Counts of Atlantic Puffins Fratercula arctica in the Firth of Forth, south-east Scotland in 2003

The numbers of Atlantic Puffins breeding at three colonies in the Firth of Forth were estimated in 2003. The Isle of May held 69,300 occupied burrows, making it the largest single colony in Britain and Ireland. This population increased at an average rate of 10.9% per annum between 1970 and 2003. Similarly, numbers on Fidra (1466) increased by an average of 9.5% per annum over the period 1976-2003. In contrast, the count of occupied burrows on Craigleith (12,100) was less than half of the 1999 estimate. This decline appeared to be due to the rapid spread of an alien plant, the tree mallow Lavatera arborea. The geographically distinct population of Atlantic Puffins in east Britain between the Moray Firth and Flamborough Head was estimated at 130,000 occupied burrows in 2003, representing an average rate of increase of 6% per annum over the previous 30 years.