Fig. 2. Time-resolved vertical aerodynamic force measurements in freely flying hummingbirds and bats in vivo.

(A) A rufous-tailed hummingbird (Amazilia tzacatl) hovers at an artificial feeder, while high-speed cameras record wing kinematics. A mirror below the feeder allows a third perspective of the hovering bird for more accurate 3D reconstruction. A perch (red) instrumented with custom capacitive force sensors measures takeoff and landing forces for accurate weight measurements between each flight. Carbon fiber force plates (blue) mechanically integrate the pressure field generated by the bird and allow us to resolve the instantaneous vertical aerodynamic force. (B) A nectar bat (Glossophaga soricina) hovers in the same aerodynamic force platform but does not drink from the artificial feeder. Full flight recordings from the hummingbird (C) and bat (D) show how body weight is supported by the perch before takeoff and by the aerodynamic force generated with the wings in flight. Hummingbirds landed back on the perch or feeder after each flight, while bats often landed inverted perching on small screw heads on the side walls, which results in zero measured force after the flight. By zooming in to a 0.35-s window, we can see the large downstroke humps and smaller upstroke humps in each wingbeat for hummingbirds (E) and nectar bats (F). Unfiltered forces are shown in light blue and green.