Many birds make long journeys twice each year as they migrate between
their winter and summer homes. Arctic terns fly more than 10,000 miles
from the South Pole to northern Maine. Tiny little hummingbirds fly
nonstop over the ocean for 500 miles. How do they know which way to fly?
Why don't they get lost? Read and find out the many ideas scientists
have come up with to explain this mystery.