Deep in the seasonally flooded savannas of Bolivia, a small olive-green songbird is quietly escaping science. Now, after six decades of confusion and misidentifications, ornithologists have confirmed that the bird is not simply a regional variant of a well-known species of the green genus. Gilophilus but completely new. The discovery adds a new endemic species to South America's already rich bird diversity and highlights how much remains unknown even within well-studied bird families.
Greenlet Benny (Chylophilus moxensis) in a habitat near San Ramon, Beni, Bolivia, January 10, 2024. Note the pale brown-gray auricles combined with dark lores, the dark base of the commissure, the rufous all over the crown and forehead, and the dark irises. Image credit: Tini Vijpkema.
The newly identified species belongs to Gilophilussmall genus of songbirds in the family Vireonidae (vireos, greenfinches and shrikes).
Scientific name Chylophilus moxensis (common name Beni greenback), the bird inhabits the swampy scrubland of the Beni savannas of Bolivia, a vast and ecologically unique region also known as the Llanos de Moxos.
Although this species was first noted by ornithologists back in 1960, it was long thought to be an isolated population of two similar Brazilian species: reddish-crowned green (Gilophilus poicilotis) And grey-eyed greenback (Hylophilus amaurocephalus).
“Morphological differences between many species Gilophilus Greenlet is relatively unimpressive: most are green, gray, yellow and brown,” lead author Dr. Paul van Elsornithologist at the National Museum of Natural History de la Paz, Sauvon and Antus Bolivia, and colleagues explained in their paper.
“In some species, iris color may be one of the most useful features for distinguishing them from similar congeners.”
The uncertainty ended when the authors analyzed one mitochondrial gene and three nuclear genes in the group.
The results showed that the Beni population is not a variant of either known species, but is sister to a clade containing both species. Gilophilus poicilotis And Hylophilus amaurocephalusdiverged approximately 6.6 million years ago.
By comparison, the two previously recognized species diverged from each other much later, around 3.5 million years ago.
Dr van Els and co-authors also carried out detailed analyzes of facial plumage, eye color and vocalizations.
Chylophilus moxensis According to the study, it can be identified diagnostically by the absence of black or brown markings on the ear coverts (a feature consistently present in its relatives), as well as by its uniform dark brown eyes and distinctive song pattern.
Through vocal analysis, the researchers found that the species' song includes “V-shaped notes” and its calls contain harmonics similar to those produced by females. Hylophilus amaurocephalus – a unique combination not inherent in any of the compared species.
Opening Chylophilus moxensis joins the growing list of endemic species known from the Beni savannas.
While the scientists said they “do not believe it is currently at risk”, they also warned that large-scale crop burning poses an acute problem for biodiversity in the area.
“Confession Chylophilus moxensis Because an additional endemic taxon in the region should stimulate efforts to set conservation priorities,” they write in the paper.
“Rampant large-scale agricultural burning is a pressing biodiversity problem in the region.”
“Although we cannot estimate the population Chylophilus moxensis“We do not believe it is currently threatened as suitable habitat is still widespread in the region.”
“However, the relatively low number of records of this species may indicate factors other than lack of observers and may reflect a truly localized phenomenon.”
teams paper was published online on January 1, 2026 in the magazine magazine Bird taxonomy.
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Paul van Els etc.. 2026. A new type of greenlet from Bolivia in Hylophilus poicilotis/amaurocephalus group (Vireonidae). Bird taxonomy 3 (3): 17–37
