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Dear Dr. Staff: How do birds fly? I asked my mom and she described something about their beaks acting like helicopter blades, except that the beaks rotate so fast that you can't see them. (When I thought about it, I realized that I had never seen a bird's beak close up while it was flying, either.) I asked my Aunt Felicia, too, and she said something about their wings twisting around as they flap. I think a beak is a lot easier to twist around than a wing, because its smaller, and isn't covered with feathers. What is the real answer?

--Avian Inquisitor

Dear Avian: When you take a balloon and put it in water, it floats. If you take a bird and put it in air, it sinks. But not all the time. When birds are flying, they act like balloons. Birds have special lungs that can hold lighter-than-air gases (like helium, the gas that fills your balloons when they float, and hydrogen, the gas that blew up the Hindenberg). When birds want to fly, they take deep breaths, and only breathe out the less interesting gases, so soon they are lighter than air and float. When they let the lighter-than-air gases out of their lungs, they sink back to the ground. One problem that happens is that the lack of oxygen in their lungs makes them feel woozy. They flap their wings as exercise to keep their blood flowing so that they don't faint and crash to the ground. Yes, birds flap their wings so they can fly, but they could fly without their wings; they'd just crash into the ground.

--The Expert

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