Birds have hollow bones that keep their skeletons light enough for flying.

The longer version

Many bird bones are pneumatic. They are hollow shells of compact bone with internal struts, and in places they connect to air sacs so air passages run right through the skeleton. The struts keep the bone from buckling, so the outcome is a stiff lightweight tube rather than a weak one.

Being light matters more for a flapping flier than being strong, because every gram has to be lifted on every wingbeat. The air sacs do double duty, feeding the one-way lung system. Birds are not all hollow to the same degree; divers and loons have denser bones that work as ballast underwater.

Where this entry sits

Here you will find feathered trivia about flight, migration, nests, eggs, and the songs birds sing. Expect short surprising facts on penguins, owls, hummingbirds, and other familiar birds from gardens, forests, wetlands, and distant coastlines. The full list sits on the Birds page, where every entry is listed in order.