They are known as hummingbirds because of the humming sound created by their beating wings, which flap at high frequencies audible to other birds and humans. Noted for long beaks, hummingbirds are specialized for feeding on flower nectar, but all species also consume small insects. The smallest is the 5 cm (2.0 in) bee hummingbird, which weighs less than 2.0 g (0.07 oz), and the largest is the 23 cm (9.1 in) giant hummingbird, weighing 18–24 grams (0.63–0.85 oz). Hummingbirds are the smallest mature birds, measuring 7.5–13 cm (3–5 in) in length. Among all birds, male hummingbirds have the widest diversity of plumage color, particularly in blues, greens, and purples. Hummingbirds have varied specialized characteristics to enable rapid, maneuverable flight, exceptional metabolic capacity, adaptations to high altitude, sensitive visual and communication abilities, and long-distance migration in some species. About 28 hummingbird species are listed as endangered or critically endangered, with numerous species declining in population.

With about 366 species and 113 genera, they occur from Alaska to Tierra del Fuego, but most species are found in Central and South America. Hummingbirds are birds native to the Americas and comprise the biological family Trochilidae.

For an alphabetic species list, see List of hummingbird species

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