A bird's lungs move air in one direction, making their breathing very efficient.

The longer version

A mammal lung is a dead-end bag. Air goes in and comes back out the same way, so fresh air always mixes with stale air. A bird lung is a set of rigid tubes with air flowing one way through them, while separate thin-walled air sacs act as bellows that push air along without exchanging gas themselves.

Because the flow never reverses, blood meets air that is fresher than in a mammalian lung, and gas exchange continues on both inhale and exhale. This is why birds breathe well at altitudes where a mammal would struggle. Bar-headed geese cross high mountain passes on the strength of it.

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.