How Do Birds Know Where To Go When They Migrate? 

Birds can travels thousands of miles between their summer and winter homes. Why don’t they get lost? Their secret is a sixth sense: magnetoreception.
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I’m Lauren, this is BrainStuff, and I have a topically relevant scenario for your consideration: Let’s say you want a change of scenery. So you set out with the clothes on your back, your innate knowledge of the world, and zip all else. No map. No smartphone. Nada. Would you be able to travel tens of thousands of miles, across oceans and continents? And then get back home a few months later?
Because lots of birds do this every year. It’s called migration. And often these birds go to the exact same summer and winter spots, using nearly the exact same routes, every time.
Ornithologists have speculated that birds might use a number of sights, sounds, smells, and learned social cues to get where they’re going. But young birds making their trip for the first time have been observed migrating successfully with no chaperones. What gives?
Research has revealed that migratory birds have vision-based magnetoreception: They can see magnetic fields. And Earth is lousy with magnetic fields.
Earth’s molten outer core is made up of iron alloys, which are swished around by heat coming up off of the solid inner core - and by the rotation of the Earth. That motion (plus the fact that iron is good at conducting electricity) creates a dynamo: A generator of electric and magnetic fields. Which basically? Makes Earth function like a giant magnet. North is positive, South is negative, and our planet is wrapped in slopes and curves of magnetic fields arcing between them.
And migratory birds can sense those fields! Experiments over the past couple decades have shown that birds prepared to migrate south will align themselves with magnetic south - even if you create an artificial “south” in a lab.
And furthermore: These birds see magnetic fields. Around 2010, researchers fit European robins with clear or frosted goggles, and found that the birds needed clear vision in their right eyes to navigate magnetically. Why not their left eye? No one knows.
Scientists are now studying what biological mechanism might be responsible for this. The popular theory goes that magnetic fields cause a chemical reaction in birds’ eyes that affect their sensitivity to light. So magnetic fields might show up as brighter or darker patterns spread out over everything the bird sees. Like a map on a heads-up display.
SOURCES:
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phys.org/news19...