FORMICARIIDAE GROUND ANTBIRDS FAUNA PARAGUAY

FORMICARIIDAE - GROUND ANTBIRDS

Three species in this exclusively Neotropical family occurs in Paraguay, each classified in its own genus. Until recently this family also included the "True Antbirds" Thamnophilidae, but DNA-DNA hybridisation analysis suggests that the two families are rather more distantly related than previously thought and that the Ground Antbirds are actually closer to the Furnarids than the Thamnophilids. The Formicariidae and Thamnophilidae apparently do not share chewing lice or nematode parasites. The use of the name "antbird" is a hangover from the days when Formicariidae included Thamnophilidae - they do not in fact follow ants. The characteristics of the three genera found in Paraguay are given below.
Ground Antbirds have a large head, big eyes, long legs and a stubby tail. They are poor flyers, lacking a sternal keel and having short, rounded wings - in fact some species are almost flightless. There are 10 primaries and 10 to 12 rectrices. Plumage is dull and vocalisations play the signalling role. Paraguayan species exhibit no sexual dimorphism. Internally the syrinx lacks intrinsic muscles and has three pairs of extrinsic muscles. The processus vocalis is well-developed and sternotracheal extrinsic muscle is simple.
Ground Antbirds are sedentary inhabitants of the lower strata of dense humid forest. They forage on the ground, but many sing from a branch. All species are frequently heard, but difficult to observe and may freeze for long periods if disturbed. They appear to be quite aggressive against conspecifics, though most territorial conflicts are settled vocally. Voices are loud, characteristic, have a ventriloqual quality but are easily-imitated. Songs are most often heard at dawn and dusk, and in Paraguayan species it is only the male that sings. Feeding is a solitary pursuit, usually under dense cover, though they may emerge into more open situations at dawn and dusk. Invertebrates form the bulk of the diet. They do not join mixed species flocks.
Breeding behaviour is little known because of the secrecy of these birds. Two eggs, large for the size of the bird, form the typical clutch. Hatchlings are dark-skinned and naked in known species.

Chamaeza (1 species). Antthrush. Bill short and weak. Reduced rictal bristles. Two rows of scutes on posterior side of tarsus. Metasternum with two notches on posterior margin. Walks deliberately with horizontal body and tail pumping. May sing from the ground or from a perch. Forages by walking slowly and deliberately and flicking leaves with the bill. Eggs almost spherical. Incubation by both sexes.

Grallaria (1 species). Large antpitta with heavy, prominently-curved bill. Long rictal bristles. One row of scutes on posterior side of tarsus. Metasternum with two notches on posterior margin. Vertical stance and hopping gait, rarely cocks tail. Makes bobbing movements and regularly flicks wings. Fluffs throat and throws head back when singing, usually from a perch. Forages by hopping and pattering and capturing prey that they disturb. Eggs somewhat rounded. Incubation by female only.

Hylopezus (1 species). Small antpitta with straight, strong bill. Lack rictal bristles. Fused or nearly fused tarsal scutes. Metasternum with four notches on posterior margin. Vertical stance and hopping gait, rarely cocks tail. Makes bobbing movements and regularly flicks wings. Fluffs throat and throws head back when singing, usually from a perch. Forages by hopping and pattering and capturing prey that they disturb. Eggs somewhat rounded. Incubation by both sexes.

REFERENCES
Krabbe NK & Schulenberg TS 2003 - Formicariidae Handbook of the Birds of the World Vol 8 - Lynx Ediciones.