Flight feathers are unique structures that are credited with being the primary evolutionary development that enabled birds to fly. They must be able to withstand the large forces that occur during flight and they must be lightweight. Unlike airplane wings, which are solid, bird flight feathers are formed from a web of barbs projecting from a central stiff vein. This design balances the large surface area needed for lift with strength and extreme lightness.
Feather barbs are thin and flexible and have a number of features to protect them from permanent damage. Barbs are linked with a series of grooves and hooks that zipper up like Velcro, enabling them to detach when forces become too great and to be easily repaired later. Barbs are ribbon shaped, meaning they are stiff in one direction and flexible in the other. They are stiff in the direction under which they are loaded during flight, but very flexible in the other direction. This works because the hook and groove mesh holds them in place and counteracts their side-to-side flexibility. At the same time, if forces do become too large and the barbs are at risk of permanent damage, they are still able to twist, presenting their flat flexible side to the force, bending and spilling the load. In this way, they flex out of the way when necessary, reassuming their prior position later and zippering back up again, as good as new.Edit Summary