Birds Do Have Hollow Bones, But It’s Not to Make Them Lighter


If you’ve ever put any thought into why birds have hollow bones, you might have thought it was to help them fly – lighter bones are easier to lift, after all.

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Makes sense, but that’s not the real deal.

Hollow bones are actually an adaptation to assist birds’ lungs. Basically, birds need so much oxygen to fly, their bones have become pneumatized, which means that there are air spaces in them (like our sinuses).

Although there is still much to learn about the physiology of animals, we do know birds’ hollow bones have little to do with weight. Their skeletons don’t weigh any less than other animals of similar size. In fact, bird bones are harder and denser than other animals’ bones, so they won’t be fragile.

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Researcher Elizabeth Dumont, from the University of Massachusetts Amherst, acknowledges this kind of bone structure helps birds fly for another reason.

Many other studies have shown that as bone density increases, so do bone stiffness and strength. Maximizing stiffness and strength relative to weight are optimization strategies that are used in the design of strong and stiff but lightweight man-made airframes.

Back to how bird bones are pneumatized.

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Matt Wedel, of the University of California Berkeley, tells us that as young birds grow into adults, the air sacs serving as lungs grow offshoots that form into little hollows in their bones. The air sacs stay attached to the offshoots, while also remaining in use as lungs. Birds’ peculiar physiology both strengthens their bones and allows them to take in oxygen while both inhaling and exhaling at the same time, which is pretty damn cool.

And without the ability to be taking in oxygen all the time, they probably wouldn’t be able to perform the physical exertion needed to sustain long periods of high altitude flight.

As it turns out, from their little first breaths, baby birds are actually preparing for the skies.