Scientists have identified a new, previously unknown species of bird in Japan after genetic research revealed that what was believed to be a single population actually consists of two distinct ones. This is the first time in more than 40 years, since 1982, that a new avian species has been recorded in the country, highlighting the ability of modern genetic tools to uncover hidden biodiversity in isolated ecosystems.
The research, published on June 23, 2026, focused on the Ijima Warbler, a migratory bird that is difficult to spot, found exclusively in two Japanese archipelagos. Although new species are described annually, this case stands out for the birds’ near visual identity, with DNA providing crucial evidence that they are separate species.
“This demonstrates the importance of using genetic methods to uncover hidden biodiversity, especially in a time of global biodiversity crisis. These methods can provide more complete knowledge to guide future nature conservation efforts,” said Per Alström of Uppsala University, one of the researchers involved in the discovery of the Tokara Warbler.
In-depth analysis confirms previously unidentified species
The Ijima Warbler (Phylloscopus ijimae) inhabits the Izu Islands, located south of Tokyo, and also the Tokara Islands, which are located about a thousand kilometers southwest. Approximately a decade ago, the first signs that birds from these two sets of islands had genetic differences were detected by researchers.
After analyzing the DNA sequences, scientists expanded their studies with intensive fieldwork on the islands, examinations of museum specimens, and complementary genetic investigations. Whole genome analyzes confirmed that the Tokara Islands population diverges significantly from the birds residing on the Izu Islands.
The detailed comparison of the birds’ songs reinforced the genetic discoveries, corroborating the distinction between them. As a result of these findings, scientists from Uppsala University, the University of Gothenburg and two Japanese institutions made the description of the Tokara Warbler official (Phylloscopus tokaraensis) as a new species.
This revelation is particularly notable because Japan has not documented a new bird species since 1982, when the Okinawa rally (Gallirallus okinawae) was described for the first time. The discovery of the Tokara Warbler therefore marks a significant milestone for Japanese ornithology.
“The new species is somewhat enigmatic and difficult to characterize. In visual terms, it presents no distinctions in relation to the Ijima Warbler. It is the DNA analyzes and song variations that reveal its nature as a distinct species”, explained Alström.
Small populations generate alert for bird conservation
Both species live in small island habitats, which naturally imposes a limit on the size of their populations. The Tokara Islands, for example, cover a total area of just over 100 square kilometers, spread over twelve islands, therefore being a smaller region than the island of Fårö, in Sweden.
The researchers found that the two species exhibit very low genetic diversity, which can increase their vulnerability to environmental changes, pressure on the habitat and the occurrence of diseases. However, there are also indications that populations may have shown some recovery after previously recorded declines.
Expanded protection for two rare bird species
The Ijima Warbler already appears as “Vulnerable” on the list of the International Union for Conservation of Nature and enjoys protection in Japan, being considered a “Natural Monument”. With the identification of the Tokara Warbler, which appears to be as rare as the Ijima Warbler, scientists recommend that both species receive the status of “Vulnerable”.
They also emphasize the importance of continuous monitoring to detect future changes in population size and ensure the long-term survival of these rare island bird species, contributing to the maintenance of regional biodiversity.
