They are known as hummingbirds because of the humming sound created by their beating wings, which flap at high frequencies audible to humans. They hover in midair at rapid wingflapping rates, which vary from around 12 beats per second in the largest species, to in excess of 80 in some of the smallest. Of those species that have been measured in wind tunnels, their top speeds exceed 15m/s (54km/h; 34mph) and some species can dive at speeds in excess of 22m/s (79km/h; 49mph).
Hummingbirds have the highest massspecific metabolic rate of any homeothermic animal. To conserve energy when food is scarce, and nightly when not foraging, they can go into torpor, a state similar to hibernation, slowing their metabolic rate to 1/15th of its normal rate.