Bird feathers are famously light, but they’re also strong, holding up under tricky flying and high winds. They’re made of beta keratin, a tougher version of the keratin that makes up human fingernails and hair. They also have an intricate branching structure that makes them highly flexible and free of unnecessary weight.More info and transcript at BirdNote.org. Want more BirdNote? Subscribe to our weekly newsletter. Sign up for BirdNote+ to get ad-free listening and other perks. BirdNote is a nonprofit. Your tax-deductible gift makes these shows possible.