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.
My tribe mate got stunned by one these while he was peacefully getting ripped to shreds by 1 thyacoleo, a swarm of bugs and a pack of terror birds. Guess which one caused his death? The microraptor because it stung him and he couldn't fight back.
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.
Good Luck. I must say if you see these things running at you at the speed of light you have about half a second to get away before you get knocked off your mount and stunned. I just so happened to get knocked off by an Alpha raptor once.