How do song birds breathe to produce long periods of song?

We but Tony's question to zoologist Max Gray... Max - Well this is really interesting. There's a couple of things that birds have, or do, that allows them to do this. First of all the respiratory anatomy, the lungs and what allows birds to breathe is very different from mammals and from our own. Rather than having a chest full of lung that expands when they breathe, they have a lung that doesn't really expand and contract very much. But they have, coming off from that lung, nine air sacs which then fill up and have muscular development around them that allows them to be pushed in, basically like bellows, so they will then force air through these different air sacs to breathe. And what that allows them to do is to kind of have loads of little different pockets of air that they can push out when they singing which allows them to sing for a long time. That wouldn't give them a minute.

Chris - But why do birds have lungs which work because our lungs obviously work quite well. We've evolved over millions of years to have them working that way. Why have birds gone down a different route and have their lungs working differently?

Max - So they can breathe easily while they're flying because the flight muscles of a bird are right across their chest. That's why chicken breasts that we eat are massive muscles.

Chris - But chickens don't fly, do they?

Max - The used to. Ancestrally, something in a chicken's history used to fly. They'll flap a bit, they'll give it a go - that's how roosters get up on to the top of barns. So the air sacs are all there so that, basically, birds can breathe while they're flying and they don't just drop out of the air struggling for breath. But in addition to that, birds will also make what they call "mini breaths," which last for about thirty milliseconds (about a thirtieth of a second). They take these tiny, tiny, tiny little breaths, which are just enough air to put back into their system in the middle of a song that allows them to continue singing. And you wouldn't necessarily hear that unless you recorded it and slowed it down a lot. And it would just be tiny, tiny, little mini breaths that allow them to keep going.