Order-Animalia: Passeriformes

A passerine is any bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or 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 6,500 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 passerines contain several groups of brood parasites such as the viduas, cuckoo-finches, and the cowbirds. Most passerines are omnivorous, while the shrikes are carnivorous.

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.

Anatomy

The foot of a passerine has three toes directed forward and one toe directed backward, called anisodactyl arrangement, and the hind toe (hallux) 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,[7] 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 woodcreeper and treecreepers 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.

Reference: Wikipedia