Maybe the Whitetails are either copying or following the same imperative some of the Mulies do. Some Mulies migrate, make the same journey year after year. The reasons my be varied and multiple, cooler at the higher elevations, better forage, fewer flies, whatever?
I used to hunt a Muley migration in California, you could predict where they'd be along the migration route pretty closely on a calendar. Even Fish and Game would have flexible seasons in certain areas so the hunters were always behind the migration and could harvest the stragglers-