Antbird

The antbird family, Thamnophilidae, consists of over 230 species of passerine birds found across subtropical and tropical regions of Central and South America, ranging from Mexico to Argentina. These birds go by various names, including antshrikes, antwrens, antvireos, fire-eyes, bare-eyes, and bushbirds. Their closest relatives are the antthrushes and antpittas (family Formicariidae), as well as tapaculos, gnateaters, and ovenbirds. Despite what some common names suggest, they are not closely related to true wrens, vireos, or shrikes.

Antbirds are generally small birds with rounded wings and sturdy legs. Their plumage is mostly subdued in shades of grey, white, brown, and rufous, with males and females often differing in color and pattern. Some species flash white patches on their backs or shoulders as warnings to rivals. Most have heavy bills, often hooked at the tip.

The majority of antbirds live in forests, though a few inhabit other environments. Their diet consists mainly of insects and other arthropods, with small vertebrates taken occasionally. Most forage in the understory or midstory, but some feed in the canopy or on the ground. Many join mixed-species feeding flocks, and a few are core members of these groups. Around eighteen species specialize in following army ant swarms to catch the small invertebrates flushed out by the ants, while many others do so opportunistically.

Antbirds are monogamous, mate for life, and defend territories. They typically lay two eggs in a nest that hangs from branches or sits on a branch, stump, or ground mound. Both parents share incubation, brooding, and feeding duties. After the chicks fledge, each parent cares exclusively for one chick.

Thirty-eight species are threatened with extinction due to human activities. Antbirds are not hunted or captured for the pet trade. Their main threat is habitat loss, which leads to fragmentation and increased nest predation in smaller patches.

**Systematics**

The antbird family Thamnophilidae was once considered a subfamily (Thamnophilinae) within the larger Formicariidae, which included antthrushes and antpittas. That larger group was formerly called the "antbird family," with Thamnophilinae referred to as "typical antbirds." In this article, "antbird" and "antbird family" refer to Thamnophilidae.

Thamnophilidae was separated from Formicariidae based on differences in the breastbone and syrinx, as well as DNA–DNA hybridization studies by Sibley and Ahlquist. These antbirds belong to the infraorder Tyrannides (tracheophone suboscines), one of two infraorders in the suborder Tyranni. They are now thought to occupy a fairly basal position within this infraorder, relative to antthrushes, antpittas, tapaculos, gnateaters, and ovenbirds. The sister group of Thamnophilidae is believed to be the gnateaters, while ovenbirds, tapaculos, antthrushes, and antpittas represent a different early branch.

The family contains over 230 species, named antwrens, antvireos, antbirds, and antshrikes based on relative size (increasing in that order, with exceptions), not on any resemblance to true wrens, vireos, or shrikes. Members of the genus *Phlegopsis* are called bare-eyes, *Pyriglena* are fire-eyes, and *Neoctantes* and *Clytoctantes* are bushbirds. Although the family's systematics dates from the mid-19th century, when fewer than half the current species were known, comparisons of myoglobin intron 2, GAPDH intron 11, and mtDNA cytochrome *b* sequences have largely confirmed it. Two major clades exist—one containing most antshrikes and other larger, strong-billed species plus *Herpsilochmus*, and the other containing classical antwrens and more slender, longer-billed species. The monophyly of most genera has been confirmed.

Thamnophilidae includes several large or very large genera and many small or monotypic ones. Some difficult-to-place species appear to form a third, previously unrecognized clade. The results also supported earlier suspicions that some species, especially in *Myrmotherula* and *Myrmeciza*, need to be reassigned to other genera. However, due to the difficulty of sampling such a large number of often poorly known species, the placement of some genera remains uncertain.

**Morphology**

Antbirds range from small to medium-sized passerines. The largest, the giant antshrike, measures 45 cm (18 in) and weighs 150 g (5.29 oz), while the tiny pygmy antwren is just 8 cm (3 in) and weighs 7 g (0.25 oz). Generally, "antshrikes" are relatively large, "antvireos" are medium-sized and stocky, and "antwrens" include most smaller species; "antbird" genera vary greatly in size. Their short, rounded wings allow good maneuverability in dense undergrowth. Legs are large and strong, especially in species that are obligate ant-followers. These birds are well adapted to gripping vertical stems and saplings, which are more common than horizontal branches in the understory, giving them an advantage when following army ant swarms. The claws of ant-following species are longer than those of non-followers, and the soles of some species have tough projections that grip when the foot is clenched. Tarsus length is linked to foraging strategy: longer tarsi are typical in genera like *Thamnophilus* antshrikes, which forage by perch-gleaning.