Stickiness / by Chris Maynard

Try taking two flight feathers from the same side of a bird’s wing and put the front, leading edge parallel and over the trailing next feather, like it was on a bird. The pull them gently and you can feel the feathers grab. If you put the leading edge of a feather underneath trailing edge of its neighboring feather instead of on top, there will be no grabbing; they will just glide smoothly over each other.

These feathers stick together in at least three ways to help make the wing smooth and aerodynamic:

  1. The leading edges of the feathers let a small amount of air through as the bird flies, a little more air than comes through the trailing edges. This evens the pressures caused by moving air which would otherwise tend to pull feathers away from the smooth airfoil a wing is supposed to make for a bird to fly.
  2. The leading edge of each feather curves slightly down and the trailing edge faces slightly up. So when two flight feathers on a wing overlap, the leading edge grabs trailing edge of the next flight feather.
  3. The almost microscopic barbules on the leading and trailing edges of each flight feather sort of splay out which help to grab onto the next feather, further creating more of  a seal so the feathers stick together firmly in the wind.

Reference: Muller, V. and Patone (1998) Air Transmissivity of Feathers. Journal of Experimental Biology 201, 2591-2599