A passerine is any bird of the orderPasseriformes, which includes more than half of all bird species. Sometimes known as perching birds or – less accurately – as songbirds, passerines are distinguished from other orders of birds by the arrangement of their toes (three pointing forward and one back), which facilitates perching, amongst other features specific to their evolutionary history in Australaves.
With more than 140 families and some 6,600 identified species, Passeriformes is the largest order of birds and among the most diverse orders of terrestrial vertebrates. Passerines are divided into three suborders: Acanthisitti (New Zealand wrens), Tyranni (suboscines) and Passeri (oscines).
The terms "passerine" and "Passeriformes" are derived from the scientific name of the house sparrow, Passer domesticus, and ultimately from the Latin term passer, which refers to sparrows and similar small birds.
The order is divided into three suborders, Tyranni (suboscines), Passeri (oscines), and the basalAcanthisitti. Oscines have the best control of their syrinx muscles among birds, producing a wide range of songs and other vocalizations (though some of them, such as the crows, do not sound musical to human beings); some such as the lyrebird are accomplished imitators. The acanthisittids or New Zealand wrens are tiny birds restricted to New Zealand, at least in modern times; they were long placed in Passeri; their taxonomic position is uncertain, although they seem to be a distinct and very ancient group.
Pterylosis or the feather tracts in a typical passerine
Most passerines are smaller than typical members of other avian orders. The heaviest and altogether largest passerines are the thick-billed raven and the larger races of common raven, each exceeding 1.5 kg (3.3 lb) and 70 cm (28 in). The superb lyrebird and some birds-of-paradise, due to very long tails or tail coverts, are longer overall. The smallest passerine is the short-tailed pygmy tyrant, at 6.5 cm (2.6 in) and 4.2 g (0.15 oz).
The foot of a passerine has three toes directed forward and one toe directed backward, called anisodactyl arrangement. This arrangement enables the passerine birds to perch upon vertical surfaces, such as trees and cliffs. The toes have no webbing or joining, but in some cotingas, the second and third toes are united at their basal third. The hind toe joins the leg at the same level as the front toes. The passeriformes have this toe arrangement in common with hunting birds like eagles and falcons.
The leg arrangement of passerine birds contains a special adaptation for perching. A tendon in the rear of the leg running from the underside of the toes to the muscle behind the tibiotarsus will automatically be pulled and tighten when the leg bends, causing the foot to curl and become stiff when the bird lands on a branch. This enables passerines to sleep while perching without falling off.
Most passerine birds develop 12 tail feathers, although the superb lyrebird has 16. Certain species of passerines have stiff tail feathers, which help the birds balance themselves when perching upon vertical surfaces. Some passerines, specifically in the family Ploceidae, are well known for their elaborate sexual ornaments, including extremely long tails. A well-known example is the long-tailed widowbird.
Eggs and nests
The chicks of passerines are altricial: blind, featherless, and helpless when hatched from their eggs. Hence, the chicks require extensive parental care. Most passerines lay coloured eggs, in contrast with nonpasserines, most of whose eggs are white except in some ground-nesting groups such as Charadriiformes and nightjars, where camouflage is necessary, and in some parasiticcuckoos, which match the passerine host's egg. Vinous-throated parrotbill has two egg colours, white and blue. This can prevent the brood parasitic Common cuckoo.
Clutches vary considerably in size: some larger passerines of Australia such as lyrebirds and scrub-robins lay only a single egg, most smaller passerines in warmer climates lay between two and five, while in the higher latitudes of the Northern Hemisphere, hole-nesting species like tits can lay up to a dozen and other species around five or six.
The family Viduidae do not build their own nests, instead, they lay eggs in other birds' nests.
Origin and evolution
The evolutionary history of the passerine families and the relationships among them remained rather mysterious until the late 20th century. In many cases, passerine families were grouped together on the basis of morphological similarities that, it is now believed, are the result of convergent evolution, not a close genetic relationship. For example, the wrens of the Americas and Eurasia; those of Australia; and those of New Zealand look superficially similar and behave in similar ways, and yet belong to three far-flung branches of the passerine family tree; they are as unrelated as it is possible to be while remaining Passeriformes.
