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Alberto Esquivel, Arne Lesterhuis, José Luis Cartes, Rebecca Zarza and Hugo del Castillo and are used with their permission.
RHINOCRYPTIDAE - TAPACULOS
One aberrant species in this exclusively Neotropical family occurs in Paraguay. The Crescentchests Melanopareidae were formerly also placed in this family. The Rhinocryptids are considered the most primitive of the suboscine passerines. The family name Rhinocryptidae means "hidden nose", reference to the bulging lids that cover the nostrils.
Tapaculos are a heterogeneous group of birds when based on external characters alone, making it difficult to generalise. Typically they have a straight, slender and weak bill, strong feet and long claws - the latter an adaptation to a semi-terrestrial existence. The tarsal scaling is taxaspidean and the feathers lack an aftershaft. They have a densely-feathered rump and unique pterylosis of the ventral tract in which the flank element is undivided from the main element. Plumage is dull and moult is highly irregular. Wings are short and rounded with 10 primaries. The rectrices are soft and number 12 - the tail is usually carried cocked. Internally tapaculos have a complex tracheophone syrinx with three pairs of extrinsic and one pair of intrinsic muscles and no pessulus. The processus vocalis is well-developed. Skeletally the metasternum has four notches along the posterior edge and they lack a median keel on the sternum. The species present in Paraguay has advanced skull ossification in adults, a character atypical of the family as a whole. The lachrymal bones are fused with the ectethmoid and the stapes is distinctive. Humerus is non-pneumatic and strongly curved.
Tapaculos are difficult to observe but are very vocal. They are usually encountered in pairs in semi-arid scrubby environments where they frequently call in duet. They are strongly territorial and respond strongly to playback. Their loud voices are innate, being low-pitched so that the noise travels "along the ground". The diet consists mainly of invertebrates which they capture on the ground.
Nests of most Rhinocryptids remain undescribed, but that of the Paraguayan species is well-documented. It is a bulky structure located within 2m of the ground. Eggs are large, rounded, lack sheen and are white in colour. Incubtaion takes 16 to 17 days and the nestling period is 14 to 15 days. Incubation and care of the chicks is shared by both sexes. Chicks hatch naked but soon develop a covering of down. Sexes are alike.
REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Chesser RT 2004 - Molecular Systematics of the New World Suboscine Birds - Molecular Phylogenetics and Evolution 32: p11-24.
Krabbe NK & Schulenberg TS 2003 - Rhinocryptidae Handbook of the Birds of the World Vol 8 - Lynx Ediciones.
