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How do birds fly?

a rough legged hawk soaring in the blue sky
Wirestock from Getty Images

Why do birds fly? How do raptors soar? Why do some birds fly in the shape of a V? Why can’t some birds, like penguins, emus and ostriches fly? Why do hummingbirds fly so fast? We answer all of your questions about birds and flight with help from Anna Morris of the Vermont Institute of Natural Science and Bridget Butler, the Bird Diva. And we get a preview of our new education series But Why: Adventures! Northeast Nature. Educators: learn more about But Why: Adventures! Northeast Nature and sign up for free access to the series!

Download our learning guides: Video | PDF | Transcript

  • There are a few theories of how birds started to fly. One theory is that birds started flying by leaping and gliding as they ran along the ground, similar to how turkeys fly today. Another ground-up hypothesis is that these dino birds used wings and feathers to help them climb up steep slopes or tree trunks–kind of like running up a wall, and that evolved into flying. The other main theory is a tree-down theory: that birds used feathers and wing structures to help them glide from tree to tree or from a tree to the ground, the way flying squirrels do today, and that eventually they evolved to be able to fly longer distances.
  • Birds’ bodies are adapted for flight. Bird wings are shaped like an airfoil. An airfoil is a shape that is designed to make flight possible and efficient: we call that aerodynamic. It’s a curved surface, rounded on top and thicker in the front, and then gradually sloping back to be very narrow. The rest of the bird’s body weight is centered in the middle of its body. Most birds have bones that are hollow and light. 
  • Birds have to flap their wings to get the air moving around the wings. This generates thrust. Once the air is moving, the air going over the top of the wing has to travel farther and faster than the air under the wing because of that rounded shape. So there’s less pressure on the top of the wing and the bird generates lift!
  • Hummingbirds are unique in the bird world because they can fly backwards and forwards and they can hover for a long time. They actually beat their wings in a figure 8 pattern, which means they’re pushing air both forward and back (and down), allowing them to generate that force called lift in both directions of their wing strokes. They can beat their wings 90 times per second! 
  • Geese fly in a V to conserve energy! The bird in front takes the brunt of the wind as it pushes through the air, and the rest of the birds fan out slightly above and behind each other, taking advantage of the smoother air to fly with less effort. When the first bird gets tired, someone else takes a turn in front.
  • Most kids have noticed that penguins are birds but they don’t fly. Their ancestors flew, but modern day penguins don’t need to fly because all of their food is in the water. Their wings have evolved so much over time (in fact, they are the only birds that can’t bend their wings) that many people now think of their wings as flippers instead.
  • And here’s a vocabulary word for you: exaptation! You probably know what an adaptation is: a change in a living organism that allows it to better survive in its environment. Exaptation is when an animal takes something that evolved for one reason and uses it in a new or different way. 
  • You might think feathers are an adaptation for flying. But dinosaurs had feathers long before they could fly. Feathers probably evolved as a way to keep warm, as insulation. But they became essential in the evolution of flight–a new use. So feathers are an exaptation!

Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.

But Why is a project of Vermont Public.

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