The number of golden eagles in Scotland has been kept down by new developments that have encroached on their territories.

Forestry plantations have had a much bigger effect on Scotland’s iconic bird of prey than previously thought, reducing its food supply by covering open ground and lowering its ability to produce offspring, researchers say.

They now warn that similar effects can be expected from new wind farms if they are allowed to proceed in golden eagle ranges.

While golden eagles have recovered to around 400 pairs across Scotland after decades of persecution, scientists believe the true number should be double the current amount.

The study, ‘Complex effects of habitat loss on golden eagles’, published by the British Ornithological Union’s journal, was undertaken by a research team from Scotland and England.

It found that by taking just 5% of an eagle’s range, developments could affect breeding and ultimately force it to abandon its natural habitat. When eagles were already struggling to establish a range and breed, losing just small amounts of open ground could cut food supplies to the extent of threatening their survival.

Dr Philip Whitfield, the lead researcher based at the Natural Research environmental consultancy in Banchory, said: “Previously, it was assumed that as long as you do not encroach on more than 40% of the eagles’ territory then it would be OK. That is not the case.

“If a forest or wind farm is sited on just 5% of the territory then it does have a knock-on effect. If you cut down a golden eagle’s food supply then you will have an effect on its breeding success. If this continues to happen then it may abandon the territory altogether.”

Foresters and wind farm developers should now make certain they know how well-established a golden eagle pair is before proceeding and whether they face competition from other pairs if they move on, Whitfield added.

“Anyone planning to encroach on eagle territory needs to know a lot more about the kind of pair they will be disturbing and take that into account.”

Around 500 wind farm proposals are either built or at various stages of the planning process in Scotland. Jason Ormiston, a spokesman for the Scottish Renewables Forum, insisted that wind farm developers do take account of golden eagle ranges before applying for planning permission.

“Developers take this very seriously and do their best to avoid or mitigate effects on golden eagles,” he said.

“At one development in Argyll, the developer created a new feeding ground for the golden eagles, and they appear to be happy with their new environment, although they have not bred yet.”

The Forestry Commission Scotland, which runs major plantations throughout Scotland and advises private landowners on setting up new forests, said it was aware that golden eagles could be affected.

It said it could not comment on the research until it had time to study it, but added: “If, however, the findings indicate improvements can be made to the information currently provided, then the commission, with Scottish Natural Heritage, will review the information guidance currently issued.”

Environment charities said any research which helps the understanding of golden eagle conservation should be welcomed. A spokesman for the Royal Society for the Protection of Birds said: “We’ve known for some time that extensive afforestation can affect eagle populations, and this research helps to build up a useful picture for land use policy.”

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