If you hear one scrwam or you just hear battle music flare up out of nowhere, dismount IMMEDIATELY. They can only stun you while you're on your mount so if you get off before it reaches you it won't stun you when they hit. Its much better to be off your mount for a bit during a battle rather than being stunned AND dismounted in the middle of a battle.
They seem to only be aggressive when you are on your mount. Dismount before approaching or else you will find your self thrown off and Stunned. Walking forward and backwards quickly allows you to "hula hoop" an attacking Micro, giving you time to dismount and avoid the stun.