The sustainability of the world’s largest gannet colony, on Bass Rock in the Firth of Forth, may be threatened by four offshore wind farms approved for construction nearby, scientists say.

“From a long-term perspective, we need to know how many birds will end up being killed and what effect that will have on the population,” said Prof. Keith Hamer from the University of Leeds, who led the study.

Hamer’s team have confirmed that gannets forage at the wind farm sites.

That might not be a problem in itself – when approval was granted, the best evidence suggested that the birds rarely fly high enough to be struck by turbine blades.

But those estimates were based on birds commuting to and from foraging sites. The new research found that they fly much higher when actively foraging.

This increases projected mortality rates up to 12-fold, to 1,500 deaths annually, which approaches the threshold at which the population would be expected to decline.

Liz Humphreys, a seabird researcher with the BTO, agreed that declines are a possibility. “But you’ve got to be really careful in the assumptions you make with population models, particularly when it’s about the impacts of development,” she said.

For example, it is not known if foraging birds steer clear of wind farms, and if they don’t, whether they can avoid collisions with the turbines. “There are so few turbines currently built within the core foraging area of gannets that it’s difficult to judge that,” said Hamer.

The wind farms are currently being contested in a Judicial Review instigated by the RSPB, and so both the RSPB and the government regulator Marine Scotland declined to be interviewed.

“If this paper had been published six months ago, it would have been included in the Judicial Review and it would have been gone through with a fine-tooth comb,” said Humphreys.