Never tried such an experiment but I can say without reservation that if I controlled 150 acres and wanted Grey but not Red squirrels, I would shoot every Red I could get my sights on. It's only 150 acres, you're not going to hurt the species.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.