Hummingbird

Hummingbirds are birds native to the Americas and constitute the biological family Trochilidae. They are the smallest of birds, most species measuring 7.5–13 cm (3–5 in) in length. The smallest extant bird species is the 5 cm (2.0 in) bee hummingbird, which weighs 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. They hover in mid-air at rapid wing-flapping rates, which vary from around 12 beats per second in the largest species, to in excess of 80 in some of the smallest. Of those species that have been measured in wind tunnels, their top speed exceeds 15 m/s (54 km/h; 34 mph) and some species can dive at speeds in excess of 22 m/s (79 km/h; 49 mph). Hummingbirds have the greatest mass-specific metabolic rate of any homeothermic animal. To conserve energy when food is scarce, and nightly when not foraging, they can go into torpor, a state similar to hibernation, slowing metabolic rate to 1/15th of its normal rate. A map of the hummingbird family tree – reconstructed from analysis of 284 of the world's 338 known species – shows rapid diversification from 22 million years ago. 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. While all hummingbirds depend on flower nectar to fuel their high metabolisms and hovering flight, coordinated changes in flower and bill shape stimulated the formation of new species of hummingbirds and plants. Due to this exceptional evolutionary pattern, as many as 140 hummingbird species can coexist in a specific region, such as the Andes range. The hummingbird evolutionary tree shows ancestral hummingbirds splitting from insectivorous swifts (family Apodidae) and treeswifts (family Hemiprocnidae) about 42 million years ago, probably in Eurasia. One key evolutionary factor appears to be an altered taste receptor that enabled hummingbirds to seek nectar. By 22 million years ago the ancestral species of current hummingbirds became established in South America, where environmental conditions stimulated further diversification. The Andes Mountains appear to be a particularly rich environment for hummingbird evolution because diversification occurred simultaneously with mountain uplift over the past 10 million years. Hummingbirds remain in dynamic diversification inhabiting ecological regions across South America, North America, and the Caribbean, indicating an enlarging evolutionary radiation. Within the same geographic region, hummingbird clades co-evolved with nectar-bearing plant clades, affecting mechanisms of pollination. The same is true for the sword-billed hummingbird (Ensifera ensifera), one of the morphologically most extreme species, and one of its main food plant clades (Passiflora section Tacsonia).