The eruption of Mount Ontake in September killed dozens of hikers, but also probably decimated the population of a rare bird — the rock ptarmigan, a much-loved symbol of Japan’s alpine region.
The bird, called the “raicho” (thunder bird) in Japanese, is considered quite tame and has striking plumage that changes with the seasons: mottled in summer and mostly white in winter. The bird is designated as a Special Natural Monument by the Cultural Affairs Agency, and the Environment Ministry’s Regional Red List declares it an endangered species.
Experts believe the thick layer of ash left by the Sept. 27 eruption of the 3,067-meter volcano straddling Gifu and Nagano prefectures may have killed the plants the bird lives on and reshaped its habitat.
In Japan, ptarmigan live on slopes above about 2,500 meters. A lack of suitable habitat in the area leads experts to predict that the birds may leave.
A tally in the 1980s estimated the national ptarmigan population at about 3,000; that has since dropped below 2,000.
Amid a fall in hunters and a rise in temperatures, more deer are roaming the slopes and competing for food.
Scientist Yoshihiro Takeshita, an associate professor of geology at Shinshu University in Nagano, has been studying the ash since November. He is a member of the eruption monitoring committee at Mount Ontake.
The ash starts to get noticeable near the 2,400-meter mark, Takeshita said, thickening to 10 cm at around 2,700 meters.
It covers the roots of alpine plants, including the bird’s usual shelter, Siberian dwarf pines, and their food source, crowberry and bilberry.
Ptarmigan are usually found between 2,400 and 2,700 meters on Mount Ontake, known for its Siberian dwarf pines. But crowberry and bilberry plants are only about 10 cm tall, so they may be buried.
There is also the concern that heat from the ash killed the plants and will prevent seeds in the soil from germinating.
“If there is already an accumulation of 10 cm, there is a high risk that we may lose the plants necessary to maintain ptarmigan,” said Hiroshi Nakamura, professor emeritus of ornithology at Shinshu University.
Recent research conducted by the Chubu Regional Forest Office found that there were 513 ptarmigan living on the mountain, mainly in five areas.
Twenty-one of the birds were in the Kurosawa region to the east, which received much of the ash, and around 65 were spread across two areas around Otaki and Mamahaha peaks, where craters have formed.
Ptarmigan can typically be found near the 2,300-meter mark during the winter, when the peak is covered by snow.
In spring, they climb back up to around 2,700 meters, but experts predict that next year they may move to regions with less ash if their usual habitat lacks food and shelter. However, as Mount Ontake is a single summit mountain, Nakamura believes its ptarmigan population has less genetic diversity than the birds in the Northern Alps and is less susceptible to changes in the environment.
This section, appearing Saturdays, features topics and issues from the Chubu region covered by the Chunichi Shimbun. The original article was published on Dec. 3.