Many human beings have a hard enough time finding a place across town without the help of Google Maps. So how do birds manage to find an obscure location, potentially thousands of miles away with their little bird brains? Scientists are still working to definitively answer this question, but they have some theories.
First, many, but not all, birds migrate to the same general location year after year. Some even use the same places for pit stops along the way! They are able to do this because they have an internal map and compass of sorts that helps them figure it out. These come in the form of many different cues, Weckstein says, which helps them navigate. "It's like an airplane that has more than one GPS unit on it," he explains. "If one goes bad you have the backup to save you."
For example, he says that many birds migrate at night, so they use the stars and actual constellations to find their way. When the sun is visible, they also use its position in the sky to orient themselves.
Both of these methods are of course common ways that humans have navigated land and sea for most of time. However some birds can also detect the magnetic field generated by Earth's molten core, he says. Somehow, using this information, they are then able to figure out where they are and where they need to go. Some scientists theorize that birds may have pigments in their eyes, which "let them visualize the magnetic field," Weckstein says.
There's also some belief that birds' bills might also have structures that help them in the migration process. Then, there's the fact that birds who migrate during the day actually learn landmarks, which help guide them on their path again and again. All in all, it's pretty obvious that the whole "fly south for the winter" concept is much more complicated than most of us ever realized.