A terror bird is hard too tame due to being very fast and they come in trios. Plus you have other dangerous dinos they might aggro on you or them. Or they might aggro on the creature themselves. All you need are bolas, tranq arrows or club, prime meat or meat or if your lucky to find a sheep around since they mainly spawn in the redwoods of the island, you can give them mutton (raw or cooked).

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