwhelming cold of the last ice age, a study said on Monday.

Researchers looking at how climate changes have affected the highly cold-tolerant penguins - 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 since then, the species has flourished. There are now seven times more of the penguins, and in many more locations, joint lead researcher Jane Younger said.