Hummingbirds belong to the order Apodiformes, meaning, "unfooted birds." There are three families in this order: Trochilidae (hummingbirds), Hemiprocnidae (tree swifts), and Apodidae (swifts). The family Trochilidae belongs to its own Suborder, Trochili. Although the number of genera and species in this group changes continually, currently there are 102 recognized genera and 328 species of hummingbirds. The hummingbird family is divided into two sub-families: Phaethornithinae (hermits) composed of 34 species and a larger group, Trochilinae (trochilines or "typical" hummingbirds), with 294 species.
Hummingbirds feed primarily on the nectar of flowers and supplement their diet with small insects. They have evolved unique characteristics such as narrow elongated beaks, extendable tongues and hovering flight, all of which allow them to exploit nectar resources.
Most hummingbird species are polygynous (males mate with more than one female) and are sexually dimorphic (sexes do not look alike); males (especially trochilines) often have bright iridescent feathers while females have more cryptic coloration. Some male hummingbirds have elaborate ornamentation such as elongated tail feathers and iridescent crests. Male hermits display together in large groups called leks while trochilines are mainly territorial; their courtship often involves dramatic aerial displays.
Known for their small size (the smallest species of hummingbird weighs 2 g), rapid wing movements and heartbeat, hummingbirds can compensate for their high energetic requirements by going into torpor during cold nights. This is especially important for those species found at high elevation where nighttime temperatures can dip below freezing.
Hummingbirds are found in a variety of habitats and while their range includes much of the New World, most hummingbird species are Neotropical.