Any perching bird.
All passerines belong to the largest order of birds, Passeriformes, and have feet specialized for holding onto a horizontal branch (perching). The passerine foot has three forward-directed toes and one backward-directed toe. Most passerines have moderately curved, sharp claws. Some ground-dwelling species (e.g., larks , pipits ) have flatter, longer feet. Species that spend much time airborne (e.g., swallows ) have small, weak feet. Species that cling and climb (e.g., nuthatches ) have strong, sharp, curved claws. Passerines include about 4,000 species of oscines ( songbirds ; suborder Passere, or Oscines) and 1,100 species of suboscines (suborders Eurylaimi, called broadbills; Tyranni, including flycatchers ; and Menurae, including lyrebirds ). Suboscines lack the syrinx of the songbirds or have only a poorly developed one, but some can utter complex vocalizations. All passerines are land birds, abundant worldwide except in Antarctica. Most are insectivorous, solitary nesters that build a cup-shaped open nest.