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Tropicbirds are a family, Phaethontidae, of tropical pelagic seabirds now classified in their own order Phaethontiformes. Their relationship to other living birds is unclear, and they appear to have no close relatives. There are three species in one genus, ''Phaethon''. They have predominantly white plumage with elongated tail feathers and small feeble legs and feet. ==Taxonomy, systematics and evolution== Tropicbirds were traditionally grouped in the order Pelecaniformes, which contained the pelicans, cormorants and shags, darters, gannets and boobies and frigatebirds; in the Sibley-Ahlquist taxonomy, the Pelecaniformes were united with other groups into a large "Ciconiiformes". More recently this grouping has been found to be massively paraphyletic (missing closer relatives of its distantly related groups) and split again. Microscopic analysis of eggshell structure by Konstantin Mikhailov in 1995 found that the eggshells of tropicbirds lacked the covering of thick microglobular material of other Pelecaniformes. Recent research suggests that the Pelecaniformes as traditionally defined are paraphyletic too. The tropicbirds and the related prehistoric family Prophaethontidae are considered a distinct order, Phaethontiformes, not closely related to any other living birds. Some early studies in the last decade suggested a distant relationship to Procellariiformes, but since 2004 they have been placed in Metaves, or in a lineage with no affinities with Procellariiformes, by the results of most recent molecular studies.〔Naish, D. (2012). "Birds." Pp. 379-423 in Brett-Surman, M.K., Holtz, T.R., and Farlow, J. O. (eds.), ''The Complete Dinosaur (Second Edition)''. Indiana University Press (Bloomington & Indianapolis).〕 Jarvis, ''et al''.'s 2014 paper "Whole-genome analyses resolve early branches in the tree of life of modern birds" aligns the tropicbirds most closely with the sunbittern and the kagu of the Eurypygiformes, with these two clades forming the sister group of the "core water birds", the Aequornithes, and the Metaves hypothesis abandoned. Family Phaethontidae * Genus ''Phaethon'' * * Red-billed tropicbird ''Phaethon aethereus'' (tropical Atlantic, eastern Pacific, and Indian oceans) * * Red-tailed tropicbird, ''P. rubricauda'' (Indian Ocean and the western and central tropical Pacific) * * White-tailed tropicbird, ''P. lepturus'' (widespread in tropical waters, except in the eastern Pacific) Within the group, the red-tailed and white tailed are each other's closest relatives, with the red-billed a sister taxon of that group. ''Phaethusavis'' and ''Heliadornis'' are prehistoric genera of tropicbirds described from fossils. ==Description== Tropicbirds range in size from 76 cm to 102 cm in length and 94 cm to 112 cm in wingspan. Their plumage is predominantly white, with elongated central tail feathers. The three species have different combinations of black markings on the face, back, and wings. Their bills are large, powerful and slightly decurved. Their heads are large and their necks are short and thick. They have totipalmate feet (that is, all four toes are connected by a web). The legs of a tropicbird are located far back on their body, making walking impossible, so that they can only move on land by pushing themselves forward with their feet.〔 The tropicbirds' call is typically a loud, piercing, shrill, but grating whistle, or crackle. These are often given in a rapid series when they are in a display flight at the colony. In old literature they were referred to as boatswain (bo'sun'/bosun) birds due their loud whistling calls. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tropicbird」の詳細全文を読む スポンサード リンク
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