Puffins are to be fitted with satellite transmitters for the first time in an effort to understand a worrying decline in their numbers in the last five years.

Scientists are to fit tiny global positioning system (GPS) devices to the sea birds' legs to work out what is happening to them, reports the Daily Telegraph.

Possible reasons include climate change causing sand eels, puffins' main food source, to move north. Pollution can also affect numbers and competition from other species such as gulls.

Puffins on the Farne Islands will be fitted with GPS this summer. When the data is collected from returning puffins the following year it will provide clues to the kind of feeding grounds the birds have been to and the threats they are exposed to.

David Steel, National Trust Head Warden on the Farne Islands, said puffins were breeding successfully so it was essential to find out what could be causing the death of the birds out at sea.