New songbird species discovered in Japan

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", says Urban Olsson, professor emeritus at the Department of Biological & Environmental Sciences, and one of the people in the Swedish research team. 

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.

"The discovery highlights the vital role of genomic research in revealing hidden biodiversity and provides an essential foundation for future conservation efforts", Urban Olsson concludes.