A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their toes (three pointing forward and one back), which facilitates perching.
With more than 140 families and some 6,500 identified species, Passeriformes is the largest order of birds and one of the most diverse clades of terrestrial vertebrates, representing 60% of birds. Passerines are divided into three suborders: New Zealand wrens; Suboscines, primarily found in North and South America; and songbirds.
Most passerines are insectivorous or omnivorous, and eat both insects and fruit or seeds.
Etymology
The terms "passerine" and "Passeriformes" are derived from the scientific name of the house sparrow, Passer domesticus, whose genus is the Latin word for sparrow. Formerly this meant the songbirds of Europe; now it also includes perching, non-singing birds from the Americas.
Description
The order is divided into three primary clades: the suborder Tyranni (non-singing, Americas), the suborder Passeri (songbirds or oscines), and the family Acanthisittidae (New Zealand wrens, sometimes considered to constitute a suborder, Acanthisitti). Modern molecular evidence indicates that the New Zealand wrens are sister to the remaining two clades.
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 mimics. The New Zealand wrens are tiny birds restricted to New Zealand, at least in modern times; they were long placed in Passeri.
thumb|right|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 and . 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 and .
Anatomy
The foot of a passerine has three toes directed forward and one toe directed backward, called anisodactyl arrangement. The hind toe (hallux) is long and joins the leg at approximately the same level as the front toes. This arrangement enables passerine birds to easily perch upright on branches. The toes have no webbing or joining, but in some cotingas, the second and third toes are united at their basal third.
The leg of passerine birds contains an additional 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 have 12 tail feathers but the superb lyrebird has 16, and several spinetails in the family Furnariidae have 10, 8, or even 6, as is the case of Des Murs's wiretail. Species adapted to tree trunk climbing such as treecreepers and woodcreeper have stiff tail feathers that are used as props during climbing. Extremely long tails used as sexual ornaments are shown by species in different families. 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 colored 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 parasitic cuckoos, which match the passerine host's egg. The vinous-throated parrotbill has two egg colors, white and blue, to deter 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.
The Passeriformes contain several groups of brood parasites such as the viduas, cuckoo-finches, and the cowbirds.
Bird nest construction is complex and cognitively demanding, and has a very high degree of diversification amongst Passeriformes. A study of brain size and nest construction across a large number of different passerine species indicated that building nests with different attachment modes requires different levels of cognitive abilities.
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. Several more recent fossils from the Oligocene of Europe, such as Wieslochia, Jamna, Resoviaornis, and Crosnoornis, are more complete and definitely represent early passeriforms, and have been found to belong to a variety of modern and extinct lineages.
From the Bathans Formation at the Manuherikia River in Otago, New Zealand, MNZ S42815 (a distal right tarsometatarsus of a tui-sized bird) and several bones of at least one species of saddleback-sized bird have recently been described. These date from the Early to Middle Miocene (Awamoan to Lillburnian, 19–16 mya).
Early European passerines
thumb|upright|[[Wieslochia fossil]]
In Europe, perching birds are not too uncommon in the fossil record from the Oligocene onward, belonging to several lineages:
- Wieslochia (Early Oligocene of Frauenweiler, Germany) – suboscine
- Passeriformes gen. et spp. indet. (Middle Miocene of France and Germany) – basal?
- Passeriformes gen. et sp. indet. (Middle Miocene of Felsőtárkány, Hungary) – oscine?
- Passeriformes gen. et sp. indet. (Late Miocene of Polgárdi, Hungary) – Sylvioidea (Sylviidae? Cettiidae?) 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)<!-- Condor84:240 --> probably belongs to an extant family, most likely passeroidean.