Much research remains to be done, but advances in molecular biology and improved paleobiogeographical data gradually are revealing a clearer picture of passerine origins and evolution that reconciles molecular affinities, the constraints of morphology and the specifics of the fossil record. The first passerines are now thought to have evolved in the Southern Hemisphere in the late Paleocene or early Eocene, around 50 million years ago.
The initial split was between the New Zealand wrens (Acanthisittidae) and all other passerines, and the second split involved the Tyranni (suboscines) and the Passeri (oscines or songbirds). The latter experienced a great radiation of forms out of the Australian continent. A major branch of the Passeri, parvorderPasserida, expanded deep into Eurasia and Africa, where a further explosive radiation of new lineages occurred. This eventually led to three major Passerida lineages comprising about 4,000 species, which in addition to the Corvida and numerous minor lineages make up songbird diversity today. Extensive biogeographical mixing happens, with northern forms returning to the south, southern forms moving north, and so on.
Perching bird osteology, especially of the limb bones, is rather diagnostic. However, the early fossil record is poor because the first Passeriformes were apparently on the small side of the present size range, and their delicate bones did not preserve well. Queensland Museum specimens F20688 (carpometacarpus) and F24685 (tibiotarsus) from Murgon, Queensland, are fossil bone fragments initially assigned to Passeriformes. However, the material is too fragmentary and their affinities have been questioned. Several more recent fossils from the Oligocene of Europe, such as Wieslochia, Jamna, and Resoviaornis, are more complete and definitely represent early passeriforms, although their exact position in the evolutionary tree is not known.
That suboscines expanded much beyond their region of origin is proven by several fossil from Germany such as a broadbill (Eurylaimidae) humerus fragment from the Early Miocene (roughly 20 mya) of Wintershof, Germany, the Late Oligocene carpometacarpus from France listed above, and Wieslochia, among others. Extant Passeri super-families were quite distinct by that time and are known since about 12–13 mya when modern genera were present in the corvoidean and basal songbirds. The modern diversity of Passerida genera is known mostly from the Late Miocene onwards and into the Pliocene (about 10–2 mya). Pleistocene and early Holocenelagerstätten (<1.8 mya) yield numerous extant species, and many yield almost nothing but extant species or their chronospecies and paleosubspecies.
In the Americas, the fossil record is more scant before the Pleistocene, from which several still-existing suboscine families are documented. Apart from the indeterminable MACN-SC-1411 (Pinturas Early/Middle Miocene of Santa Cruz Province, Argentina), an extinct lineage of perching birds has been described from the Late Miocene of California, United States: the Palaeoscinidae with the single genus Palaeoscinis. "Palaeostruthus" eurius (Pliocene of Florida) probably belongs to an extant family, most likely passeroidean.
Systematics and taxonomy
Corvida and Passerida were classified as parvorders in the suborder Passeri; in accord with the usual taxonomic practice, they would probably be ranked as infraorders. As originally envisioned in the Sibley-Ahlquist taxonomy, they contained, respectively, the large superfamilies Corvoidea and Meliphagoidea, as well as minor lineages, and the superfamilies Sylvioidea, Muscicapoidea, and Passeroidea.
The arrangement has been found to be oversimplified by more recent research. Since the mid-2000s, literally, dozens of studies are being published that try rather successfully to resolve the phylogeny of the passeriform radiation. For example, the Corvida in the traditional sense was a rather arbitrary assemblage of early and/or minor lineages of passeriform birds of Old World origin, generally from the region of Australia, New Zealand, and Wallacea. The Passeri, though, can be made monophyletic by moving some families about, but the "clean" three-superfamily-arrangement has turned out to be far more complex and it is uncertain whether future authors will stick to it.
Major "wastebin" families such as the Old World warblers and Old World babblers have turned out to be paraphyletic and are being rearranged. Several taxa turned out to represent highly distinct species-poor lineages, so new families had to be established, some of them – like the stitchbird of New Zealand and the Eurasianbearded reedling – monotypic with only one living species. In the Passeri alone, a number of minor lineages will eventually be recognized as distinct superfamilies. For example, the kinglets constitute a single genus with less than 10 species today but seem to have been among the first perching bird lineages to diverge as the group spread across Eurasia. No particularly close relatives of them have been found among comprehensive studies of the living Passeri, though they might be fairly close to some little-studied tropical Asian groups. Treatment of the nuthatches, wrens, and their closest relatives as a distinct super-family Certhioidea is increasingly considered justified; the same might eventually apply to the tits and their closest relatives.
