Flightlessness, in most cases, evolves after a bird species begins to settle on predator-free island. To match their new behavior, their bones – once hollow to minimize weight – become dense, sturdy feathers become fluffy, and their wings either shrink or disappear completely.

THIS IS COOL. I WANT TO LEARN SOMETHING ELSE, TOO!

Video via – TED-Ed
Further Readings and References @ Bird Academy, Wikipedia (Feather), NatGeo

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