When I was in school I learned in the winter birds fly south. In the summer birds fly north. This isn't exactly the case - in fact, it is really not the case at all. There is much more to migration patterns than the birds simply flying south and the birds simply flying north. There are a lot of factors that go into how and when a species or even an individual bird migrate.
Never fear though..
Birds and Blooms has you covered with their article Bird Migration Secrets Revealed
In it they discuss different migration patterns, some of the strange things happen during migration and more about who goes where - and it doesn't just happen in Spring and Fall!