Rattus norvegicus

Rattus norvegicus

Rn was detected in natural habitats on three of the main islands and on Tsushima Island (Table 1, Figure 1).

On Hokkaido, we found two trackways in March and observed one animal (Figure 5) in August in Kushiro Marsh, the largest remaining natural wetland in Japan. All three records were along the edges of wood patches surrounded by reedbeds, tall grass and patches of open water (Figure 6). One trackway was found in March in Kiritappu Marsh (a similar but smaller wetland) in a large reedbed ~ 50 m from the edge of mixed forest. We also found one trackway in December on a snow-covered beach in Shiretoko National Park, but it was less than 1 km from residential buildings. That trackway appeared to be a well-used path ~ 30 m long, connecting a burrow in the coastal cliff with intertidal zone, where more than a hundred fragments of broken shells of periwinkles (Littorinidae) were scattered among the rocks. The intertidal zone in this area also had numerous limpets, crabs, sea stars, sea urchins, kelp plants, and other possible food items. In Daisetsuzan National Park we found one trackway in March in riparian forest of birch (Betula sp.) (Figure 7), and observed one animal in August as it was feeding on Geometridae moths on a paved road through oldgrowth mixed montane forest (Figure 8), near a small stream lined with alder (Alnus sp.). The moths were flying in great numbers that night, and covered the road pavement at densities of up to 3 moths per 1 m 2 of the road (visual estimate). Numerous other mammals, birds and amphibians were also feeding on them.

On Honshu and Kyushu Rn was recorded only in wetlands. On Honshu, at least six individuals were seen in June walking and feeding (on unidentified small seeds) along the edges of reedbeds of Tone River near Sasagawa, one was observed in August running across an opening in a small wetland on Niigata Plain, and 12 were seen in December running and swimming in flooded woodlands along the shores of Lake Biwa. However, all those locations were within 1 km of residential buildings and/or ricefields.

On Kyushu, one Rn was seen in December running across a sedge meadow in Bogatsuru Marsh, a unique high-elevation wetland inside a volcanic crater in Aso-Kuji National Park.

On Tsushima, two Rn were observed in August feeding on crabs in the intertidal zone in Aso Bay Park, along a shoreline lined with deciduous forest and wetlands (Figure 9). One was seen entering a burrow in a steep clay slope ~ 3 m from the water edge at high tide; the burrow had likely been built by the rat, as similar waterside burrows are commonly built in riverbanks by human-independent Rn in Russian Far East (Kuzyakin 1951). Local people reported rats to be common along the island’s coast.