American squirrels are bigger, stronger and more aggressive than the European red squirrels. They also carry a virus that kills off the reds, and are therefor a menace to the UK's native squirrel population.
As the reds numbers fall, hunters are trapping and killing grey squirrels to cull their numbers, and selling off the meat to high end butchers.
There's the usual complaint about how ethical it is to shoot a caged squirrel in the back of the head with an air rifle while there are other options available such as contraception ... not exactly sure how that would work but somehow I doubt it will be a bit more costly than this method.
Maybe this will help to bring hunting back into normality in the UK, I certainly hope so.