The massive zebra herd, as the name suggests are a gigantic congregation of zebras that are almost always on the move for food, water and shelter.  Being very alert and observant on their surroundings, they only let their guards down to relax or sleep whenever it is safe enough for all of the group as a whole.  The herd as a whole can get very reactive and tempered around the sight or sound of predators, either fleeing away altogether or fighting against them in coordination to protect foals.