This process is still continuing. Therefore, the arrangement as presented here is subject to change. However, it should take precedence over unreferenced conflicting treatments in family, genus, and species articles here.
This list is in taxonomic order, placing related families next to one another. The families listed are those recognised by the International Ornithologists' Union (IOC). The order and the division into infraorders, parvorders and superfamilies follows the phylogenetic analysis published by Carl Oliveros and colleagues in 2019.[a] The relationships between the families in the suborder Tyranni (suboscines) were all well determined but some of the nodes in Passeri (oscines) were unclear owing to the rapid splitting of the lineages.
^Oliveros et al (2009) use the list of families published by Dickinson and Christidis in 2014. Oliveros et al include 10 families that are not included on the IOC list. These are not shown here. By contrast, the IOC list includes 6 families that are not present in Dickinson and Christidis. In 5 of these cases, the position of the additional family in the taxonomic order can be determined from the species included by Oliveros and colleagues in their analysis. No species in the family Teretistridae was sampled by Oliveros et al so its position is uncertain.
^The order of the families within the superfamily Orioloidea is uncertain.
^The order of the families within the superfamily Malaconotoidea is uncertain.
^The order of the families within the superfamily Corvoidea is uncertain.
^The taxanomic sequence of the superfamilies, Locustelloidea, Sylvioidea and Aegithaloidea is uncertain, although the order of the families within each of the superfamilies is well determined.
^The order of some of the families within the superfamily Emberizoidea is uncertain.
^The family Teretistridae (Cuban warblers) is tentatively placed here. The family was not included in the analysis published by Oliveros et al (2019). Dickinson and Christidis (2014) considered the genus TeretistrisIncertae sedis. Barker et al (2013) found that Teretistridae is closely related to Zeledoniidae.
^Dyke, Gareth J.; Van Tuinen, Marcel (June 2004). "The evolutionary radiation of modern birds (Neornithes): Reconciling molecules, morphology and the fossil record". Zoological Journal of the Linnean Society. 141 (2): 153–177. doi:10.1111/j.1096-3642.2004.00118.x.
^Mayr, G (2013). "The age of the crown group of passerine birds and its evolutionary significance–molecular calibrations versus the fossil record". Systematics and Biodiversity. 11 (1). doi:10.1080/14772000.2013.765521.
^Distal right humerus, possibly suboscine: Noriega & Chiappe (1991, 1993)
^The former does not even have recognized subspecies, while the latter is one of the most singular birds alive today. Good photos of a bearded reedling are for example hereArchived 16 October 2007 at the Wayback Machine and here.
^ abcdefghijOliveros, C.H.; et al. (2019). "Earth history and the passerine superradiation". Proceedings of the National Academy of Sciences of the United States. 116 (16): 7916–7925. doi:10.1073/pnas.1813206116.
^ abBarker, F.K.; Burns, K.J.; Klicka, J.; Lanyon, S.M.; Lovette, I.J. (2013). "Going to extremes: contrasting rates of diversification in a recent radiation of New World passerine birds". Systematic Biology. 62 (2): 298–320. doi:10.1093/sysbio/sys094.
Hugueney, Marguerite; Berthet, Didier; Bodergat, Anne-Marie; Escuillié, François; Mourer-Chauviré, Cécile & Wattinne, Aurélia (2003). "La limite Oligocène-Miocène en Limagne: changements fauniques chez les mammifères, oiseaux et ostracodes des différents niveaux de Billy-Créchy (Allier, France)" [The Oligocene-Miocene boundary in Limagne: faunal changes in the mammals, birds and ostracods from the different levels of Billy-Créchy (Allier, France)]. Geobios. 36 (6): 719–731. doi:10.1016/j.geobios.2003.01.002.
Roux, T. (2002). "Deux fossiles d'oiseaux de l'Oligocène inférieur du Luberon" [Two bird fossils from the Lower Oligocene of Luberon]. Courrier Scientifique du Parc Naturel Régional du Luberon. 6: 38–57.