For centuries, bird migration was a mystery – a tech revolution is changing that, and could help save these amazing creatures

Noisy tricolored blackbirds can be found in fields and wetlands in the Pacific coast states, but they are losing habitat. John Anderton/The Atlas of North America's Migratory Birds

For more than 2,000 years, scientists have scratched their heads over one of the most basic mysteries of the natural world: Where do birds go?

Billions of birds appear and disappear with the seasons every year. Early naturalists offered explanations for the disappearances that today seem fantastical: Birds transformed into other species, one theory went. Others suggested they hibernated underwater or even migrated to the moon.