the easiest way to kill them is to find a low spot that thier head would get close to the surface and shoot them with a rifle grenade a good spot would be like as ur walking up the big hill on the left the little ditch down thier if u hit thier shadow they should die
lol just shoot upwards out of the ground but be warned the hills on top block u on the bottom as well they also block your shots so you have to would around the hills that u see above u