Perching birds (Passeriformes), also known as passerines, are the most diverse of all living bird groups. Perching birds include tits, sparrows, finches, wrens, dippers, thrushes, starlings, warblers, crows, jays, wagtails, swallows, larks, martins, warblers and many others. The estimated 5,500 living species of perching birds account for more than half of all bird species alive today.
Perching birds have a unique foot structure that enables them to grip onto thin branches, twigs, slender reeds and flimsy grass stems. Some species can even grasp vertical surfaces with ease, such as rock faces and tree trunks.
Their foot consists of four long, thin toes. Three toes face forward and one faces backwards. This arrangement of the toes is referred to as an anisodactyl arrangement. There is no webbing that joins the toes.
Perching birds can move each toe independently of the others and the back-facing toe is particularly strong, enabling a tight grip. The foot is structured such that when the bird lands on a branch, its weight causes its leg tendons to pinch and tighten. As a result, the foot clamps snugly around the branch. This secure grasp enables perching birds to hold tightly to their perch even when they sleep.
In addition to their unique foot structure, perching birds are also notable for their ability to sing complex songs. Their voicebox (also called a syrinx) is a vocal organ located in their trachea. Although perching birds are not the only group of birds to have a syrinx, the syrinx is most highly-developed in perching birds. Each species of perching birds sings a unique song. Some songs are simple while others are long and complex. Species with the most lyrical songs include thrushes, wrens, larks, nightingales and lyrebirds.
Some perching birds must learn their songs from their parents while other perching birds have the innate ability to sing their song (the tune is already hard-wired so they do not need to learn their song from their parents).
Most perching birds form monogamous pair bonds during the breeding season. They establish a territory inside which they build a nest and raise their young. Passerines provide their young with a good deal of parental care. Chicks are born blind and without feathers and thus emerge from the egg quite helpless.
Perching birds vary widely in their appearance. Most members of the group are small in size. The largest members of the group are the crows and ravens which can grow to 25 inches in length. The smallest members of the group are the short-tailed pygmy tyrants which measure a mere 3 inches in length.
Perching birds also exhibit a variety of bill shapes and sizes when compared among species. These different bill shapes are often reflective of the particular diet a species feeds on. For example, species that feed on seeds often have a short, conical bill. Species that feed on insects have a thinner, dagger-like bill. Nectar-feeders such as the sunbird, have long thin bills that are curved downwards, enabling them to extract nectar from flowers.
Plumage color and pattern is highly variable among perching birds. Some species are dull in color and markings while others have bright or ornamental feathers. Plumage also varies between the sexes in some species of perching birds, with males often having more vividly colored plumage and females exhibiting a subdued palette.
Perching birds feed primarily on energy-rich foods such as seeds or invertebrates. A few species also feed on nectar and fruits.
Perching birds are divided into three basic groups, the New Zealand wrens (Acanthisitti), the suboscines (Tyranni) and the oscines (Passeri).