Perching Birds

The order Passeriformes contains perching birds, which are often called passerines. This large and diverse order of over 70 families accounts for well over half the bird species of the world; it contains many rapidly evolving groups with large numbers of related species. Because the evolution of passerines has been rapid and relatively recent and because of their relatively small stature, the fossil record has shed little light on our understanding of passerine relationships.

Passerines fill a diversity of ecological roles. There are aerial insect eaters such as swallows; bark gleaners such as woodcreepers and nuthatches; heavy-billed seed eaters such as finches, sparrows, and grosbeaks; and hook-billed predators such as shrikes. In addition there are nectar specialists, flycatchers, foliage gleaners, and even aquatic forms (the dippers). Despite this remarkable ecological diversity, passerines share a number of anatomical characteristics. The most notable characteristic is the perching foot -- three toes point forward and one, known as the hallux, points backward at the same level.

Major divisions in this order are oscines and suboscines. The suboscines group includes families of tyrant flycatchers, antbirds, ovenbirds, woodcreepers, and other smaller families -- diverse components of the avifauna of the New World tropics.

Oscines, or songbirds, represent the vast majority of familiar temperate-zone land birds. Experts are continually studying the relationships of the families within this group with increasing sophisticated techniques. The oscines are exceedingly diverse, but several major lineages have been identified. One giant assemblage, which is especially diverse in the Old World, is comprised of thrushes and their relatives, which most taxonomists place in the family Muscicaoidae. Another large lineage which is most diverse in the New World, consists of such groups as wood warblers, tanagers, cardinals, grosbeaks, bunting and New World blackbirds and orioles. These birds have only nine primary feathers on each wing instead of ten and are members of the Emberizidae family.