How many species are there within Chamaeza campanisona (Aves, Formicariidae)?

Chamaeza campanisona is a species complex with cryptic diversity and currently has 12 recognized subspecies, predominantly distributed along altitudinal and longitudinal gradients in the Andes. Within the Atlantic Forest, two subspecies are currently recognized. Given the limited taxonomic studies of this genus, we investigated vocal variation among Atlantic Forest populations of this species complex. We analyzed 183 recordings obtained from the Macaulay Library, WikiAves, and Xeno-Canto databases and examined 56 specimens housed at the Museu de Zoologia da Universidade de São Paulo. Vocalizations were analyzed using Raven Pro 1.6.5. Comparisons between populations were made with Multivariate analysis of variance (MANOVA) within the R environment. The following measurements were analyzed: bill height, width and length, tarsus, tail, and wing length. Statistical analysis was not conducted, due to the limited sample size (only one specimen from the northeastern Brazilian population). Plumage coloration was color-coded and compared across specimens. All examined C. campanisona specimens exhibited a distinct black patch on the front, whereas the single specimen from northeastern Brazil lacked this trait. The loudsongs typically consist of rapid series of short-spaced notes, with population-specific variation particularly in pace and in the presence of a terminal series of slowed, descending grunting notes. Our analyses revealed two distinct loudsong patterns: a southern variant occurring from southeastern Paraguay and northeastern Argentina north to Bahia state in Brazil, and a pattern restricted to Ceará state, northeastern Brazil. MANOVA revealed significant differences between populations (p < 0.001). Specifically, song duration varied significantly, whereas maximum entropy differed across populations (p < 0.001). The southern vocal type corresponds to C. campanisona, whereas the northeastern population represents a morphologically and vocally diagnosable unrecognized taxon, which requires formal description once more detailed information on other northeastern specimens is made available.