Birds have bilateral symmetry. This means the left and right sides of their body can be divided into an almost exact mirror image of each other down the midline.
What is the ‘Midline’?
The imaginary line drawn down the middle of the body to divide the left and right sides is sometimes called the midline. It is another name for the axis of symmetry or line of symmetry.
Why do Birds Have Bilateral Symmetry?
The first, and most obvious, reason for having bilateral symmetry is it means birds can fly really well.
Thought Experiment One – Imagine the air flowing around a bird in flight with one wing bigger or smaller than the other. How would this effect the flight?
Thought Experiment Two – Imagine if one of the bird’s wings was a completely different shape to the other or if several feathers were missing from one wing. What would this do to the birds ability to fly?
The second, and not so obvious reason, is female birds loves symmetry!
Experiments have been carried out to show female birds prefer more symmetrical mates because symmetry is an indicator of ‘good genes’. Symmetry in birds is associated with speed, strength, ability to fight and protect the young.