Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm ( ) range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm Bee Hummingbird. They hover in mid-air by rapidly flapping their wings 12–80 times per second (depending on the species). They are known as hummingbirds because of the humming sound created by their beating wings, which sometimes sounds like bees or other insects.