Only when these hominids had to travel between arboreal habitats would they find themselves walking bipedally, 'forced' to do so by their own anatomies.

“只有当这些人科动物在两棵树上的栖息地之间来回穿梭时，他们才不得不用两足来行走。由于他们骨骼的结构特点，他们是‘被迫’这么做的。”

So the modern birds' ancestors have the chance to explore arboreal habitats or predatory habitats or aquatic habitats kind of for the first time.

因此，现代鸟类的祖先第一次有机会探索树栖栖息地、捕食栖息地或水栖栖息地。