I think it's a combination of a number of factors. It's still really fascinating to me how the grey squirrel's survival tactic pretty much seems like it's built on exploiting the survival tactic of the red squirrels.

I wonder if the grey squirrels adapted this behavior because of previous encounters with red squirrels, displacing them in the process, or if it's just "bad luck" for the red squirrels to run into grey squirrels who just happen to perfectly counter their survival tactics?