Imagine you are kidnapped, blindfolded and driven hundreds of miles from your home before being released. You have no idea where you are, but luckily your kidnappers have left you a compass. How do you get home?
This is the situation that homing pigeons and other migratory creatures regularly find themselves in. Scientists have long understood that these creatures somehow sense the Earth’s magnetic field and that this built-in compass gives them the information they need to navigate.
The problem, of course, is that a compass reading by itself is not enough. To find your way home, you need additional information such as a map or at least a bearing on which to travel.
