From the Halo 2 Manual (Human Version): Excellent shots, the Jackals seem to be higher in status—if not necessarily rank—than the Grunts. They often will be found in defensive positions, fighting from behind their distinctive energy shields. A well used shield makes a Jackal a difficult target, but the notch they use to return fire provides a weak spot that can be exploited.
From the Halo 2 Manual (Covenant Version): Slight of build as they are, the Kig-yar [Jackals] remain a valuable fighting force. Excellent shots, and with their shields nearly invulnerable, the Kig-yar offer a great tactical advantage i ground combat. Faster and taller than the Unggoy [Grunts], they complement each other very well.
The Jackals, known as Kig-yar to the Covenant, are back in Halo 2 in their support role. Once again, they are the most annoying enemies to the player, since they actually take some time to kill. However, with the new dual weapon system in Halo 2, their removal is a little easier. Hit them with a charge blast, and finish them off with a few rounds from the Sub Machine Gun. As if you needed another reason to hate Jackals, they can now snipe with the Covenant Beam Rifle.