Noisy tricolored blackbirds can be found in fields and wetlands in the Pacific coast states, but they are losing habitat.

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.

Originally published on theconversation.com, part of the BLOX Digital Content Exchange.

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