I want to know the answer to the following question:
What percentage increase in flight distance will often be adaptive?
All the background I'm provided with is that "An example is the migration of continental populations of Swainson's thrush Catharus ustulatus, which fly far east across North America before turning south via Florida to reach northern South America; this route is believed to be the consequence of a range expansion that occurred about 10,000 years ago.". Is that enough to answer the question?
Answer: no