“Fair enough, if it was a select number of birds … ,” one farmer said to biodiversity writer Phoebe Weston during her trip to Scotland, “but when it’s mass murder, then it’s not acceptable.”

Out on the cold west coast, there is a heated dispute about one of the country’s most successful ever rewilding programmes: the reintroduce of sea eagles to their natural habitat more than 50 years ago.

The eagles, local farmers claim, are killing their lambs – by the hundreds. Yet there is no recorded evidence of even a single incident, and many conservationists insist it isn’t true.

So, Helen Pidd asks, what is killing Scotland’s lambs?