Another vote for coyote, or canid of some sort.

I think that in order to get a definitive identification, you're gonna' need to open that mouse up......see what it's been eating, then determine where such a food source might be found, make a list of predators common to such an area, cross reference those animals against.....whistle

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.