Whooping cranes once lived all over North America. But by the 1940s, only one tiny flock was left. These beautiful birds were in danger of dying out. Scientists decided to start a second flock of whooping cranes, but they had a serious problem to overcome. Whooping cranes need to migrate. They live up north in summer, then fly south to spend winter in warmer locations. Usually young cranes follow older cranes when they migrate. How would the scientists teach the new flock where to go?