Black woodpeckers use suburban larch plantations in Sapporo as winter feeding grounds

A research group comprised of Associate Professor Shin Matsui and Researcher Sotaro Sarudate from the Graduate School of Biology at Tokai University, along with Research Administrator Akira Unno from the Forestry Research Institute of Hokkaido Research Organization, announced that they have revealed the "black woodpecker," a large woodpecker species designated as a natural monument, selectively uses larch plantations in the suburban areas of Sapporo City as important foraging sites during the severe winter. This finding is expected to promote both the conservation of the black woodpecker and the preservation of forests rich in biodiversity. The results were published in the Japanese Journal of Ornithology on November 11.

The black woodpecker is Japan's largest woodpecker species, characterized by its entirely black body with a red crown, and is designated as a national natural monument. In Japan, it inhabits northern Honshu and Hokkaido. While the regional population in northern Honshu is facing the threat of extinction, in Hokkaido it is distributed throughout forests across the entire prefecture.

It is known that throughout the year, the black woodpecker feeds on insects, primarily ants, with the tree species used for nesting and foraging being varied by region. Unlike other woodpecker species in Japan, it has the distinctive characteristic of excavating large holes in the trunks of living trees during winter to feed on ants and other prey. By modifying the physical environment of its habitat, it plays a role as an ecosystem engineer that also affects other organisms.

From the 1950s to 1970s, Hokkaido's natural forests were extensively logged, primarily in low-elevation areas, as part of the postwar afforestation expansion. They were then converted to plantations of Sakhalin fir and larch. Many of these plantations have now reached 50 to 60 years of age and are ready for cutting.

Meanwhile, the tree species and suitable sites used by black woodpeckers for foraging in the suburban forests of Sapporo were not well understood.

In this study, the research group examined the habitat selection of black woodpeckers inhabiting Sapporo City based on the distribution of foraging trees showing evidence of excavation and feeding on living tree trunks during winter.

As a result, it was revealed that black woodpeckers tend to use more trees with larger diameter at chest height in areas with lower elevations and higher proportions of conifers. Furthermore, it was found that larch, introduced to Hokkaido from Honshu, and Japanese white birch, a native pioneer tree species, are preferred as winter foraging trees.

To visualize potential foraging sites around winter foraging trees, an analysis was conducted using MaxEnt (a statistical model) using environmental factors such as topography and vegetation type as indicators. This revealed that the probability of suitable winter foraging habitat is higher at low elevations, in areas with a high proportion of larch forests, and on gentle, moist terrain. In contrast, the probability of suitable habitat decreased on north-facing slopes.

It was further demonstrated that by utilizing the distribution of winter foraging marks left by black woodpeckers and the suitable foraging sites estimated from them, it is possible to identify areas with high biodiversity which are locally formed within forests. This enables them to efficiently zone suitable winter habitats for forest birds.

Matsui said, "Through fieldwork conducted along survey routes totaling 90.8 kilometers in diverse forest environments in southwestern Sapporo City, we unexpectedly found numerous traces of the nationally designated natural monument black woodpecker excavating holes in the trunks of large-diameter larch trees, one of Hokkaido's main plantation species, to forage during winter. I believe that in mature lowland plantations adjacent to urban areas, securing the black woodpecker's main winter foraging grounds while also utilizing timber resources will contribute to the conservation of biodiversity."