Aerodynamics of avian flight.

Much of the awe that humans have for the flight of birds derives from our earthbound habits and our bias toward emphasizing visual cues for interpreting processes in the world. Although we move through it and breathe it, air is vastly less dense than our bodies, so it is fanciful to imagine moving our limbs in a manner that would enable us to support our weight in the air. Moreover, air is invisible to us unless we use special tools to reveal its flow patterns. As evidence of our visual bias, contemplate a strong wind. You probably form a mental image of leaves moving on tree branches, or dust swirling about in a tornado, in both cases, solids moving in response to the force of the wind rather than the essence of the wind itself.