Hummingbirds are birds comprising the family Trochilidae. They are among the smallest of birds, and include the smallest extant bird species, the Bee Hummingbirds. They can hover in mid-air by rapidly flapping their wings 12–90 times per second (depending on the species). They can also fly backwards, and are the only group of birds able to do so. Their English name derives from the characteristic hum made by their rapid wing beats. They can fly at speeds exceeding 15 m/s (54 km/h, 34 mi/h).
Hummingbird flight has been studied intensively from an aerodynamic perspective using wind tunnels and high-speed video cameras.
Writing in Nature, the biomechanist Douglas Warrick and coworkers studied the Rufous Hummingbird, Selasphorus rufus, in a wind tunnel using particle image velocimetry techniques and investigated the lift generated on the bird’s upstroke and down-stroke. They concluded that their subjects produced 75% of their weight support during the down-stroke and 25% during the upstroke. Many earlier studies had assumed (implicitly or explicitly) that lift was generated equally during the two phases of the wing-beat cycle, as is the case of insects of a similar size. This finding shows that hummingbirds’ hovering is similar to, but distinct from, that of hovering insects such as the hawk moths.
The Giant Hummingbird’s wings beat at 8–10 beats per second, the wings of medium-sized hummingbirds beat about 20–25 beats per second and the smallest can reach 100 beats per second during courtship displays.
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