There's a growing body of evidence that birds can detect magnetic fields like the one around the Earth, possibly by "seeing" them. And this, researchers think, accounts for how migrating birds, like reed warblers, manage to find their way, seemingly unerringly, half way around the planet. But it's more subtle than just using the magnetic field like a compass. What Oxford University's Joe Wynn thinks is happening is that the birds are pre-programmed by their upbringing to fly in a certain direction, but they use the angle - or inclination - of the Earth's field, to work out how far north or... Like this podcast? Please help us by supporting the Naked Scientists