Hummingbirds are birds from the Americas that constitute the family Trochilidae. They are among the smallest of birds, most species measuring 7.5–13 cm (3–5 in) in length. Indeed, the smallest extant bird species is a hummingbird, the 5 cm (2.0 in) bee hummingbird weighing less than 2.0 g
Evolution::--- 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.[5] 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.[5][6][7][8]
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
Sexual dimorphisms:::-- Hummingbirds exhibit sexual size dimorphism according to Rensch's rule,[13] in which males are smaller than females in small species, and males are larger than females in large-bodied species.[14] The extent of this sexual size difference varies among clades of hummingbirds.[14][15] For example, the Mellisugini clade exhibits a large size dimorphism, with females being larger than males.[15] Conversely, the Lophomithini clade displays very little size dimorphism; males and females are similar in size.[15] Sexual dimorphisms in bill size and shape are also present between male and female hummingbirds,[15] where in many clades, females have longer, more curved bills favored for accessing nectar from tall flowers.[16] For males and females of the same size, females will tend to have larger bills.[15]
Sexual size and bill differences likely evolved due to constraints imposed by courtship because mating displays of male hummingbirds require complex aerial maneuvers.[13] Males tend to be smaller than females, allowing conservation of energy to forage competitively and participate more frequently in courtship.[13] Thus, sexual selection will favor smaller male hummingbirds
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