A rare migratory songbird long thought to be a single species has now been shown to consist of two: the already-known Ijima’s Leaf Warbler (Phylloscopus ijimae), endemic to the Izu Islands, and the newly identified Tokara Leaf Warbler (Phylloscopus tokaraensis), restricted to the Tokara Islands. The new species is "cryptic"—nearly identical in appearance to Ijima’s Leaf Warbler but clearly distinct based on DNA analyses, supported by differences in song. Both species are found to have low genetic diversity.
Conservation concerns for island species
Because these birds live only on small islands, their populations are tiny. The study shows that both species have low genetic diversity, which means they may be vulnerable to future changes or diseases. Yet the birds also show signs that they may have recovered somewhat from past population declines. Ijima’s Leaf Warbler is already officially listed as Vulnerable and protected as a Japanese "Natural Monument". Researchers recommend that the newly described Tokara Leaf Warbler receive the same protective status, alongside targeted monitoring.
"This discovery shows how much biodiversity can remain hidden, even in birds that seem well known", says Daria Shipilina from the Department of Botany and Biodiversity Research at the University of Vienna. "By using genomic data, we were able to uncover a previously unrecognized species and provide the knowledge needed to protect it." The discovery highlights the vital role of genomic research in revealing hidden biodiversity and provides an essential foundation for future conservation efforts.
Scientific publication
Takema Saitoh, Daria Shipilina, Canwei Xia, Lijun Zhang, Shin-Ichi Seki, Urban Olsson, Per Alström, Discovering and protecting cryptic biodiversity: A case study of a previously undescribed, vulnerable bird species in Japan, PNAS Nexus, Volume 5, Issue 3, March 2026, pgag037, doi.org/10.1093/pnasnexus/pgag037
Contact
Dr. Daria Shipilina
Department of Botany and Biodiversity Research
Faculty of Life Sciences, University of Vienna
Rennweg 14, 1030 Vienna
E-Mail
