A newly identified bird species, the Beni greenlet (Hylophilus moxensis), has been officially recognized by ornithologists after decades of misidentification. Published in the journal Avian Systematics on January 1, 2026, the discovery highlights the continued richness of South American avifauna and the complexity of distinguishing closely related species, especially within well-studied groups like the Hylophilus greenlets.
A Bird Hiding In Plain Sight For Over 60 Years
For more than six decades, the small olive-green bird spotted near San Ramón in Bolivia’s Beni savannas was mistakenly classified as a variant of already known species, either the rufous-crowned greenlet (Hylophilus poicilotis) or the gray-eyed greenlet (Hylophilus amaurocephalus). But new genetic and morphological analyses have revealed its true identity as a distinct species.
Researchers used both mitochondrial and nuclear gene sequencing to build a clearer phylogenetic picture. The results were conclusive: Hylophilus moxensis split from its nearest relatives approximately 6.6 million years ago, a far earlier divergence than previously thought. In contrast, the two known Brazilian species diverged around 3.5 million years ago. This evolutionary distance, paired with specific physical and vocal traits, cemented the greenlet’s status as a separate species.
“Morphological variation between many species of Hylophilus greenlet is relatively underwhelming: most are green, gray, yellow, and brown,” explained Dr. Paul van Els, lead author and ornithologist at the Museo Nacional de Historia Natural de la Paz, Sovon, and Anthus Bolivia. “In some species, iris color may be one of the most useful characters to separate them from similar-looking congeners.”
What Makes Hylophilus Moxensis Unique
Field observations identified several key features that distinguish Hylophilus moxensis from its close relatives. The bird has pale brownish-gray auriculars, dark lores, a rufous crown and frons, and uniformly dark irides, or eyes. Unlike its cousins, it lacks the black or brown markings typically seen on the ear coverts of other Hylophilus species.
Vocalizations also played a crucial role in its identification. The new species exhibits “V-shaped notes” in its songs and calls with harmonics similar to those produced by female H. amaurocephalus, creating a distinctive acoustic signature.
These findings were detailed in the Avian Systematics study, reinforcing how subtle differences, once dismissed, can reveal major taxonomic insights when subjected to modern techniques. The study showcases how both genetics and bioacoustics are reshaping the taxonomy of even familiar bird groups.
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Conservation Status: Widespread Habitat, But Localized Presence
Although not currently classified as endangered, Hylophilus moxensis faces potential threats. Bolivia’s Llanos de Moxos, the bird’s known habitat, is ecologically rich but increasingly pressured by human activity.
“The recognition of Hylophilus moxensis as an additional endemic taxon in the region should boost conservation prioritization efforts,” the researchers wrote. “Rampant burning for large-scale agriculture is an acute problem in the region for biodiversity.”
Still, the team remains cautiously optimistic. “Although we are unable to estimate a population size for Hylophilus moxensis, we do not believe it to be currently threatened, because suitable habitat is still widespread in the region.”
What remains unclear is the bird’s actual population size and distribution. The relatively few recorded sightings may suggest more than just poor sampling. “The relatively few records of the species may point towards other factors than a lack of observers and may reflect a truly localized occurrence,” the paper adds ,raising the possibility that this bird is rarer than currently assumed.
NOTE – This article was originally published in Indian Defence Review and can be viewed here
