Another great example of evolutionary wonders in birds is the albatross. They have a tendon sheath that allows them to lock their wings open. This, combined with their giant wingspan, their relative heft (albatrosses are porkers), and some mysterious sensory mechanism and they are able to take advantage of wind gradients to perform a maneuver called "dynamic soaring", wherein the bird extracts energy from the wind. Scientists have measured the heartrate of soaring albatrosses, and found it to be not much higher than their resting heart rate. Albatrosses use this advantage to journey thousands of miles across the pacific, without landing once.
Just to be clear for others: the bird is gaining kinetic energy and/or elevation (potential energy). It's not extracting energy from the wind and converting it to chemical energy (fat/sugar).
Some more info:
https://en.wikipedia.org/wiki/Albatross#Morphology_and_fligh...