Droppings put penguins on the map

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Scientists have located 38 emperor penguin colonies in Antarctica by using satellites to look for stains from the animals' droppings.

It is impossible to track the penguins themselves using standard satellite imaging because they are too small.

However, penguins cluster for up to eight months on sea ice; as their guano builds up it leaves a reddish-brown mark on sea ice that is easier to spot.

The survey of colonies is published in Global Ecology and Biogeography.

"We were mapping one of our bases on an ice shelf, and we knew there was a penguin colony close to there," said Peter Fretwell, a geographer at the British Antarctic Survey.

Satellite images clearly reveal the penguins' movements

"I was using a satellite image as a backdrop for the map and it happened to have a reddish-brown stain on one of the creeks that was a possible location for the emperor penguin colony."

"It was quite a lucky find because just a few months beforehand, we had made a mosaic of these satellite images of the whole of Antarctica, so we could go round and track all the colonies."

Comparing their satellite image stains with the known locations of emperor penguin colonies, the team identified 10 previously unknown colonies, and found that six known colonies had recently moved a significant distance.

Six more known colonies had disappeared altogether.

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"We know that emperor penguins rely on sea ice to breed - like the polar bears in the Arctic depend on sea ice for their hunting. Although the sea ice at the moment is reasonably stable, we know that in future decades it will decrease rapidly," Mr Fretwell added.

"We need to know where they are and to assess how many there are before we can really work out how threatened they are by climate change."