Grey squirrels are an introduced species and are still naive about predator pine martens. The grey squirrels are easier to catch than native red ones - so in areas where the pine marten numbers are recovering the grey population goes down while the red thrives.
www.theguardian.com/environment/2018/mar/07/return-of-pine-martens-could-save-britains-red-squirrels-say-scientists
Can You Name 5 More Songs? (number 2)