In this review, we analyze the zoo records of sciurids (Rodentia) in Japan and discuss the risk management of non-native squirrels. On the basis of the annual reports of the Japanese Association of Zoos and Aquariums (JAZA), we summarized the number of squirrels kept in each JAZA member zoo from 1951 to 2011. This study revealed that among JAZA member zoos, (i) both the number of zoos keeping squirrels and the number of squirrels kept in zoos peaked in the 2000s, (ii) there was a shift from non-native to native species, and (iii) the number of Callosciurus erythraeus (an invasive alien species) individuals kept in zoos decreased significantly. We then selected five JAZA member zoos where C. erythraeus is known to occur in the surrounding area and conducted a literature review. This study showed that (i) several zoos were involved in the release or escape of the alien squirrel species, (ii) even small numbers of released/escaped animals can establish a new feral population, and (iii) artificial food supplementation can increase both the establishment and survival rates. We also present two examples of non-JAZA member zoos that may have been involved in the establishment of new feral populations of C. erythraeus and highlight the issues related to captive squirrels in Japan that need to be addressed.

Bottlenose dolphins (Tursiops truncatus), which are a well-known small odontocete species, are widely distributed worldwide. However, in captivity, they frequently display problematic behaviors, including regurgitation and reingestion. Therefore, methods for reducing such behaviors need to be developed to improve the well-being of these dolphins. In this study, we introduced boat fenders after daytime feeding to two bottlenose dolphins at Kamogawa Sea World as an environmental enrichment device to reduce regurgitation behavior. We compared their behaviors on days with and without the boat fenders. The results showed that introducing the boat fenders reduced both the number of regurgitation actions and the time until the last regurgitation. However, further research is needed to verify whether these beneficial effects of boat fenders persist and whether the same effects occur in individuals housed in other facilities.

An activity sensor embedded in a GPS collar allows for the remote and continuous recording of animal behavior. Moreover, accurate thresholds for behavior classification can be established by aligning the sensor values with actual behaviors, thereby providing effective information for clarifying the actions of animals. This study focused on establishing a threshold for “active” and “inactive” behaviors of the Japanese serow (Capricornis crispus), the nocturnal behavior of which poses challenges for its direct observation. We fitted a wild individual with an activity sensor-embedded GPS collar, thereby combining direct observation with sensor data to determine a reliable threshold for classifying “active” and “inactive” behaviors. The accuracy of the established threshold exceeded 95% based on 1,300 min of direct observations in video footage. Although this threshold was based on the data of only one individual, its importance lies in that it was determined on the basis of the behaviors of a wild individual. In future studies, the data acquired from multiple wild individuals will contribute to the further elucidation of the diel activity patterns of serows.

We introduce a simple and effective assistive device for holding small mammals captured in a cage trap. This device was developed to reduce the unintentional escape of captured animals and ensure their safe handling as well as protect against injury by trapped animals when treating them in the field. This article describes the steps involved in constructing the device. Users should use it legally at their own risk.

Two spherical nests of the harvest mouse (Micromys minutus) that were connected at the top and bottom were observed in a fallow field in Taki (Mie Prefecture, Japan). Awn leaves were used as the nest material, and the lower end of the nest was approximately 30 cm above the ground. Both nests were constructed between December 8 and 25, 2023, and no infants were observed. The two nests were connected by awn green leaves, and the presence of green leaves inside them suggests that both nests were built almost simultaneously.

From April 2021 to November 2022, we studied seasonal changes in the population size of the Japanese field mouse (Apodemus speciosus) in Ishinomaki (Miyagi Prefecture, northern Japan), focusing on its relationship with ground seed abundance. During the study period, mice were captured 115 times (36 individuals), with the capture frequency being particularly high during the summer. Juveniles were captured in July, September, October, and November, suggesting that these mice have two breeding seasons in Ishinomaki, similar to that of populations elsewhere in Honshu. Seed abundance was high in the fall, suggesting that food conditions were favorable for the mice during this season. Although seed abundance had no significant correlations with the number of mice captured in a month, it did have a significant negative correlation with the number of mice captured in the following month to at least two months later. The time lag between food conditions and capture numbers could be due to the period until the newborn mice were dispersed to the study site and/or until their foraging behavior changed in response to the ground seed abundance.

