Behavior and biomechanics: flapping frequency during tandem and solo flights of cliff swallows.

Aerodynamic models of bird flight, assuming power minimization, predict a quadratic relationship (i.e. U-shaped curve) between flapping frequency and airspeed.

Wind gradient exploitation during foraging flights by black skimmers (Rynchops niger).

Birds commonly exploit environmental features such as columns of rising air and vertical windspeed gradients to lower the cost of flight. These environmental subsidies may be especially important for birds that forage via continuous flight, as seen in black skimmers. These birds forage through a unique behavior, called skimming, where they fly above the water surface with their mandible lowered into the water, catching fish on contact.