Number of guillemots on Isle of May has “dramatically declined”

Guillemots have become the latest species to suffer a dramatic decline on one of Scotland’s most important island seabird havens, with numbers down by nearly a third this year.

Counts of guillemots on the cliffs of the Isle of May, in the Firth of Forth, show numbers on the colony have dropped from 22,113 birds at the last count in 2023 to 15,506 this year. Of these, it is estimated there are 6,686 nesting pairs.

The 30% decline in guillemots follows an 81% crash in the number of shags on the island, with both species thought to have been affected by climate issues.

David Steel, NatureScot’s reserve manager on the Isle of May, said: “This is a worrying drop in the population and it mirrors problems we saw and were reported last August when a starvation event was occurring with the species. Birds were seen close inshore, which is unusual, often swimming in shallow water and struggling to feed, leading to high mortality.

“As well as this the picture is complex as birds can also take a year off breeding and therefore not be counted as part of the population counts.

“If birds are not in good enough physical condition at the start of the breeding season due to various winter stresses — lack of food and poor body condition — then birds will not breed.

“As they are long living — guillemots can live beyond 25 years — those which survived will hopefully be back next season.”

Each spring, the Isle of May becomes home to up to 200,000 breeding seabirds including guillemots, puffins, razorbills and shags.

Guillemots breed in high density colonies, with nesting pairs often in bodily contact with their neighbours.

They make no nest as such and their single egg is incubated on a bare rock ledge on a cliff face. After the breeding season the birds spend the rest of the year at sea.