Cercomacra sclateri Hellmayr, 1905 Cercomacra sclateri (partim) Hellmayr, 1905: 288. Formicivora cinerascens (partim) [non Formicivora cinerascens Sclater, 1857] – Sclater (1857: 131). Cercomacra cinerascens (partim) [non Formicivora cinerascens Sclater, 1857] – Sclater (1858: 245). Cercomacra caerulescens (partim) [non Myrmothera caerulescens Vieillot, 1817, non Formicivora caerulescens Ménétriès, 1835] – Pelzeln (1868: 84). Cercomacra cinerascens sclateri – Zimmer (1932: 17). Holotype. AMNH 491022. Male. Type locality. Chyavetas (a misspelling of Chayauitas), E. Peru. Diagnosis. The distinctive loudsong of this taxon consists of raspy-clear one-note phrases, which does not overlap in note duration, pace or the proportion of raspy notes with the other four species. Distribution. This species is limited to the west by the Andes (up to 1067 m, ANSP 11741) and extends east to the left bank of the Ucayali River in southwestern Amazonia. It is found between the Pastaza and Marañon Rivers (on the Ecuador-Peru border) and on the south bank of the latter river, extending south to the Tambo River Valley. Remarks. It can be identified by its darker gray males (very dark gray N / 3) and dark yellow females (olive 5 Y 4 / 4). Morphologically, it differs from C. cinerascens, which is overall lighter. It is also significantly larger than the latter in tail tips and wing chord (females), and in culmen, tail length, and tail tip (males) – with overlapping values (Fig. S 6). Both sexes of this species have white on the inner wing coverts, but this is a variable characteristic found, for example, in individuals from Puerto Yessup, Peru (ANSP 92207), and Teoponte, Bolivia (ANSP 120230). It is absent in individuals collected at the Pithecia Biological Station, south of the Marañon River, in Peru (ANSP 177795). We assume that specimens with an obvious interscapular patch, fimbriae, and wide tail tips collected north of the Marañon River belong to this population because specimens collected north of the Pastaza River but south of the Napo River do not show these features and are identified as C. cinerascens. Likewise, specimen BNHM 89.7-10.540, a female collected in Sarayacu, Ecuador, clearly belongs to C. cinerascens. This suggests that the southern boundary of C. cinerascens is the left bank of the Pastaza River, while the northern boundary of C. sclateri is its right bank. A possible contact zone between these species may exist in the headwaters of the upper Pastaza River.

Published as part of Cavarzere, Vagner, Breviglieri, Enrico L. & Silveira, Luís F., 2026, Integrative taxonomy of the Cercomacra cinerascens species complex with description of two new species (Aves: Thamnophilidae), pp. 73-91 in Vertebrate Zoology 76 on pages 73-91, DOI: 10.3897/vz.76.e171834