Nina Foster / 31 Oct 2025
As taxonomy evolves, so does the Search for Lost Birds. Each update to the lost birds list accounts for not only rediscoveries, extinctions, and new species that fit the definition of “lost,” but also taxonomic clarifications. Using molecular techniques, researchers can now determine evolutionary relationships with more confidence than ever before. Some species maintain their original designations, while others are lumped together or split apart. Resolving these taxonomic uncertainties helps to prioritize conservation efforts and better protect biodiversity — and there are plenty of questions that remain unanswered.
Ornithologists once classified birds based on morphological traits and vocalizations. But in the late twentieth century, it became easier and more affordable to obtain and analyze genetic material. Researchers could extract and sequence DNA from museum specimens and, if available, extant individuals. These molecular methods have helped settle long-standing taxonomic disputes, sometimes supporting the validity of a species, splitting one species into multiple, or identifying aberrant individuals, subspecies, or hybrids.
Taxonomic clarifications guide the distribution of conservation resources, most of which are directed toward species. “It is much easier to attract attention to the plight of a threatened species than it would be if that same population were an unrecognized subgroup,” explains David Wiedenfeld, American Bird Conservancy’s Senior Conservation Specialist. “Plus, it’s much easier to raise funds and bring legal or regulatory resources to bear for a species’ conservation.”
These findings also allow authorities to more accurately assess extinction risk. Population size and geographic range are important parameters in determining whether a species is threatened. If one species is split into several, those representing a small fraction of the original population may become a higher priority for conservation action.
Some species on the lost birds list have undergone molecular analysis to determine their taxonomic designation. The Negros Fruit-Dove, for instance, is known from a single specimen collected in the Philippines in 1953. Last year, researchers confirmed the bird’s status as a distinct species by analyzing the type specimen’s DNA.
The results can also go in the other direction. In 2018, researchers published a DNA analysis of the White-chested Tinkerbird, a species whose legitimacy has been debated since its discovery in Zambia in 1964. The study authors, who called for further genetic analysis to support their findings, concluded that the White-chested Tinkerbird is not a distinct species. Instead, it is likely an aberrant individual or a subspecies of the Yellow-rumped Tinkerbird.
Most recently, a preprint publication described a molecular and morphological analysis of the Nechisar Nightjar, an enigmatic species evidenced by nothing more than a single wing collected in Ethiopia in 1990. The authors suggested that the lost nightjar is not a distinct species, but a hybrid. If the study passes peer review and the relevant taxonomic authorities remove the Nechisar Nightjar as a species, the bird will have been “found” — not by photographs, sound recordings, or physical documentation, but by the resolution of its taxonomic designation. Researchers are currently tackling similar projects to evaluate the validity of other lost bird species, such as the Rio de Janeiro Antwren and the recently rediscovered White-tailed Tityra.
Nine taxonomic mysteries on the lost birds list are still waiting to be solved with molecular methods. The following species are scarcely represented in bird collections, with little to no further evidence of their existence. Their taxonomic identities have been called into question, and many are categorized as Data Deficient on the IUCN Red List (marked with *), meaning there is not enough information to assess their risk of extinction. Hopefully, these birds will be rediscovered in the wild, prompting further research and conservation actions. But, like the Nechisar Nightjar, they might also be found in the lab.
Blue-wattled Bulbul*
Known from only two specimens — one from Sumatra in 1900, and another from Borneo in 1937 — this olive-yellow bird is among the most poorly known species in Asia. While reflecting on his 1992 sightings of the bulbul in Brunei, ecologist Robert Williams suggested that the Blue-wattled Bulbul may be a morph of another species, a genuinely rare habitat specialist, or a hybrid. He favored the last theory, pointing to the Black-headed Bulbul and Gray-bellied Bulbul as likely parents. However, these hypotheses have yet to be tested.
Cayenne Nightjar*
This species was described from a single male specimen collected in northwestern French Guiana in 1917. So far, all efforts to relocate the lost nightjar have been unsuccessful, although possible sightings were reported in French Guiana in 1982 and 1999. Morphological comparisons of the type specimen with the commoner Blackish Nightjar and the widespread Common Pauraque appeared to support the validity of the Cayenne Nightjar as a distinct species, but molecular techniques would resolve any lingering uncertainties about its taxonomic status.
