Deep within Bolivia’s seasonally flooded savannah, a small olive-green songbird has eluded scientific classification for decades. After 60 years of misidentification, ornithologists have finally confirmed that this bird is not merely a regional variant within the genus Hylophilus. It represents a completely new species. This discovery adds to South America’s rich avian diversity and underscores the vast unknowns still present within even well-studied bird families.

The newly identified species belongs to the Hylophilus genus, part of the Vireonidae family, which includes vireos, greenlets, and shrikes.

With the scientific name Hylophilus moxensis (common name: Beni Greenlet), this bird thrives in the wet scrublands of Bolivia’s Beni Savannah, an ecologically unique area also known as Llanos de Moxos.

The species was first noted by ornithologists in 1960 but was initially thought to be an isolated population of two similar species found in Brazil: the Rufous-Clown Greenlet (Hylophilus poirotis) and the Gray Greenlet (Hylophilus amaurocephalus).

“Morphological differences among many Hylophilus Greenlet species are subtle. Most display shades of green, gray, yellow, and brown,” explains Dr. Paul Van Els, an ornithologist at the National Museum of History in La Paz, Bolivia. He and his colleagues detailed their findings in a recent paper.

“For certain species, iris color is one of the most effective traits to differentiate them from similarly appearing relatives.”

By analyzing one mitochondrial and three nuclear genes, the research team clarified the uncertainty surrounding this population.

Results revealed that the Beni population is distinct from known species and is more closely related to Hylophilus poirotis and Hylophilus amaurocephalus, which diverged approximately 6.6 million years ago.

In contrast, the latter two species separated from one another about 3.5 million years ago.

Van Els and his team also conducted comprehensive analyses of facial plumage, eye color, and vocalizations.

Research indicates that the Hylophilus moxensis can be uniquely identified by the absence of black or brown markings behind the ears, a trait consistently found in closely related species, along with uniformly dark brown eyes and a distinctive vocal pattern.

In vocal studies, researchers observed that this species’ calls feature “V-shaped notes,” and their vocalizations include overtones reminiscent of female Hylophilus amaurocephalus calls—a unique combination not shared with either comparative species.

The discovery of Hylophilus moxensis contributes to a growing list of endemic species found in the Beni savannah.

While scientists currently do not regard this species as threatened with extinction, they caution that extensive agricultural burning poses significant threats to the region’s biodiversity.

“Recognizing Hylophilus moxensis should enhance conservation priorities in this area,” the authors noted.

“Rampant agricultural burning poses a serious risk to the region’s biodiversity.”

“Though we cannot accurately estimate the population size of Hylophilus moxensis, we do not currently consider it at risk of extinction, as there remains extensive suitable habitat.”

“However, the relatively low number of sightings might indicate issues beyond mere observer rarity, potentially reflecting a truly localized population.”

The team’s paper was published online on January 1, 2026, in the journal Bird Systematics.

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Paul Van Els et al. 2026. A new species of greenlet from Bolivia: Hylophilus moxensis (Vireonidae). Bird Systematics, 3(3):17-37