Every year, millions of birds make journeys that would leave any sailor amazed. Some fly thousands of miles across open ocean, with no islands and no landmarks to guide them, and still arrive at the exact same beach they left the year before. For a long time, people could not explain how the birds managed this. Then scientists made a surprising discovery: birds carry several built-in tools for finding their way. By day, many use the position of the sun; by night, they read the pattern of the stars, just as old sailors once did. Most amazing of all, birds can sense the Earth’s magnetic field, so a part of the bird works like a tiny compass that always knows which way is north. Using all these tools together, a bird can hold a straight course even in cloud and storm. A creature smaller than your hand carries a better sense of direction than most people ever will.

No right or wrong — close the screen and tell someone nearby what happened in this part. Can’t find anyone? Tell yourself out loud. The moment you teach it, you truly understand it.