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Description of a new species of bird in the Amazon, the Platyrhynchus or Cryptic Flatbill

Based on an integrative taxonomic approach, ornithologists propose separating the Olive Ridley Flatbill into four distinct species, including the Cryptic Flatbill, which lives in floodplain forests in the Amazon Basin.

The Platyrhynque or Platyrhynque olivâtre, a species which was composed of nine subspecies

Platyrhynchus or Olive Flatbill (Rhynchocyclus olivaceus) near Linhares, in the State of Espírito Santo (Brazil) (click on the photo to enlarge it)
Photo: Hector Bottai / Wikimedia Commons

Genre Rhynchocyclus belongs to the Tyrannidae family, even if Jimmy Gaudin, who has published several articles on taxonomy (read Fluvicolinés: creations of a new genus and a new tribe), recalls that most authors agree in saying that the Rhynchocyclidae should be recognized as a family in their own right. It is currently composed of four species distributed in Central America and northern South America: Platyrhynques or Colombian Flatbills (Rhynchocyclus pacificus), fawn-breasted (R. fulvipectus), olive (R. olivaceus) and short-billed (R. brevirostris). The first two are monotypic, while the other two are polytypic.
The Olive Ridley Flatbill is the one with the largest distribution area. It is divided into nine difficult to distinguish subspecies: they all have a broad head, flattened beak, white eye-ring, olive-green above, greyish-green and yellow-streaked below, dark brown iris, the upper and lower mandibles respectively blackish and white, and the tarsi blue-grey.
The vocal differences are quite clear, and Peter Boesman (2016) proposed dividing them into two groups, the first containing R.o. olivaceus, R.o. guianensis and R.o. sordiddistributed in eastern Amazonia and the Atlantic Forest, and the second R.o. aequinoctialis, R.o. barded, R.o. mirus, R.o. flavus and R.o. jelambianus, living in the western Amazon and the Andes. This classification has not been officially recognized, but it would deserve to be taken into account within the framework of an integrative taxonomic approach combining genetic and vocal analyses.

The methodology followed

The authors analyzed DNA sequences from 99 specimens representing all species of the genus Rhynchocyclusincluding 83 from five subspecies of Olive Ridley Flatbill (R.o. aequinoctialis, R.o. barded, R.o. guianensis, R.o. olivaceus and R.o. sordid). In addition, three samples from two closely related genus species Tolmomyias (T. poliocephalus and T. flaviventris) were taken into account to serve as the basis (root) of the phylogenetic tree.
DNA was extracted from tissue samples, and three mitochondrial and two nuclear genes were amplified. A phylogenetic tree, showing the relationships between species and subspecies, has been developed.
In addition, 133 stuffed specimens were examined, described (colours) and measured (length, height and width of the beak, and lengths of the wing, tarsus and tail). The differences found were subjected to a principal component statistical analysis.
A vocal analysis of 84 recordings of the songs and calls of all Olive Ridley Flatbill subspecies (except R.o. mirror), but also Fawn-breasted, Olive-breasted and Short-billed Flatbills from Colombia, was conducted. Several characteristics were measured: number of notes, total duration of each phrase, frequency peaks of the entire phrase, of the first and last note, and of the delta between them. A statistical analysis of the variance of vocal differences between species and subspecies was conducted.

Recognition of four species

Ranges of four species of flatbills

Distribution areas of (A) Equinoctial Flatbills (R. aequinoctialis), (B) cryptic (R.cryptus), (C) Guyana (R. guianensis) and (E) olive grove (R.s olivaceus).
Map: from Carlynne C. Simões et al

Based on the results of these analyses, the authors propose a new taxonomy of the genus Rhynchocyclus. They suggest dividing Olive Ridley Flatbill into four species with distinct genetic, vocal, and ecological differences, albeit sometimes small:

  • the Olive Ridley Flatbill (R.s olivaceus)
  • the cryptic Flatbill (R.cryptus)
  • the equinoctial or Napo Flatbill (R. aequinoctialis)
  • the Guyana Flatbill (R. guianensis).

The Cryptic Flatbill, a species new to science

The Cryptic Flatbill is a species new to science. As its name suggests, it is very difficult to distinguish by its morphology and its plumage from the other three, but its song (composed of five to eleven rising notes) and its calls (short trills) are distinct.

Listen below to a recording of the song of the Cryptic Flatbill made by Alexander Lees in Brazil on December 9, 2007 (source: Xeno-Canto):

Cryptic Flatbill Habitat

View of the habitat of the Cryptic Flatbill (Rhynchocyclus cryptus): the flooding Amazonian forest or várzea (Click on the image to enlarge)
Photography: Pablo Cerqueira

It is present on the islands of the Amazon River and south of it, reaching the Bolivian department of Cochabamba, and possibly also those of Beni, La Paz and Pando. It lives in floodplain forests (or várzea), including near towns and villages. Its range is vast (more than 700,000 km²), but it is affected by deforestation and the construction of dams. However, it is not threatened.

Guyana and Equinoctial Flatbills, two former subspecies elevated to separate species

The Guyana Flatbill (Rhynchocyclus guianensis) corresponds to the former subspecies R.o. guianensis of the Olive Ridley Flatbill. It lives in Amazonian forests which are never flooded even during strong floods (of the type firm terra), on the Guiana Shields and in the Amazon Basin in northern Peru (west of the Napo River), in southern Ecuador (province of Morona-Santiago) and in central Brazil (south of Amazon River). Genetically distinct, it does not show differences in its plumage, but one of its populations gives a distinct song, formed by a series of 11 to 18 descending and short notes. Further studies may show that other distinct species should be recognized.
The Equinoctial Flatbill (R. aequinoctialis) corresponds to the former subspecies R.o. aequinoctialis of the Olive Ridley Flatbill, also elevated to a separate species on the basis of genetic and vocal criteria. It includes two subspecies: R.a. barded living in the humid forests of northwestern Colombia and Panama, and R.a. aequinoctialispresent in the Ecuadorian Amazon (provinces of Morona-Santiago, Napo and Sucumbios), and possibly also in Peru and Bolivia.

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