Twice as many emperor penguins live in Antarctica as was previously thought, a satellite mapping study has shown.

Scientists used Very High Resolution satellite images to estimate the population of each penguin colony.

The British Antarctic Survey (BAS) researchers counted 595,000 birds, almost double previous estimates of between 270,000 and 350,000.

On ice, the black and white plumage of emperor penguins makes colonies clearly visible in the satellite images.

The scientists studied 44 colonies around the Antarctica coast, seven of which were previously unknown.

BAS geographer and lead author Peter Fretwell said: "We are delighted to be able to locate and identify such a large number of emperor penguins. This is the first comprehensive census of a species taken from space."

The findings are reported in the online journal Public Library of Science ONE.

Scientists are worried that earlier spring warming is leading to the loss of sea-ice habitat for emperor penguins.