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"There's been a huge increase in their willingness to commit violence to farmers and gamekeepers, anybody who tries to stop them doing what they do."

The organisation said that was because gamekeepers are trying to protect their grouse, pheasants and partridge - and the profits they bring.

A part-time gamekeeper and his son who raided peregrine falcon nests have been banned from keeping birds of prey.

Natural England, which also monitors the birds, said they were often targeted by gamekeepers because they eat grouse.

Some of Dr Watson's research on the Sphinx drew on information handed down by generations of people who worked and visited the Cairngorms, including gamekeepers.