Recent information remains scarce on small mammals (Soricidae, Talpidae, Cricetidae, and Muridae) in a mountainous area at the western end of the Tokyo Metropolis. In this study, we conducted surveys of small mammalian fauna in plantations on the midslope (~1,000 m) of Mt. Akazasuyama (the peak at 1,332 m) as well as in subalpine coniferous and deciduous forests near the top of Mt. Kumotoriyama (the peak at 2,017 m) in summer and in autumn 2019, respectively, to prepare the 2020 Red List of Tokyo Metropolis. In total, 24 individuals of six species of talpids, murids, and cricetids were captured, confirming the inhabitation of Apodemus speciosus and Apodemus argenteus on Mt. Akazasuyama and Dymecodon pilirostris, Urotrichus talpoides, Craseomys andersoni, Craseomys smithii, and A. argenteus on Mt. Kumotoriyama. Notably, D. pilirostris and C. andersoni ranked as Near-Threatened species were recorded. The current species composition is not significantly different from that previouslyreported. However, owing to increased feeding pressure caused by the sika deer (Cervus nippon), the forest floor of Mt. Akazasuyama and some sites of Mt. Kumotoriyama have undergone aridification, which may affect small mammals.

Most subterranean mammals, including moles, are important ecosystem engineers that form underground burrows and tunnel systems and provide habitats for other species. However, few studies have focused on mole tunnels and only fragmentary information thereof is available. Thus, we used a “camera trap” method to detect the species that use mole tunnels in order to understand the details of their utilization, with the aim of revealing the ecological relationships between moles and other species. A trail camera was installed in the soil on the side of a tunnel of the lesser Japanese mole (Mogera imaizumii). Japanese shrew moles (Urotrichus talpoides) were detected 15 times, almost every day (7 of 8 days) during the study period, with most cases occurring five times per day. The duration and frequency of tunnel use were also determined. Although moles were previously repeatedly captured in this tunnel, shrew moles were not. Therefore, the camera trap method may be useful for detecting animals that use mole tunnels.

Humpback whales (Megaptera novaeangliae) are known to migrate seasonally from feeding areas at high latitudes to breeding areas at lower latitudes. Individuals can be identified according to the shape of their edges and color patterns of their flukes. Although the waters of the Ogasawara Islands are known as winter breeding or migratory areas for this species in the North Pacific, sightings of these whales have been reported in the waters around Miyakejima Island in the Izu Islands since 2018. As a result of identification surveys conducted during the 2022–2023 breeding season, two humpback whales identified off Miyakejima Island were confirmed as appearing off the Chichijima Islands in the Ogasawara Islands, approximately 800 km to the south. This is the first time that the same individuals have been confirmed in both regions during the same breeding season. Thus, our results indicate that these individuals used the waters around Miyakejima Island and the Ogasawara Islands during the 2022–2023 breeding season.

Understanding the roosting patterns of bats is crucial for establishing evidence-based approaches for conserving them and their habitats, given that they spend most of their lifetime roosting. The northern Ryukyu flying fox Pteropus dasymallus dasymallus is endemic to the Tokara Islands and Kuchinoerabujima Island, and the Japanese Government has assigned it as a national monument and critically endangered species. However, despite the high conservation status of the flying fox, their natural habits, including roosting behavior, remain unclear, especially on the Tokara Islands. Therefore, an efficient conservation approach has yet to be established by the government. On July 17, 2023, we found a solitary roost of an adult male flying fox on Akusekijima Island, the Tokara Islands and observed the behavior of the individual in both the roost and the nearby foraging site. The roost was located in a small forest along a valley approximately 200 m from the village. The flying fox rested during the daytime and often performed self-grooming. It exhibited territorial defense behavior approximately 30 min after sunset. This report contributes significantly to the conservation of this species, given that the natural environment varies among the islands and the ecology and behavior of this critically endangered flying fox is poorly understood.

Between November and December 2017, we radiotracked two Japanese flying squirrels (Pteromys momonga) to locate their daily rest sites in Ina City in Nagano Prefecture. As a result, we found that P. momonga used dreys on the branch in addition to the previously reported use of tree cavities. The dreys were constructed from the bark and branches of the Japanese cedar (Cryptomeria japonica).

The use of artificial structures as day roosts by Myotis yanbarensis, Murina ryukyuana, Hypsugo pulveratus, Myotis macrodactylus, and Rhinolophus cornutus orii on Amami Oshima Island, Japan was investigated in August 2023 and 2024. The artificial structures used by these bats were all located adjacent to an evergreen broadleaf forest. The locations for day roosting differed for each species. M. yanbarensis used holes in both tunnel ceilings and building walls, M. ryukyuana and H. pulveratus used holes in tunnel ceilings, M. macrodactylus used tunnel ceiling recesses, and R. c. orii used the ceiling walls of both tunnels and box culverts. Notably, the tunnels surrounded by the evergreen broadleaf forest provided various roost environments. Artificial structures and their surrounding forests may contribute to the conservation of bats.