An anthill long thought to be a single species widespread in the Amazon rainforest is actually several different species. Among them are two recently described species: Cercomacra mura and Cercomacra raucisona – that inhabit separate regions of the southern Amazon. The discovery arose from an exhaustive analysis of museum specimens and vocal recordings of birds in the gray anthill (Cercomacra cinerascens) complex.
Gray antbirds are small, inconspicuous forest birds of the family. Thamnophilidae.
They prefer dense understory habitats and can be found in Brazil, Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname and Venezuela.
Males are typically gray and females brownish, and subtle differences in their plumage made it difficult for ornithologists to distinguish populations across the region’s vast geography.
Reevaluate species limits within the Cercomacra cinerascens At the complex, Paulista State University researcher Vagner Cavarzere and his colleagues compared plumage coloration and body measurements and closely studied the birds’ vocalizations.
They examined 682 bird specimens from museum collections and analyzed 347 recordings of their songs.
They also used BirdNET, a deep learning system trained to classify bird sounds, to analyze the structure of the songs.
“Birds rely heavily on vocal communication, which is important for species recognition,” the researchers said.
“Their songs act as acoustic signatures, providing a powerful key to unlocking hidden diversity.”
The results revealed clear divisions between populations separated by the main Amazonian rivers.
Birds north of the Pastaza, Marañón, Solimões and Amazonas rivers consistently differed in coloration and song patterns from southern populations.
Cercomacra mura It inhabits the forest region between the Ucayali and Madeira rivers, while Cercomacra raucisona It lives between the Madeira and Tapajós rivers.
“These rivers function as long-term natural barriers,” the researchers said.
“Populations diverged independently over millennia into the unique species we describe today, which are kept isolated by these large rivers.”
Scientists also recognized several previously named forms as full species, bringing the total number of species in the complex to five.
They concluded that each has distinct vocal characteristics and geographic ranges, with little evidence of overlap or hybridization.
The discovery underscores how much of the Amazon’s biodiversity still remains to be clarified, even among birds that scientists thought they already understood well.
“By fusing artificial intelligence with the fundamental science of bioacoustics and museum collections, we can uncover diversity that would otherwise remain invisible,” the authors said.
“Recognizing these species is the first and most critical step in ensuring their protection in a rapidly changing world.”
The discovery is described in a new paper in the diary Vertebrate zoology.
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V. Cavarzere et al. 2026. Integrative taxonomy of Cercomacra cinerascens species complex with description of two new species (Aves: Thamnophilidae). Vertebrate zoology 76: 73-91; doi:10.3897/vz.76.e171834