Taxonomy: A highly debated form in science. Berlioz (1959) described Serpophaga griseiceps based on four specimens from Cochabamba, Bolivia. Traylor (1979, 1982) considers S. griseiceps as juveniles of S. munda, and Remsen and Traylor (1989) confirmed this. Straneck (1993) revalidates S. griseiceps for a taxon found in Argentina that does not vocalize like S. "munda" nor like S. subcristata. Herzog and Mazar Barnett (2004) mention that Straneck’s (1993) work has methodological issues, claiming that Berlioz’s (1959) specimens of S. griseiceps represent juveniles of S. munda and Straneck’s S. griseiceps specimens are apparently a cryptic species of Serpophaga previously undescribed. Straneck (2007) describes a new species named Serpophaga griseicapilla for the “Straneck’s S. griseiceps” specimens, detailing that the error of authors insisting that S. griseiceps are juveniles of S. munda comes from their studies being based only on skins and not on acoustic analyses of the species, clarifying that such studies of the populations in Bolivia are needed to clarify S. griseiceps from Berlioz (1959). Furthermore, he adds that in the north and west of Argentina, specimens of S. griseicapilla with very little yellow ventral or simply white ventral and subcaudal regions have been observed, which coincides with the behavior of the subspecies of S. subcristata, where the more arid the region, the less coloration they possess.

Comparison with the Common Piojito (Serpophaga subcristata): Twin species that are very difficult to differentiate in photographs. The Trinador Piojito has a uniform gray-brown crown, almost without white. Adults have some black feathers with a white base on the crown, though the white is mostly covered and not visible, never having as much white on the crown as the Common Piojito. The size is smaller than that of the Common Piojito.

Vocalization: It is distinguishable from the Common Piojito by its acoustic repertoire, which they repeat throughout the year, although more frequently during the breeding period. It is worth noting that some calls of the Common Piojito could be considered trills, which could confuse people who do not know in detail the characteristic vocalization of the Trinador Piojito, meaning that not only the Trinador Piojito "trills".

Geographic Distribution: Breeds sympatrically with S. s. munda (the western subspecies of the Common Piojito) from Chubut to Salta in the arid region of central and western Argentina, from the north of Chubut Province, the Andean foothills of Mendoza, San Juan, Catamarca, La Rioja, Tucumán, Salta, and Jujuy; central and eastern Río Negro, central and western La Pampa, central and western Córdoba and Santiago del Estero, western Chaco, and Formosa.

Migration: Coexists with S. s. subcristata (the eastern subspecies of the Common Piojito) only during the autumn-winter period, when it migrates longitudinally toward the east of Formosa, east of Córdoba, and east of Santiago del Estero, Buenos Aires, Entre Ríos, Santa Fe, Corrientes, Chaco, Misiones. It eventually reaches Paraguay, Brazil, and Uruguay.

Behavior: The behavior of the Trinador Piojito and Common Piojito is similar, hopping and fluttering short distances on tree branches to catch small arthropods, so behavioral differences are not considered valid until more studies on this genus are published.

Author of this compilation: Jorge La Grotteria - 04/05/2016

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