The Terror Birds are the secondary antagonists of the Walking with Beasts episode Sabre-Toothed World. Based loosely on the real prehistoric Terror Birds, these Terror Birds are shown to take pleasure in hunting harmless Smilodon cubs and wait til the adults aren't around.
The Terror Birds hunt in packs and are flightless birds, but are capable of running at full speed. They have hooked wings which they can use to fight with. Their beaks and claws are powerful weapons.
The Terror Birds are first shown when one is stalking a Smilodon cub, and waits for it to get lost, but then suddenly when it is about to pounce an adult Smilodon runs out and roars at the Bird. The Terror Bird is soon outnumbered and flees.
More Terror Birds appear, attacking a pair of infant Doedicirus, ancient armadillos, which are soon protected by the mother, which makes the Terror Birds retreat humiliated. However the Terror Birds get a victory when they find the body of one of the usurper Smilodon brothers nearby and claim what is left of him for their dinner.
The Terror Birds are eventually scared off by outcast Smilodon Half-tooth when he claims a Doedicirus body for himself.
- The Terror Birds are seen in a very black and white view as the "bad guys" in the story with the Smilodon being the "good guys", even though two of the main villains are themselves Smilodon, however, the reality probably was that Smilodon and the Terror Birds were as bad as each other.
- The entire scenario in the story is rather like how criminal gangs function nowadays, when the king is down, others will take over. Thus the Terror Birds could be seen as a rival gang.
- The Terror Birds' relation to Gastornis, the antagonist of episode 1, is unknown. Although they are most likely descended from the Gastornis.
- The Terror Birds form a trend of giving birds a bad name in the Walking With Beasts series, starting with Gastornis.