Puffin numbers plummet at Britain's largest colony

The number of nesting pairs on the Isle of May, Scotland, has declined from 69,300 in 2003 to 41,000, despite a steady rise in the population over the past 40 years.

Ornithologists had expected the number of breeding pairs to reach 100,000 this year.

In decline: Puffin numbers have dropped by almost a third since 2003

The cause of the downturn is not yet known, but researchers believe that climate change could be to blame.

It is thought that warmer sea temperatures and intensive fishing could be affecting the development of plankton which, in turn, could affect the amount of fish available for the puffins to eat.

The survey was led by Mike Harris, from the Centre for Ecology and Hydrology, who has been monitoring and studying the puffin population on May, in the Firth of Forth, for 36 years.

He said: 'Something worrying appears to have happened over last winter and probably the one before. Puffins appear to be joining the ranks of other seabirds in the North Sea that are suffering reduced breeding success and decline in numbers.'

Puffins sit near the top of the food chain and are generally able to feed on a range of creatures in winter.

But many of the puffins arriving on the island this year were underweight, which has raised fears for the state of birds nationally.

The RSPCA believes that the problem is widespread. Grahame Madge, of the charity, told the BBC: 'This fits in with other evidence that North Sea birds have been desperately short of food over several seasons.

'But these have been birds such as the Arctic tern and kittiwake, which only feed in the top part of the sea.

' is probably the best adapted seabird that the UK has; they're deep divers, they're specialists in going down deep into the water column to find fish, so it's troubling to find that they're encountering a shortage of food.'

Puffins on May are surveyed every five years by counting the burrows where they nest. The counts take place in late April after the birds have cleaned out their burrows and before the vegetation has started to grow over.

In past surveys the occupancy rate of the burrows was almost 100 per cent, but this year it was only 70 per cent.