In the second link provided , the farmer mooted that it may have been "animal rights" people.
That set me thinking about something I last wondered about during the trend for letting farmed mink out of their cages.
Do the "activists" think, "Oooh look, a cuddly wuddly little domesticated animal with no survival skills. Aint that cute? I'll just go and release him into the wild so I can watch him frolick and play and run down the M1......."
I suspect that this kind of behaviour is more to do with selfishly reinforcing the "activists" self image than it is anything else.