Numbers are down to about 41,000 breeding pairs this year from almost 70,000 pairs in 2003.

Researchers believe the decline is linked to changes in the North Sea food web, perhaps related to climate change.

Birds are also arriving underweight, which the RSPB describes as "worrying", because puffins are generally able to feed on a range of creatures in winter.

Losing count

The Isle of May, in the Firth of Forth, is home to the UK's largest single puffin colony, although more birds overall nest in the St Kilda archipelago.

Mike Harris, from the Centre for Ecology and Hydrology, has been monitoring and studying the Isle of May population since the 1970s, labelling individual birds with rings to follow their progress.

After decades of spectacular growth, he now believes the colony is in decline.