The feral American mink’s predation on small rodents and competition with other predators have been a concern. In some foreign countries, small native rodents have decreased in population under predation pressures from alien American minks, and the vegetation around the mink’s habitats has changed drastically. Influence of the American mink on small native rodents was studied by examining the habitat conditions and seasonal change of prey, and the distribution patterns of small rodents sharing the habitat with the American mink. American minks were caught on camera traps night and day, most frequently around noon. Signs of the American mink were observed around the confluence of Kushiro River. In their dung, small rodents’ hair and bones were detected. A number of small rodents were captured where the understorey is abundant, especially on sasa-type forest floors. We assumed that the American mink can adapt themselves to the environment in which they are highly populated and thus apply high predation pressures on small rodents.

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The mammal fauna and birds on and around the Tsuru University campus in central Japan was investigated using camera traps. The purpose was to understand the habitats of mammals and to compare the results to the authors’ previous investigation in the same area from 2009 to 2011. A total of seven automatic cameras were set up at two points on the Tsuru campus and at five points at Mt. Ozaki from November 2011 to April 2016. A total of 5,789 days were spent for photography. Pictures of 17 species of mammals and 19 species of birds, aside from bats and crows, were obtained. Five new species, Japanese Dormouse, Japanese Serow, Asiatic Black Bear, Raccoon, and Japanese Macaque, were recorded. The results of this investigation suggest that the sika deer population has increased and that the domestic cat distribution at Mt. Ozaki has expanded.

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A device for outdoor recording of images of hunting behavior of the Japanese water shrew, Chiarrogale platycephala, was developed and the effectiveness of the device was examined. A simple water tank that anyone could use was employed to produce the device. The glass tank was 150mm(W)×600mm(L)×350mm(H). A plastic net was placed at the outflow point to prevent bait fish from escaping. Good care was taken to minimize the effect on the river ecosystem. Another plastic net was employed to ensure that the water shrew could enter the device safely. The device may also be used as a teaching material and for exhibition at zoos.

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The Japanese medaka is designated as an endangered species because of its decreasing population, and conservation of the medaka is an urgent concern. In the present study, in order to obtain basic information for conservation of wild medaka, we observed the reproductive behavior of female medaka (Oryzias latipes, orange-red variety and wild fish) in experimental aquaria under various environmental conditions. Female medaka normally deposited eggs on aquatic plants or aquatic mosses which were solid with a soft surface in experimental aquaria. However, the fish did not deposit eggs but discarded eggs in aquaria provided with sand, floating aquatic plants, and no substrate, and in an aquarium lined with concrete. These results indicate that a suitable substrate is essential for successful egg deposition of medaka, and suggest that maintaining suitable vegetation in natural environments is important for conservation of wild medaka.

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The Fukushima Daiichi Nuclear Power Plant accident released large amounts of radioactive substances into the environment and contaminated the soil of Tohoku and Kanto districts in Japan. Removal of radioactive materials from the environment is an urgent problem, and soil purification using plants is under consideration. This study monitored accumulation of radioactive cesium in wild plants grown on a grassy plain in Iwaki City, Fukushima Prefecture, to choose a plant species to use for the decontamination. Many plant species did not accumulate high levels of radioactive materials expect for Lamium purpureum, Pueraria lobata, Taraxacum officinale, T. platycarpum, and Vicia sativa subsp. nigra. These species accumulated 501 to 1,450 Bq/kg dry weight of ¹³⁷Cs in the shoots.

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