Guanacaste Hummingbird
Lost to science for 130 years, this Critically Endangered hummingbird is known from only one specimen collected on the Volcán de Miravalles in northwest Costa Rica in 1895. The hummingbird was widely regarded as a subspecies of Indigo-capped Hummingbird until a detailed analysis of the lone specimen in 2016 suggested that it should be recognized as a distinct species. The study authors noted that genetic analysis would yield more information concerning the taxonomic relationships of this unique hummingbird.
Mayr's Swiftlet*
Only three specimens of this large, grayish-brown swiftlet have ever been collected — one from the Solomon Islands in 1927, and two from Papua New Guinea in 1963 and 1979. Field records of the species remain unconfirmed due to identification challenges. Formerly considered conspecific with Whitehead’s Swiftlet, Mayr’s Swiftlet is generally accepted as a distinct species. However, its taxonomic designation remains uncertain and it shares morphological traits with Uniform Swiftlet, leading to the possibility that is a form of that species.
Red Sea Swallow*
Controversy has surrounded this species’ identity since its discovery. The stocky, martin-like swallow is known from just one type specimen, which was found dead on an islet in Sudan in May 1984. Some experts have hypothesized that the Red Sea Swallow is an aberrant South African Cliff Swallow, although the specimen was collected hundreds of kilometers from the South African Cliff Swallow’s known breeding areas. Others have proposed that it might be a hybrid. Analyzing the DNA of the wings or tail that remain of the type specimen would shed light on the swallow’s mysterious origins.
Turquoise-throated Puffleg
This species is known from seven specimens — six collected during the nineteenth century, and one in 1963. Only two of the specimens have locality information, taken from north and central Ecuador. Habitat loss at the type locality and unsuccessful searches for the hummingbird have led to its classification as Critically Endangered (Possibly Extinct). The Turquoise-throated Puffleg is generally considered a distinct species, but researchers have suggested that the lost bird could be a hybrid, and its taxonomic designation has yet to be confirmed with molecular methods.
Yellow-legged Weaver
There are fewer than 10 known specimens of the Vulnerable Yellow-legged Weaver, taken from the Ituri Forest in the Democratic Republic of the Congo between 1910 and 1959, and only two subsequent sightings of the species in 1990 and 1994. The bird’s morphological similarities with the Vieillot’s Black Weaver and Maxwell’s Black Weaver have led some to suspect that the lost weaver is a hybrid of the two species. However, proponents of the hybrid theory have struggled to explain the weaver’s distinct yellow legs and greenish sheen, or why the proposed parents would hybridize in such a specific area at the easternmost fringe of their ranges.
Coppery Thorntail*
This hummingbird species is known from two nineteenth-century specimens whose precise location of origin is unknown, accompanied by the label “Bolivia?” The species has been neither reported nor collected since its initial description in 1852, prompting some to question its taxonomic validity. The specimens could have been hybrids, or represented immature or variant plumages of the Racket-tailed Coquette. A 1999 analysis of their plumage color and morphometrics supported the Coppery Thorntail’s classification as a distinct species, but the specimens have not undergone genetic analysis.
Tana River Cisticola*
This species was first described in 1967 based on six specimens collected in the lower Tana River region in Kenya. The specimens were originally identified as Ashy Cisticolas, but ornithologist Melvin Traylor noticed peculiar morphological traits that led him to describe the bird as a distinct species. However, there are several points in Traylor’s analysis where he expresses doubt with his own classification. The type specimens may represent aberrant individuals or hybrids of other cisticola species. DNA analysis of the museum specimens would help taxonomists reach a final conclusion.
Nina Foster is a science communication specialist with interests in ornithology, forest ecology, and sustainable agriculture. She holds a BA in English literature with a minor in integrative biology from Harvard University and is currently an environmental educator at Schoodic Institute at Acadia National Park.