who ever said that they become steril, is an idiot. during some stage of the ice age, a continental glacier covered and split northamerica into coastal regions only. the deer were spliy. the eastern ones stayed whitetails and the western coast evolved into the bnlacktails. when the glaciers receeded, the two deer met up, creating Mule deer.
i wish i knew which book i read this from, but look up your question and you'lll find out that what i siad is pretty darn accurate.
the only eagle with enough power and speed to kill and gut you with one shot