A stoat is like a ferritt or weasel and as an introduced species they have reeked havok among the indigenous bird species, thats why the traps set and maintained by the dept of conservation.
The keas set them of because they can,its what they do to amuse themselves.Its very common when parking your car in kea country to come back to your car to find it stripped of wipers,window rubbers and arials etc.They are demolition experts with wings.Thankfully they only get them in the south island high country.