hummingbird

Hummingbirds are birds native to the Americas and comprise the biological family Trochilidae. With about 361 species and 113 genera, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropics around the equator. They are small birds, with most species measuring in length. The smallest extant hummingbird species is the bee hummingbird, which weighs less than . The largest hummingbird species is the giant hummingbird, weighing . They are specialized for feeding on flower nectar, but all species also consume flying insects or spiders.

Hummingbirds split from their sister group, the swifts and treeswifts, around 42 million years ago. The common ancestor of extant hummingbirds is estimated to have lived 22 million years ago in South America. 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 mid-air at rapid wing-flapping rates, which vary from around 12 beats per second in the largest species to around 80 per second in small hummingbirds. Of those species that have been measured during flying in wind tunnels, their top speeds exceed . During courtship, some male species dive from of height above a female at speeds around .

Hummingbirds have the highest mass-specific metabolic rate of any homeothermic animal. To conserve energy when food is scarce and at night when not foraging, they can enter torpor, a state similar to hibernation, and slow their metabolic rate to 1/15 of its normal rate.

Taxonomy and systematics

The family Trochilidae was introduced in 1825 by Irish zoologist Nicholas Aylward Vigors with ''Trochilus'' as the type genus. Molecular phylogenetic studies of the hummingbirds have shown that the family is composed of nine major clades. When Edward Dickinson and James Van Remsen Jr. updated the '' Howard and Moore Complete Checklist of the Birds of the World'' for the 4th edition in 2013, they divided the hummingbirds into six subfamilies.

Molecular phylogenetic studies determined the relationships between the major groups of hummingbirds. In the cladogram below, the English names are those introduced in 1997. The Latin names are those introduced in 2013.

In traditional taxonomy, hummingbirds are placed in the order Apodiformes, which also contains the swifts, but some taxonomists have separated them into their own order, the Trochiliformes. Hummingbirds' wing bones are hollow and fragile, making fossilization difficult and leaving their evolutionary history poorly documented. Though scientists theorize that hummingbirds originated in South America, where species diversity is greatest, possible ancestors of extant hummingbirds may have lived in parts of Europe and what is southern Russia today.

Around 360 hummingbirds have been described. They have been traditionally divided into two subfamilies: the hermits (subfamily Phaethornithinae) and the typical hummingbirds (subfamily Trochilinae, all the others). Molecular phylogenetic studies have shown, though, that the hermits are sister to the topazes, making the former definition of the Trochilinae not monophyletic. The hummingbirds form nine major clades: the topazes and jacobins, the hermits, the mangoes, the coquettes, the brilliants, the giant hummingbird (''Patagona gigas''), the mountaingems, the bees, and the emeralds. The topazes and jacobins combined have the oldest split with the rest of the hummingbirds. The hummingbird family has the third-greatest number of species of any bird family (after the tyrant flycatchers and the tanagers).

Fossil hummingbirds are known from the Pleistocene of Brazil and the Bahamas, but neither has yet been scientifically described, and fossils and subfossils of a few extant species are known. Until recently, older fossils had not been securely identifiable as those of hummingbirds.

In 2004, Gerald Mayr identified two 30-million-year-old hummingbird fossils. The fossils of this primitive hummingbird species, named '' Eurotrochilus inexpectatus'' ("unexpected European hummingbird"), had been sitting in a museum drawer in Stuttgart; they had been unearthed in a clay pit at Wiesloch–Frauenweiler, south of Heidelberg, Germany