Aerial surveys were conducted to estimate the abundance of wintering populations of Steller sea lions (SSLs; Eumetopias jubatus) in the Sea of Japan originated from Russian waters using the line transect sampling method during spring from 2005 to 2019. The survey areas covered the continental shelf off the western coast of Hokkaido. A total of 28 196 km survey effort was made through the study period under suitable sighting conditions. The numbers of SSLs in haul-out sites were counted separately. Estimations and model selection for the effective strip width were carried out using the maximum-likelihood method. The abundance estimates of SSLs with the line transect method varied annually, ranging from 284 animals (coefficient of variation [CV] = 0.732) in 2016 to 6271 (CV = 0.194) in 2014. This large variation in abundance estimates might be attributable to interannual changes in the survey coverage, spatial distribution, haul-out behaviors, and seasonal variation of wintering populations of SSLs in the waters off Hokkaido. This warrants further investigation of seasonal and annual change of distribution to adjust key information on the abundance estimates reported here for use in the conservation and management of this species.

Striped dolphins (Stenella coeruleoalba) mass-stranded on 26 April 2013 at Minamisatsuma, Kagoshima Prefecture, in southern Japan (East China Sea). The diet of the mass-stranded striped dolphins was investigated to reveal their foraging pattern through analyses of the stomach contents and stable isotopes in muscle. Of 26 stomachs sampled, 25 contained hard parts of prey animals; no fleshy remains were found in any of the stomachs. The identified prey species represented four cephalopod families: Loliginidae, Onychoteuthidae, Histioteuthidae, and Ommastrephidae. Among these, ommastrephids had the highest abundance (42.4%) and frequency of occurrence (69.2%). A chi-square test revealed that the prey species consumed did not significantly differ between male and female dolphins, although deeper-water squids (Onychoteuthidae and Histioteuthidae) appeared only in the stomachs of females. The values of δ¹³C ranged from –20.4 to –17.0‰ (mean ± SD: –18.2 ± 0.9‰), and values of δ¹⁵N ranged from 10.2 to 12.5‰ (10.8 ± 0.5‰), with a significant difference in δ¹⁵N between sexes (P < 0.05).

Despite of great variation of food habits of the raccoon dogs (Nyctereutes procyonoides) on the Japanese archipelago, information of the food habits of them in the warm temperate zone in southern Japan is limited. The food habits of them on Suwazaki Peninsula in western Shikoku Island, southwestern Japan, were studied using fecal analysis. The sampling period spanned May 2019 to April 2020. The point-frame method was adopted. Fruits (pericarp and pulp) were important, accounting for > 30% in autumn and > 20% in winter. The fruit of Aphananthe aspera was particularly important, but various fruits were eaten in seasonal succession, and many fleshy tree fruits in the warm temperate zone were utilized. Insects were also important, accounting for > 20% in spring, summer, and early winter. Mandarin oranges comprised about 40% of the diet in late winter. Mammals and birds were less utilized than in other areas. The food habits of raccoon dogs on Suwazaki Peninsula were characterized by the diverse fruits and insects of the warm temperate zone together with cultivated mandarin oranges. These results suggest the opportunistic food habits of the raccoon dog.

Fauna of the Kuril Islands is understood insufficiently; in particular, the distribution and taxonomic relationships of bats in this territory are definitely understudied. Long-eared bats (Plecotus spp.) were first captured on the island of Urup during an expedition organized by the Russian Geographical Society in 2019. This capture became the first record of an indigenous land mammal on this island. Based on the peculiarities of geography, we assumed that the Japanese species P. sacrimontis would live on the Urup and Iturup Islands, as well as on the neighbouring Kunashir. However, a morphometric analysis of skull measurements and an analysis of the mitochondrial cytb gene show that long-eared bats from these two islands belong to the mainland species P. ognevi. This unexpected result raises questions regarding the postglacial history of the invasion of the long-eared bats to the islands, which probably occurred in two stages, and the taxonomic relationship between P. sacrimontis and P. ognevi.

