Passeriformes

Passeriformes, commonly known as passerines or perching birds, is the largest order of birds, with roughly 5,000 to 6,000 described species in about 60 families. They are distributed worldwide except for many remote polar regions and some isolated oceanic islands, and occupy a broad range of habitats from forests and grasslands to towns and gardens. Passerines are united by their perching-adjusted anisodactyl feet, typically slender bills and a generally compact body shape. Size ranges from small, often less than 10 cm long, to larger species that approach 30 cm.

The order is subdivided into several subgroups. The two largest are Tyranni (suboscines) and Passeri (oscines). A small, basal lineage called Acanthisittae includes the New Zealand wrens and is sometimes treated as a separate suborder within the group. Oscines possess a highly developed syrinx that enables learned vocalizations and complex songs, while suboscines have simpler, more innate calls.

Ecology and behavior vary widely. Passerines feed on insects, seeds, fruit, and nectar, with some specialized foraging in canopies, understory, or ground. Nesting styles range from open-cup nests to cavities, and social systems range from solitary to highly social, often with well-developed territoriality and vocal display. Migration patterns are diverse, with some airborne travelers covering long distances.

Evolutionarily, passerines trace their origin to the Paleogene, with major diversification during the Oligocene to Miocene. Ongoing taxonomic revisions reflect advances in molecular phylogenetics. Many species face threats from habitat loss, invasive predators, and climate change, though some passerines thrive in urban ecosystems.