Passerine bird family found across subtropical and tropical Central and South America
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. The Thamnophilidae antbirds are members of the infraorder Tyrannides (or tracheophone suboscines), one of two infraorders in the suborder Tyranni. The Thamnophilidae are now thought to occupy a fairly basal position within the infraorder, i. e. with regard to their relatives the antthrushes and antpittas, tapaculos, gnateaters, and also the ovenbirds. The sister group of the Thamnophilidae is thought to be the gnateaters. The ovenbirds, tapaculos, antthrushes and antpittas are thought to represent a different radiation of that early split.
The antbird family contains over 230 species, variously called antwrens, antvireos, antbirds and antshrikes. The names refer to the relative sizes of the birds (increasing in the order given, though with exceptions) rather than any particular resemblance to the true wrens, vireos or shrikes. In addition, members of the genus "Phlegopsis" are known as bare-eyes, "Pyriglena" as fire-eyes and "Neoctantes" and "Clytoctantes" as bushbirds. Although the systematics of the Thamnophilidae is based on studies from the mid-19th century, when fewer than half the present species were known, comparison of the myoglobin intron 2, GAPDH intron 11 and the mtDNA cytochrome "b" DNA sequences has largely confirmed it. There are two major clades – most antshrikes and other larger, strong-billed species as well as "Herpsilochmus", versus the classical antwrens and other more slender, longer-billed species – and the monophyly of most genera was confirmed.
The Thamnophilidae contains several large or very large genera and numerous small or monotypic ones. Several, which are difficult to assign, seem to form a third, hitherto unrecognised clade independently derived from ancestral antbirds. The results also confirmed suspicions of previous researchers that some species, most notably in "Myrmotherula" and "Myrmeciza", need to be assigned to other genera. Still, due to the difficulties of sampling from such a large number of often poorly known species, the assignment of some genera is still awaiting confirmation.
Morphology.
The antbirds are a group of small to medium-sized passerines that range in size from the large giant antshrike, which measures 45 cm (18 in) and weighs 150  g (5.29  oz), to the tiny 8-cm (3 in) pygmy antwren, which weighs 7  g (0.25 oz). 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.
Most antbirds have proportionately large, heavy bills. Several genera of antshrike have a strongly hooked tip to the bill, and all antbirds have a notch or 'tooth' at the tip of the bill which helps in holding and crushing insect prey. The two genera of bushbirds have upturned chisel-like bills.
The plumage of antbirds is soft and not brightly coloured, although it is occasionally striking. The colour palette of most species is blackish shades, whitish shades, rufous, chestnut and brown. Plumages can be uniform in colour or patterned with barring or spots. Sexual dimorphism – differences in plumage colour and pattern between males and females – is common in the family. Overall the pattern within the family is for the males to have combinations of grey, black or white plumage and the females having buff, rufous and brown colours. For example, the male dot-winged antwren is primarily blackish, whereas the female has rust-coloured underparts. In some genera, such as "Myrmotherula", species are better distinguished by female plumage than by male. 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.
Voice.
The songs and calls of antbirds are generally composed of repeated simple uncomplicated notes. The family is one of the suboscines (suborder Tyranni) which have simpler syrinxes ("voiceboxes") than other songbirds. Nevertheless, their songs are distinctive and species-specific, allowing field identification by ear. Antbirds rely on their calls for communication, as is typical of birds in dark forests. Most species have at least two types of call, the "loudsong" and the "softsong". The functions of many calls have been deduced from their context; for example some loudsongs have a territorial purpose and are given when birds meet at the edges of their territories, or during the morning rounds of the territory. Pairs in neighbouring territories judge the proximity of rivals by the degradation of the song caused by interference by the environment. In bouts of territorial defence the male will face off with the other male and the female with her counterpart. Loudsong duets are also potentially related to the maintenance of pair bonds. The functions of softsongs are more complex, and possibly related to pair-bond maintenance. In addition to these two main calls a range of other sounds are made; these include scolding in mobbing of predators. The calls of antbirds are also used interspecifically. Some species of antbirds and even other birds will actively seek out ant-swarms using the calls of some species of ant-followers as clues.
Distribution and habitat.
The distribution of the antbirds is entirely Neotropical, with the vast majority of the species being found in the tropics. A few species reach southern Mexico and northern Argentina. Some species, such as the barred antshrike, have a continental distribution that spans most of the South and Middle American distribution of the family; others, such as the ash-throated antwren, have a tiny distribution.
Antbirds are mostly birds of humid lowland rainforests. Few species are found at higher elevations, with less than 10% of species having ranges above 2000  m (6500 ft) and almost none with ranges above 3000  m (10000 ft). The highest species diversity is found in the Amazon basin, with up to 45 species being found in single locations in sites across Brazil, Colombia, Bolivia and Peru. The number of species drops dramatically towards the further reaches of the family's range; there are only seven species in Mexico, for example. Areas of lower thamnophilid diversity may contain localised endemics, however. The Yapacana antbird, for example, is restricted to the stunted woodlands that grow in areas of nutrient-poor white-sand soil (the so-called Amazonian caatinga) in Brazil, Venezuela and Colombia. Some species are predominantly associated with microhabitats within a greater ecosystem; for example, the bamboo antshrike is predominantly found in bamboo patches.
Genetic comparison of the whole genomes of higher and lower-humidity antbirds have shown some differences in genes linked to water balance and temperature regulation. More significantly, antbirds differ in the regions of the genome that regulate gene activity, suggesting that differences for antbirds are a result less of the genes themselves than of how they are deployed.
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 this has conventionally been considered a way to remove and control feather parasites, it has been suggested that for antbirds it may simply be a way to deal with the distasteful substances in prey items.
Feeding.
The main component of the diet of all antbirds is arthropods. These are mostly insects, including grasshoppers and crickets, cockroaches, praying mantises, stick insects and the larvae of butterflies and moths. In addition antbirds often take spiders, scorpions and centipedes. They swallow smaller prey items quickly, whereas they often beat larger items against branches in order to remove wings and spines. Larger species can kill and consume frogs and lizards as well, but generally these do not form an important part of the diet of this family. Other food items may also be eaten, including fruit, eggs and slugs.
The family uses a number of techniques to obtain prey. The majority of antbirds are arboreal, with most of those feeding in the understory, many in the middle story and some in the canopy. A few species feed in the leaf litter; for example, the wing-banded antbird forages in areas of dense leaf-litter. It does not use its feet to scratch the leaf litter, as do some other birds; instead it uses its long bill to turn over leaves rapidly (never picking them up). The antbirds that forage arboreally show a number of techniques and specialisations. Some species perch-glean, perching on a branch watching for prey and snatching it by reaching forward, where others sally from a perch and snatch prey on the wing. In both cases birds will hop through the foliage or undergrowth and pause, scanning for prey, before pouncing or moving on. The time paused varies, although smaller species tend to be more active and pause for shorter times.
Mixed-species feeding flocks.
Many species participate in mixed-species feeding flocks, forming a large percentage of the participating species within their range. Some of these are core or "nuclear