How Do Birds Fly?

It’s something I’m sure we’ve all done on several occasions. Staring up into the sky and wondering ‘how the hell do birds actually fly?’ They always look so awkward and heavy on the ground yet, when in the air, they soar gracefully – seemingly defying gravity.

The Basics

For a bird to actually be able to take off at all it first needs to overcome the two forces which want to keep it earthbound. The first of these is gravity, the force which keeps our feet on the ground.

The second is drag. This results from air resistance (or friction) against a moving object. Too much of this would make flight impossible for a bird, as it would be unable to travel forwards.

Lift and Thrust

So, if these are the problems a bird faces when flying then what are the solutions? Well, to solve issue number one, gravity, a bird needs to generate an opposite force which will keep it in the air. This is known as ‘lift’.

The obvious assumption is that when a bird flaps its wings downwards it creates lift. However if this was the case then the upstroke would presumably generate an opposite force, thus knocking the bird out of the sky.

 In fact the creation of lift is a much cleverer process. If you were to take a cross-section of a bird’s wing it would look like a teardrop. In scientific terms this is known as an ‘aerofoil’. As a bird moves forward air flows over both the top and bottom of its wing. Yet, because of the shape, pressure does not build up equally on both sides. More is concentrated beneath than above and because of this imbalance of pressures lift is created. It is because of this that a bird is able to soar through the sky without flapping its wings and it is this same physics that are used to allow planes to fly.

So, we now know how a bird keeps in the air but how does it actually go about moving through it? To overcome the force of ‘drag’ a bird must create a counterforce, this is known as ‘thrust’. In order to do this a bird uses its feathers. Yes, they’re not just there for decoration. In fact feathers represent a highly sophisticated piece of evolution. Each one is, once again, a smaller aerofoil in shape. When a bird flaps its wing downwards the feathers are twisted into a more vertical position and forward facing position. As a result when air travels over them thrust is created which pushes the bird forward through the air.

As well as this birds have several special adaptations which enable them to fly. Their bones are actually hollow, meaning that they have much less weight to carry in the air. They also have a special bone in their chest called the ‘Furcula’, which is more commonly known as the ‘wishbone’. You might remember seeing it in that turkey you had last Christmas. It acts as the centre of the bird’s exceptionally sophisticated muscle and bone structure, giving it the ability to flap its wings.
So, overall, the ability that birds have to fly represents the culmination of an exceptionally long and impressive line of evolution and adaption. Sadly, we’re just going to have to settle for planes, as our chances of taking off into the wide blue yonder at some point are none-existent.