The jackals aren't nearly portrayed at their 100% peak performance in the game. In the books they could run really loving fast and their sniper eye was dead on. A marine was killed on patrol, it was a sniper jackal with a beam rifle that killed him from 3.6 km away. In the games, they were cannon fodder. Same with the grunts. To Spartans, they were easy pickings. Through the eyes of a marine, a grunt was about 4'8. A jackal was about the size of an average human male. Elites were about eight feet. Brutes were about eight to nine feet. Hunters could go anywhere from 10 feet to 15 feet given the environment.
In context though, the halo 3 jackals were more of a sniper breed. The storm jackals were more aggressive and were easily agitated.
It could be a change in gender maybe to? Female elites don't have the split mandibles but rather a human like mouth. What's to say that female jackals look more birdlike or look more lizard like?