Use a photon weapon to destroy a Jackal's shield quickly. When you encounter a Jackal, run up and hit it with your weapon or get out a gun that uses bullets, not energy. When you are a far way away from Jackals and have a sniper, they will sit in the defense position and leave very little uncovered. You will notice that on the right or left is a small notch in the shield. Aim for it and the Jackal population will be severely decreased.