The Sibley–Ahlquist taxonomy is a bird taxonomy proposed by Charles Sibley and Jon E. Ahlquist. It is based on DNA–DNA hybridization studies conducted in the late 1970s and throughout the 1980s.
Traditionally, the bird order Apodiformes contained three living families: the swifts (Apodidae), the treeswifts (Hemiprocnidae), and the hummingbirds (Trochilidae). In the Sibley-Ahlquist taxonomy, this order is raised to a superorder Apodimorphae in which hummingbirds are separated as a new order, Trochiliformes. With nearly 450 species identified to date, they are the most diverse order of birds after the passerines.
Otidae is a clade that includes the superorders Otidimorphae and Strisores. It was identified in 2014 by genome analysis. Earlier it was thought that Strisores was closely related to birds such as pigeons, flamingos, tropicbirds, and the sunbittern and kagu in the taxon Metaves, but subsequent work has provided evidence that Metaves is polyphyletic. Although analyses of genome data provided relatively high support for monophyly of Otidae, indicating that it occupies a basal branch of the clade Passerea, other analyses of large data matrices have not recovered a clade comprising Otidimorphae and Strisores, raising questions about the monophyly of Otidae.
The swifts are a family, Apodidae, of highly aerial birds. They are superficially similar to swallows, but are not closely related to any passerine species. Swifts are placed in the order Apodiformes with hummingbirds. The treeswifts are closely related to the true swifts, but form a separate family, the Hemiprocnidae.
Owlet-nightjars are small crepuscular birds related to the nightjars and frogmouths. Most are native to New Guinea, but some species extend to Australia, the Moluccas, and New Caledonia. A flightless species from New Zealand is extinct. There is a single monotypic family Aegothelidae with the genus Aegotheles.
The frogmouths (Podargidae) are a group of nocturnal birds related to owlet-nightjars, swifts, and hummingbirds. Species in the group are distributed in the Indomalayan and Australasian realms.
The Australian owlet-nightjar is a nocturnal bird found in open woodland across Australia and in southern New Guinea. It is colloquially known as the moth owl. It is the most common nocturnal bird in Australia, and despite suffering from predation and competition by introduced species it is not considered threatened.
The bird genus Apus comprise some of the Old World members of the family Apodidae, commonly known as swifts.
The New Caledonian owlet-nightjar, also known as the enigmatic owlet-nightjar, is a large owlet-nightjar with vermiculated grey-brown and black plumage. It has a long, slightly rounded tail, short, rounded wings, and long, stout legs. Its voice is unknown, but other owlet-nightjar species make churring and whistling sounds. It is the second-largest known owlet-nightjar, much larger than the Australian owlet-nightjar.
The barred owlet-nightjar is a species of bird in the owlet-nightjar family Aegothelidae. It is found in New Guinea. The species was originally thought to be the same species as the Australian owlet-nightjar, until that species was found within the range of the barred owlet-nightjar. It was also considered to be the same species as the Vogelkop owlet-nightjar. There are three subspecies, the nominate, from south-eastern New Guinea, A. b. wiedenfeldi from northern New Guinea, and A. b. plumifer from the D’Entrecasteaux Islands.
Neoaves is a clade that consists of all modern birds with the exception of Palaeognathae and Galloanserae. Almost 95% of the roughly 10,000 known species of extant birds belong to the Neoaves.
Aequornithes, or core water birds, are defined as "the least inclusive clade containing Gaviidae and Phalacrocoracidae".
The order Falconiformes is represented by the extant family Falconidae and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families Cathartidae, Sagittariidae (secretarybird), Pandionidae (ospreys), Accipitridae (hawks) were classified in Falconiformes. A variety of comparative genome analysis published since 2008, however, found that falcons are part of a clade of birds called Australaves, which also includes seriemas, parrots and passerines. Within Australaves falcons are more closely related to the parrot-passerine clade (Psittacopasserae), which together they form the clade Eufalconimorphae. The hawks and vultures occupy a basal branch in the clade Afroaves in their own clade Accipitrimorphae, closer to owls and woodpeckers.
Strisores, sometimes called nightbirds, is a clade of birds that includes the living families and orders Caprimulgidae, Nyctibiidae (potoos), Steatornithidae (oilbirds), Podargidae (frogmouths), Apodiformes, as well as the Aegotheliformes (owlet-nightjars) whose distinctness was only recently realized. The Apodiformes and the Aegotheliformes form the Daedalornithes.
Columbimorphae is a clade discovered by genome analysis that includes birds of the orders Columbiformes, Pterocliformes (sandgrouse), and Mesitornithiformes (mesites). Previous analyses had also recovered this grouping, although the exact relationships differed. Some studies indicated a sister relationship between sandgrouse and pigeons while other studies favored a sister grouping of mesites and sandgrouse instead.
Picodynastornithes is a clade that contains the orders Coraciiformes and Piciformes. This grouping also has current and historical support from molecular and morphological studies.
Vanescaves is a probable clade of strisorean birds that include the clades Steatornithiformes, Nyctibiiformes, Podargiformes (frogmouths), and Apodimorphae. Some molecular studies do support the grouping of these birds, others offer conflicting positions of the non-apodimorphaean strisoreans. In 2019 the authors Chen et al. performed a combined analysis using 2289 ultra-conserved elements [UCEs], 117 morphological characters from extant and fossil taxa found support in this clade. The authors then proposed to name this group, which its meaning is Latin for "vanish birds" in reference to the disparate nature of their geographic distribution, as well as to the poem "A Route of Evanescence" by the American poet Emily Dickinson which features a hummingbird as the main subject. In 2020 Chen & Field named the two major subclades of this group, with Sedentaves and Letornithes for their crown-groups.
Ardei is a suborder of order Pelecaniformes that include the families Ardeidae and Threskiornithidae. Traditionally the ardeids and threskiornithids were classified in the order Ciconiiformes along with Ciconiidae (storks), Phoenicopteridae (flamingos), Scopidae (hamerkop), Balaenicipitidae (shoebill), and even Cathartidae. However, there were some osteological studies that have questioned the monophyly of Ciconiiformes, suggesting that the ardeids and threskiornithids originated from early gruiforms, with the latter being a transitionary taxon to order Charadriiformes. The non-monophyletic nature of Ciconiiformes is supported by recent genomic studies that have found support threskiornithids, ardeids, scopids and balaenicipitids being closely related to Pelecanidae (pelicans).
Pelecanimorphae is a clade of aequornithean birds that comprises the orders Ciconiiformes, Suliformes and Pelecaniformes. In the past the name has been used as a homonym for Pelecaniformes.
Litusilvanae is a proposed clade of birds, position as the sister clade to Aequorlitornithes. This clade comprises Gruimorphae and Strisores. While different lines of evidence from molecular, morphology and the fossil record has found support in the clades Gruimorphae and Strisores Wu et al. (2024) was the first to find support in such a novel sister group relationship between these two taxa.
