From NCCR Robotics via IEEE Spectrum:

Birds can dramatically alter the shape and size of their wings because they are composed of an articulated skeleton controlled by muscles and covered with feathers that can overlap. Similarly, the presented drone has a wing equipped with artificial feathers that can be folded to actively change the surface. The wing contains two artificial tendons that can either rotate or straighten the front edge of the wing, thus splaying or storing the feathers. By enabling the drone to reduce its wingspan, the surface area is decreased by 41%, thus significantly reducing drag giving the possibility to fly against strong headwinds. On the other hand, when the wing is fully deployed, the drone can perform turns that are 40% sharper. Since the two foldable wings act independently of each other, the mechanism can also be used to control roll eliminating the need of additional ailerons with advantages in terms of reduced weight and mechanical complexity

Read more and see more from École polytechnique fédérale de Lausanne (EPFL) on YouTube

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