Detailed Instructions: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Q: What was once scarce or non-existent in the US before intervention?, Context: It has been possible to teach a migration route to a flock of birds, for example in re-introduction schemes. After a trial with Canada geese Branta canadensis, microlight aircraft were used in the US to teach safe migration routes to reintroduced whooping cranes Grus americana.
A:
Grus americana