The antbirds are a large passerine bird family, Thamnophilidae, found across subtropical and tropical Central and South America, from Mexico to Argentina. There are more than 230 species, known variously as antshrikes, antwrens, antvireos, fire-eyes, bare-eyes and bushbirds. They are related to the antthrushes and antpittas (family Formicariidae), the tapaculos, the gnateaters and the ovenbirds. Despite some species' common names, this family is not closely related to the wrens, vireos or shrikes.

Antbirds are generally small birds with rounded wings and strong legs. They have mostly sombre grey, white, brown and rufous plumage, which is sexually dimorphic in pattern and colouring. Some species communicate warnings to rivals by exposing white feather patches on their backs or shoulders. Most have heavy bills, which in many species are hooked at the tip.

Most species live in forests, although a few are found in other habitats. Insects and other arthropods form the most important part of their diet, although small vertebrates are occasionally taken. Most species feed in the understory and midstory of the forest, although a few feed in the canopy and a few on the ground. Many join mixed-species feeding flocks, and a few species are core members. To various degrees, around eighteen species specialise in following swarms of army ants to eat the small invertebrates flushed by the ants, and many others may feed in this way opportunistically.

Antbirds are monogamous, mate for life, and defend territories. They usually lay two eggs in a nest that is either suspended from branches or supported on a branch, stump, or mound on the ground. Both parents share the tasks of incubation and of brooding and feeding the nestlings. After fledging, each parent cares exclusively for one chick.

Thirty-eight species are threatened with extinction as a result of human activities. Antbirds are not targeted by either hunters or the pet trade. The principal threat is habitat loss, which causes habitat fragmentation and increased nest predation in habitat fragments.

Systematics

The antbird family Thamnophilidae used to be considered a subfamily, Thamnophilinae, within a larger family Formicariidae that included antthrushes and antpittas. Formerly, that larger family was known as the "antbird family" and the Thamnophilinae were "typical antbirds". In this article, "antbird" and "antbird family" refer to the family Thamnophilidae.

Thamnophilidae was removed from Formicariidae, leaving behind the antthrushes and antpittas, due to recognition of differences in the structure of the breastbone (sternum) and syrinx, and Sibley and Ahlquist's examination of DNA–DNA hybridization. In general terms, "antshrikes" are relatively large-bodied birds, "antvireos" are medium-sized and chunky, while "antwrens" include most smaller species; "antbird" genera can vary greatly in size. Members of this family have short rounded wings that provide good manoeuvrability when flying in dense undergrowth. The legs are large and strong, particularly in species that are obligate ant-followers. These species are well adapted to gripping vertical stems and saplings, which are more common than horizontal branches in the undergrowth, and thus the ability to grip them is an advantage for birds following swarms of army ants. The claws of these antbirds are longer than those of species that do not follow ants, and the soles of some species have projections that are tough and gripping when the foot is clenched. Tarsus length in antbirds is related to foraging strategy. Longer tarsi typically occur in genera such as the Thamnophilus antshrikes that forage by perch-gleaning (sitting and leaning forward to snatch insects from the branch), whereas shorter tarsi typically occur in those that catch prey on the wing, such as the Thamnomanes antshrikes. Many species of antbirds have a contrasting 'patch' of white (sometimes other colours) feathers on the back (known as interscapular patches), shoulder or underwing. This is usually concealed by the darker feathers on the back but when the bird is excited or alarmed these feathers can be raised to flash the white patch. dot-winged antwrens puff out white back patches, whereas in bluish-slate antshrikes and white-flanked antwrens the white patch is on the shoulder.

Antbirds are mostly birds of humid lowland rainforests.

Behaviour

Antbirds are diurnal: they feed, breed and defend territories during the day. Many of the family are, however, reluctant to enter areas of direct sunlight where it breaks through the forest canopy. Antbirds will engage in anting, a behaviour in which ants (or other arthropods) are rubbed on the feathers before being discarded or eaten. While many species of antbirds (and other families) may opportunistically feed at army ant swarms, 18 species of antbird are obligate ant-followers, obtaining most of their diet from swarms. Antbirds are neither targeted by the pet trade nor large enough to be hunted; the principal cause of the decline in antbird species is habitat loss. Additionally, new species are discovered at regular intervals; the Caatinga antwren was described in 2000, the acre antshrike in 2004, the sincorá antwren in 2007, and the description of a relative of the Paraná antwren discovered in 2005 in the outskirts of São Paulo is being prepared.

See also

  • List of antbird genera
  • List of antbird species

References

  • Antbird videos and photos on the Internet Bird Collection
  • Xeno-Canto: Antbird sounds