From Halopedia, the Halo wiki
In battle, Jackals share many similarities with Grunts, but are far more intelligent. Like the Grunts, they are a weak subordinate race and are somewhat cowardly. Despite their efforts to assure the Covenant of their superiority over the Grunts, they often cower in battle and retreat with their shields up in the air.
Jackals with shields in the original trilogy are mainly seen wielding Plasma pistols, though in subsequent games other weapons became more commonplace, like the Needler. Until Halo: Reach, they were the only enemy that utilized the pistol's ovecharge function, and though other enemies now do that as well, they are still the primary employers of this technique. The Jackal's Point Defense Gauntlet is almost completely impervious to all kinetic firearms, such as human and Brute weapons, but if a plasma weapon is fired at it for an extended period of time it will easily deplete the shield. There are a few ways to approach them:
Sniper Jackals appear starting with Halo 2, where they are equipped with the Particle beam rifle, and from Halo 3 onwards they can also be encountered with the Carbine (or other mid-range weapons depending on the game). Sniper Jackals are best countered by defeating them at their own game. Find a headshot-capable weapon, then survey the area, looking for the signs of their presecence. Depending on the game, snipers will have a glowing helmet, a laser sight, or a different coloration. In absence of these, follow the trail of their shots, as they tend to stay in one place. When you find them, shoot their head before they have time to notice you.
Halo Wars Stat
In Halo Wars, Jackals play a powerful anti-infantry role, having been given the capability to inflict a number of casualties upon regular enemy infantry that are disproportionate to their own numbers, much like the UNSC Hellbringers-though having the advantage of longer range weapons. They are deployed in groups of two, and their default armament is the medium range Covenant Carbine. However, being geared towards a single role, the effectiveness of Jackals against armor and aircraft is highly limited, and will easily fall victim to vehicles. However, Infantry do, generally, defeat aircraft and the Jackals, in groups, will easily destroy enemy aircraft. Like all units in Halo Wars (Excluding the Vulture and Scarab), Jackals have multiple upgrades as listed below in the precise order researched:
Changes from Halo: Combat Evolved to Halo 2
Changes from Halo 2 to Halo 3
Changes from Halo 3 to Halo 3: ODST
Changes from Halo 3/Halo 3: ODST to Halo: Reach
Changes from Halo: Reach to Halo 4
Changes from Halo 4 to Halo 5: Guardians
Changes from Halo 5: Guardians to Halo: Infinite