The Antbird

May 08, 2011 Features / Columnists, Interesting Creatures in Guyana

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Antbirds are of a large family called Thamnophilidae, of passerine birds found across subtropical and tropical Central and South America ranging from Mexico to Argentina. There are more than 200 species, known variously as antshrikes, antwrens, antvireos, fire-eyes, bare-eyes and bushbirds.
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. Several are also known to 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.
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
To various degrees, around eighteen species specialise in following columns of army ants to eat the small invertebrates flushed by the ants, and many others may feed in this way opportunistically, a practice from which the name antbird is derives.
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.
This bird species is said to be 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 due to 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.
Antbirds are diurnal, feeding, breeding and defending territories during the day. Many of the family are, however, reluctant to enter direct sunlight where it breaks through the canopy. Antbirds will engage in anting, a behaviour where 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.
The songs and calls of antbirds are generally composed of repeated simple uncomplicated notes. 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 potential 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.

(Source: Wikipedia – The Free Online Encyclopedia)

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