Hummingbirds are birds from the Americas that constitute the family Trochilidae. This bird is the smallest bird in the world. The smallest extant bird species is a hummingbird, the 5 cm (2.0 in) bee hummingbird weighing less than 2.0 g (0.07 oz). They are known as hummingbirds because of the humming sound created by their beating wings which flap at high frequencies audible to humans. Hummingbirds fall into nine main clades, the Topazes, Hermits, Mangoes, Brilliants, Coquettes, Patagona, Mountain Gems, Bees, and Emeralds, defining their relationship to nectar-bearing flowering plants and the birds continued spread into new geographic areas. Now the hummingbird is seen in different places of the earth.