The song, the color of its eyes, and the sound produced by its wings are proving to be key factors in allowing a bird that lives in the humid forests of the Sierra Nevada de Santa Marta (SNSM) to move up a taxonomic category and be considered a species exclusive to Colombia.
These details distinguish the ‘Colombian’ guan (the name given to it by researchers) from other related guans with which it shares features such as a long tail, white stripes on the chest, and a patch of intense orange-red skin beneath its bare head.
The ‘Colombian’ guan of the SNSM, together with the ‘argyrotis’, which inhabits Colombia’s main Andes mountain range and the northern mountain ranges of Venezuela, and the ‘albicauda’, which lives in the Perija Mountains in Colombia and Venezuela, constitute three subspecies of the band-tailed guan ‘Penelope argyrotis’, a polytypic species of humid montane forest.
Impressive details studied by researchers
The taxonomic classification of the ‘Colombian’ guan of the SNSM has undergone some changes. In 1912, it was classified as a different species based on its plumage and morphology, and in 1932 it was reclassified as a subspecies of ‘Penelope argyrotis’, a treatment that has been maintained in the main ornithological classifications for almost a century.
However, a recent study published in the journal Ibis proposes that this bird is not a subspecies of ‘Penelope argyrotis’, as it has been considered until now, but rather a distinct species that would exist only in the SNSM.
The details observed by researchers Juan I. Areta, M. Juliana Benitez Saldivar, Pamela C. Rasmussen, and J. V. Remsen Jr. are impressive. They are affiliated with the Institute of Bio and Geosciences of Northwestern Argentina, Louisiana State University, and the Cornell Lab of Ornithology, one of the world’s most prestigious bird research and conservation centers.
They found numerous external diagnostic characteristics distinguishing the ‘argyrotis’ groups (including the subspecies ‘argyrotis’ and ‘albicauda’) from the ‘Colombian’ guan of the SNSM.
‘Argyrotis’ had a dark brown iris, wider, blunt, brown crown feathers, with only those on the forehead partially edged in grayish white, bluish facial skin with conspicuous, bright silvery-white superciliary and malar stripes, and a nape and mantle less extensively marked with pure white lateral edges.
It also had longer wings, less extensive and paler tail tips (‘argyrotis’ cinnamon-colored; ‘albicauda’ dull beige), and dull pink tarsi.
The ‘Colombian’ guan is geographically isolated
By contrast, the ‘Colombian’ guan of the SNSM had a golden ivory iris, thinner, more pointed crown feathers, all edged in grayish white along their entire length, dark gray facial skin with indistinct, dull ash-gray superciliary and malar stripes, a nape and mantle more extensively marked with beige-white lateral edges, shorter wings, more extensive and darker tail tips (reddish chestnut), and brighter red tarsi.
Regarding the dawn song, the researchers found that ‘argyrotis’ produced a series of shorter, more closely spaced (faster), narrower-band rising notes, without frequency jumps (lacking a yodel-like quality), whereas the ‘Colombian’ guan produced a longer series of more widely spaced (slower), broader-band rising notes, with evident frequency jumps (with a yodel-like quality).
Furthermore, the wingbeats of ‘argyrotis’ had two segments separated by a clear pause, while the ‘Colombian’ guan had a single segment. The wingbeats of ‘argyrotis’ had significantly more notes, were significantly longer in both total and net duration, and had a significantly slower gross rate (but not a slower net rate) than those of the ‘Colombian’ guan.
These differences, which the researchers described as “remarkable,” exceed those typically found among taxa currently classified as species within ‘Penelope argyrotis’ and therefore support the recognition of two species: the silver-eared guan ‘Penelope argyrotis’ (with the subspecies ‘argyrotis’ and ‘albicauda’) and the ‘Colombian’ guan of the SNSM.
To document these details, the researchers reviewed 1,471 photographs from the Macaulay Library of the Cornell Lab of Ornithology and 222 recordings from that collection and Xeno-canto, the collaborative platform dedicated to bird songs, as well as museum specimens. Photographs of living birds were key to comparing the iris, skin, and legs, colors that are often lost in preserved specimens.
In addition, the ‘Colombian’ guan is geographically isolated. It remains separated from its relatives by approximately 120 km across the arid part of the Cesar-Rancheria basin. For this reason, the researchers propose recognizing two separate species: the silver-eared guan (‘Penelope argyrotis’, with the subspecies ‘argyrotis’ and ‘albicauda’) and the ‘Colombian’ guan of the SNSM.
The proposal must be evaluated by the South American Classification Committee (SACC) of the American Ornithological Society. If the change is adopted, Colombia would add a new bird species endemic to the Sierra Nevada, where 36 have already been recorded, according to the Alexander von Humboldt Institute.