THAMNOPHILIDAE TYPICAL ANTBIRDS FAUNA PARAGUAY

THAMNOPHILIDAE - TYPICAL ANTBIRDS
Twenty-two species in this exclusively Neotropical family occur in Paraguay. This family was formerly considered a subfamily of a larger Formicariidae, though current thinking is that the two groups may not even be each others closest living relatives. Anatomical differences between the two groups were first noted in the 1960s and these were confirmed by molecular studies at the end of the 20th Century. The current species sequence has remained almost unchanged in over 150 years, but more widespread use of molecular techniques will likely change our perception of relationships in the family. Nest structure and vocal similarities may also be of taxonomic importance.
Morphologically the Antbirds are extremely diverse, ranging from tiny antwrens to the cuckoo-like Giant Antshrike. Superficial similarities to know species at the time, coupled with the habit of "ant-following" shown by some species, led early explorers to attach descriptive names to the groups such as "antshrike" for species with broad, hooked beaks, "antvireo" for stocky, large-headed species with short tails and "antwren" for small, active, long-tailed species with finer bills. Structural features characteristic of the family are not always immediately obvious to the observer and include aspects of tarsal scutellation, connection of the toes, details of the maxilla and certain internal features.
In general antbirds have short, elliptical wings, an adaptation for greater mobility in densely-vegetated habitats. The wings are slotted at the tips giving greater lift and control but sacrificing speed. As a result direct flight is typically slow and fluttery. Most species have proportionately strong legs and large feet, with toes and scales modified for gripping. The bill is large and in "antshrikes" viciously-hooked at the tip. The maxilla is notched, an adaptation for holding and crushing arthropod prey. Tail size is variable, being short in some species and long and graduated in others. Plumage is soft, especially on the back and rump. Many species have a contrastingly coloured interscapular patch (often white) which is hidden at rest but can be revealed during agonistic displays. Elongated crown feathers may be erected into a bushy or spiky crest in many species. The iris is usually dark, but it may be yellow (eg Thamnophilus doliatus) or red (eg Pyriglena). Bill and tarsus colour is relatively uniform throughout the family, varying between blue-grey and black. Plumage is dull, but often attractive, many species possessing black shoulders with rows of white spots. Most species are strongly sexually dimorphic, black and grey dominating in male plumage and brown and buff dominating in females.
Thamnophilids are typical of forested and/or scrubby habitats where they are diurnal in behaviour and roost in dense foliage. Typically the keep to shady areas and rarely emerge into the open. Though elusive in behaviour they are frequently tame when located and may be approached closely. Loafing birds fluff the plumage, particularly on the rump and vent. Head scratching is performed by the indirect method, bringing the foot up over the wing. Excreta is white and fluid, though chitinous insect remains may be regurgitated, rarely being formed into a pellet. Bathing antbirds stand in shallow water with wings and tail partially spread and dip the head and body under water. Canopy species use arboreal water sources, such as the water contained in bromeliads or tree holes. In response to danger many species crouch and freeze. Tail flicking and wing flicking are also used when nervous. The diet consists primarily of arthropods and insect larvae. Larger items may require a substantial handling time before being eaten, being beaten against a branch and having the wings and spines removed. The wings of Lepidopterans are habitually removed. The bill is typically wiped against a branch after feeding. Larger antbirds may take gastropods and small vertebrates, and some also raid nests for eggs. Vegetable matter is occasionally eaten, especially fruit and berries, and the indigestible parts are regurgitated. Prey is usually taken by gleaning, either by reaching upwards from a perch and grabbing with the bill, or following a short fluttery sally to vegetation. Many species habitually investigate dead leaves. Antbirds are regular followers of mixed species flocks, both in the undergrowth and in the canopy.
Antbirds are territorial, sedentary and sing throughout the day. The syringeal structure of antbirds is basic and as a result songs are simple, consisting of a series of similar notes. Typically life-long pair bonds are formed, so the "loud song" of antbirds serves a territorial rather than an advertising function. A "soft song" is given by pairs when they are in close proximity to each other. Most species also possess a harsher, briefer call which is likely used in alarm or to in the presence of perceived danger. Vocalisations are species specific and probably valuable as a taxonomic tool.
In most species courtship feeding is a prelude to mating. Both sexes assist in nest building and there is a break of a few days between the completion of the nest and the laying of the first egg, though additional material maybe added sporadically through the incubation period. Broadly speaking nests fall into two categories, "suspended" (Thamnophilus, Taraba, Herpsilochmus, Formicivora, Cercomacra and Dysithamnus) and "supported" (Myrmorchilus, Pyriglena, Terenura, Batara and Drymophila). The nests of Hypoedaleus and Mackenziaena are unknown. The height at which nests are located corresponds to the foraging height of the species, and Myrmorchilus and Pyriglena may even nest on or near the ground. Eggs are broader at one end than the other and have a white or pinkish ground colour with variable darker spotting or scribbling, concentrated towards the obtuse end. Both sexes incubate the eggs, though it appears that only the female sits at night. The typical incubation period is 14 to 16 days, though it may be a few days longer in larger species. Chicks hatch blind, naked and helpless, the skin colour varying from pink to black. Pin feathers are quickly visible under the skin and they grow rapidly. Both sexes brood and care for the young. Fecal sacs are consumed by the parents in the first few days, later they are carried away from the nest. The nestling period varies greatly from species to species, but typically is short. On leaving the nest the juvenile remains relatively immobile for several days as it gather strength. Pairs will rapidly nest again if they lose their first clutch. Breeding success is low, field experiments suggesting that 10-30% success rate is typical. Brood parasitisim is rare for forest-dwelling species, but may be a problem for species inhabiting scrubby areas. Juveniles probably reach maturity at the end of their first year in most species.

REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Zimmer KJ & Isler ML 2003 - Thamnophilidae Handbook of the Birds of the World Vol 8 - Lynx Ediciones.