View From The Shed by Shaun Finnie - EVERY BREATH YOU TAKE

EVERY BREATH YOU TAKE

If you read these blogs regularly you'll know that there are some funny ones, some serious ones and even some sad ones. There are some full of facts and some full of my own personal views (from the shed). Some are frivolous (because I do like a good frivol) and others are hard science that makes my head hurt. This week's is one of the latter. Make sure you read it somewhere nice and quiet because you're going to need to concentrate. With apologies to my 1980's O-level biology teacher, here's Volunteer Shaun's Handy-Dandy Guide to How Birds Breathe.

You know how your own breathing works, right? You inhale and take air into your body through your nose or your mouth. This air passes down your trachea (also known as the windpipe) and into your lungs where a process called Gaseous Exchange takes place. This is when oxygen is absorbed into the bloodstream to be passed around your body, and at the same time carbon dioxide is filtered out of the blood to leave the body when we exhale. The lungs and the muscles around them work like bellows, expanding and contracting to push air out and pull it in. Are you with me so far? I hope so because you've been doing that all the time you've been reading. This is how you, me and every other mammal breathes and it works pretty well most of the time.

Birds however, breathe in a slightly different way, one that is more useful for their feathery little bodies. They still breathe air in through their nostrils and (to a much lesser extent than mammals) their mouths, and the air then goes down the trachea into the lungs. So far, so like you and I but this is where things get a little complicated. Hang with me though, you can grasp this. If you can understand the offside law in football then this is going to be a doddle.

It's sort of an internal circular breathing system. If you've ever watched a bagpiper or didgeridoo player keep up a prolonged note for a seemingly impossible length of time, you'll have seen a decent approximation of how birds breathe. It's all about the airbags and each of our avian friends has nine of them.

When a bird takes a breath, some of that air goes into the lungs as you'd expect but some of it bypasses these lungs and is temporarily stored in a series of air sacs running down the bird's back. Imagine these as a group of balloons all strung together. It's these air sacs that expand and contract during breathing. The bird's lungs themselves are much more rigid and inflexible than our own and hardly change shape at all during the respiratory cycle.

There is a second set of air sacs positioned in the bird's chest. These too inflate and deflate, pulling oxygen-depleted air from the lungs and passing it back up the trachea to be exhaled. As if all that wasn't strange enough, here comes the really weird bit; prepare yourself... At the same time as the bird is breathing out, the first set of air sacs – the ones at the back – squeeze the air that was stored during the previous inhalation into the lungs; so effectively the bird has two lots of fresh air from every single inwards breath. This is much more efficient than our own breathing cycle as air only ever passes through the bird's air in one direction. The dirty air full of carbon dioxide never goes back into the lungs. Instead they have two chances to extract as much oxygen as possible from each breath. That's especially useful when they are flying at high altitudes where the oxygen makes up a much smaller percentage of the air.

So to recap... Air comes in through the nose. Some of it goes straight to the lungs, but some goes into the rear air sacs. The bird breathes out and clears the dirty air from its the air sacs in its chest. This pulls new air from the lungs from which the oxygen has been extracted. The lungs are then replenished with the fresh air that has been stored in the rear air sacs. Simple!

This respiratory cycle works the same for every bird on the planet from mighty Condors of South America to the most humble Great Tit on your bird feeder. And it gets better. Birds obviously need to be at their most oxygen-efficient when they are flying, compared to when they are (for example) just bobbing around digging for worms on a lawn. So the physical mechanism of flight – the pumping of the wings up and down – actually helps to increase the inflation and contraction of the air sacs, making them work harder at getting that fresh air into the lungs and the useless air out of them.

So next time you see a bird effortlessly going about its business, just spend a moment to imagine all those little air sac pumping away like a steam engine beneath the skin and feathers. Once again, nature fascinates and impresses me more than I can say.

I really hope I explained it clearly enough. If not, ask me to act out the full thing next time you see me at Old Moor's Welcome Shed. I guarantee that one of us will end up out of breath.