It's not always possible to obtain samples from dead male pinnipeds that are fresh enough to determine the histological characteristics of spermatogenesis and their stage of sexual maturity. We propose that the morphometrics of genital organs of northern fur seals, Callorhinus ursinus, can be used as a new indicator of sexual maturity. We analyzed data from collected records of male fur seals around Hokkaido during 2011–2017 to examine morphometrics of genital organs and their stage in histological characteristics of spermatogenesis. First, we investigated ontogenetic and seasonal variation in three genital organs: testes, epididymides, and bacula. Second, we classified the stages of histological characteristics of spermatogenesis into three groups (Stage A–C) using non-linear discriminant analysis, based on the stage in histological characteristics of spermatogenesis determined by histological observation of seminiferous tubules. Testicular size, testicular mass, and epididymal mass showed seasonal variation associated with spermatogenesis. From our analysis, the stage in histological characteristics of spermatogenesis could be estimated using testicular mass with high accuracy of predicting spermatogenesis. And measurement of baculum was suggested to be an indicator of predicting sexual maturity. We conclude that this simple estimation may be used to determine sexual maturity based on individual growth patterns.

We determined species diversity, seasonal reproduction, and echolocation patterns in the bat community of Bidoup Nui Ba National Park (BNBNP), Lam Dong Province, on the Dalat Plateau of the Central Highlands of Vietnam. We documented 27 species with 211 individuals captured in 26 994 m² mist-net-hours and 3015 m² harp-trap-hours of effort. We found five species of pteropodids and 22 species of insectivorous bats in four families, including regional records and species seldom captured in Vietnam. Bat species richness at BNBNP is now known to be 33 species, including six found in a prior study. Based on the inverse Simpson Index of Diversity, evenness of captures was low, reflecting the high abundance of a few species with many species documented by just one or two individuals. Insectivorous bats were pregnant in the late dry season, but not during the wet season when lactation occurred and volant juveniles were captured. Echolocation call characteristics were determined for 19 species of insectivorous bats. Call patterns were consistent with some but not all reports in the literature from elsewhere in southeast Asia. This suggests the existence of cryptic species or geographic and habitat variability in echolocation calls of southeast Asian bats that requires further study.

In a heavy snowfall area in northeastern Japan, we clarified the diel activity patterns of and seasonal differences in three sympatric carnivores (red foxes, raccoon dogs, and Japanese martens) during winter and spring, and the interspecific differences among the activity patterns in each season. The activity time of the target species was obtained by camera-trap surveys at seven sites around the Experimental Forest of Yamagata University from January to June 2019. The diel activity patterns of each species, and seasonal and interspecific differences in the activity patterns were evaluated using the kernel density method. Red foxes showed a unimodal nocturnal pattern in spring, whereas they were also observed during the daytime in winter. Raccoon dogs showed a unimodal nocturnal pattern, and peak activity after sunset in both seasons. Japanese martens were clearly nocturnal during both seasons. Because there were a few interspecific differences in diel activity patterns among three species, species interactions had little effect on diel activity patterns. Our findings indicate that the diel activity of medium-sized carnivores responding to winter conditions may vary depending on species.

Age-specific changes in deer demographic parameters under food limitation are an important factor in predicting the post-population-crash dynamics of irruptive deer populations. To evaluate the differences in age-class-at-death between the initial irruption and post-population-crash phases of a sika deer (Cervus nippon) population, we analyzed a dataset of naturally dead carcasses from an introduced sika deer population on Nakanoshima Island, Japan. We predicted that the occurrence probability of fawn-class sika deer carcasses would increase in the post-population-crash phase and that the occurrence probability of old-class sika deer carcasses (≥ 10 years old) would decrease during this phase. Contrary to our expectations, the relative occurrence probabilities of four age classes [fawn, yearling, prime-aged (2–9 years old), and old] of sika deer carcasses did not differ between the initial irruption and post-population-crash phases. This could partially be a side-effect of classifying deer age into just four categories; slight changes within the age classes could not be detected because of this statistical limitation. Comparative studies are required to determine whether these results coincide with other irruptive deer populations.

Individual identification is an important technique in animal research that requires researcher training and specialized skillsets. Face recognition systems using artificial intelligence (AI) deep learning have been put into practical use to identify in humans and animals, but a large number of annotated learning images are required for system construction. In wildlife research cases, it is difficult to prepare a large amount of learning images, which may be why systems using AI have not been widely used in field research. To show the potential for the development of a system that identifies individuals using a small number of learning images, we constructed a system to identify individual Japanese macaques (Macaca fuscata yakui) from a small number of candidate individuals from an average of 20 images per individual. The characteristics of this system were augmentation of data, simultaneous determination by four individual identification models and identification from a majority of five frames to ensure reliability. This technology has a high degree of utility for various stakeholders and it is expected that it will advance the development of individual identification systems by AI that can be widely used in field research.