Hi guys attached is my achievement guide for Fowl Hunt. It's pretty straight forward, all you have to do is load Oni Alpha Site at rally point Charlie and grab a shotgun of a marine. The shotguns spawn randomly so you may need to reeled the rally point a couple of times. Then play through the mission until you get to the top of the bugger infested elevator. The outside area you come to is where the jetpack brutes are and you simply need to get the killing blow on three of them with the shotgun to get the achievement.
Hopefully this helps!