Olive-crowned crescentchest

The olive-crowned crescentchest ("Melanopareia maximiliani") is a species of bird in the family Melanopareiidae. It is found in Argentina, Bolivia, and Paraguay.
Taxonomy and systematics.
The crescentchests (genus "Melanopareia") were previously included in family Rhinocryptidae, the tapaculos. A 2010 publication confirmed earlier work and created their present genus. The olive-crowned crescentchest has three subspecies, the nominate "Melanopareia maximiliani maximiliani", "M. m. argentina", and "M. m. pallida". The last has been suggested as a separate species due to vocal differences. In addition, a subpopulation of "M. m. pallida" might be an undescribed taxon.
Description.
The olive-crowned crescentchest is long. Males weigh , one female weighed , and unsexed specimens weighed . The nominate subspecies' crown and upperparts are olive-brown, the throat deep buff, and the chest and belly ochraceous. It has a narrow buff supercilium with a black mask below and a black crescent and chesnut band between the throat and chest. "M. m. argentina" is similar but has paler underparts. "M. m. pallida" is paler still, its throat is more cinnamon than buff, and the facial mask is a lighter black.
Distribution and habitat.
The nominate subspecies of olive-crowned crescentchest is found in La Paz Department of western Bolivia. "M. m. argentina" is found from central Bolivia to northwestern Argentina. "M. m. pallida" is found in southeastern Bolivia, western Paraguay, and northern Argentina. The species generally inhabits dry scrub and grassy areas with small bushes, but "M. m. pallida" also frequents sawgrass in the Chaco Basin. It ranges in elevation mostly from but is found as low as in Argentina.
Behavior.
Feeding.
The olive-crowned crescentchest usually forages alone, but sometimes in pairs, by hopping through dense cover on or near the ground. Its diet has not been recorded.
Breeding.
In Argentina the olive-crowned crescentchest breeds from September to December; an active nest was found in October in central Bolivia. Two nests of "M. m. pallida" were cups of vegetable fiber and palm leaves; they were hidden not far above the ground. One nest of "M. m. argentina" was a tunnel lined with grass. The species' clutch is two or three eggs.
Vocalization.
The nominate olive-crowned crescentchest and "M. m. argentina" have two songs, one described as "chuck" notes and the other as "chi" notes . The song of "M. m. pallida" is faster . The species' call is described as "chit chuck" .
Status.
The IUCN has assessed the oive-crowned crescentchest as being of Least Concern.. It is locally fairly common and in Argentina occurs in several protected areas.