This summer a naturalist in the Kern River Valley was talking to a bunch of us field tech's about the mysteries and evolutionary feet of feathers. Jon Schmidt had been collecting feathers since he was a kid, and taught us the basics of identification, and started to get us to think about how this particular vertebrate body covering contributes to the incredibly diverse form and function of birds. In short, feathers are a marvel. They are amazing; with a capital A.
Feathers are downy soft, or stiff. They are fused, fringed, barbed, or flattened. They can be as small as a pencil point or larger than a human body. They can be vibrantly colored, or dull and lackluster. They are used to attract or repel members of the opposite sex or predators. They can hold in water, or repel it. They can whistle, snap, vibrate, hum, snap, or bristle.
Again, capital A.
Since I find myself with a more than usual abundance of free time as of present, I was excited to stumble across Destin's Smarter Every Day: a youtube series this guy interested in science decided to create and use as a conduit for doing cool science shit, and it is pretty sweet.
In How Bird Wing's Work, Destin debunks popular conceptions of bird flight using computational fluid dynamics. Essentially, the bird wing is a biomechanical check valve; on the downstroke feathers overlap to create a boundary layer where air can't pass; but on the backstroke, wings separate, feathers turn, and a space is created where air flows through.
I never knew there was less resistance on the backstroke.
If you look up to a bird in flight, watch for that moment when the sun peaks through during the backstroke, that moment when the wind whistles through, the moment of least resistance. A moment brought on by an adaptation to body covering.
No wonder Darwin devoted four chapters to feathers in Descent of Man.