Mammal Study

Although much research has accumulated on Sciuridae vocalizations, most of it has been on terrestrial squirrels, and there is still a significant knowledge gap regarding arboreal squirrels. Vocalizations of the Japanese squirrel, Sciurus lis, were investigated in the urban park of Iwate Prefecture, Japan. The Japanese squirrels produced “kuk” and “moan” in alert and “squeal” and “buzz” in social interactions. Of the “kuk” sounds, 58.2% were uttered toward cats, dogs, or observers, while 36.4% of the “moan” sounds were toward crows or hawks. In a playback experiment of two types of alarm calls, when the squirrels were on the ground, they immediately fled up the tree in response to the “kuk” sound but remained still in response to the “moan” sound. However, squirrels in the trees often responded to remain still for both sounds. These results indicated that “kuk” tends to be emitted against terrestrial mammals and “moan” against aerial birds, and the decision to flee or stay is more critical on the ground, where they are more vulnerable to predation. The two types of alarm vocalizations in the Japanese squirrel may function to ensure the rapid and appropriate escape behavior of nearby close relatives.

Published online 10 October, 2023; Print publication 31 January, 2024

Active acoustic emission from a mother to a calf after parturition is one strategy used to enhance recognition of mothers by calves and develop, then maintain, a mother–calf bond from an early stage. This study predicted that a high-calling postpartum period exists in a social delphinid, the Pacific white-sided dolphin (Lagenorhynchus obliquidens). This species produces pulsed call sequences for vocal exchange with conspecifics, and these sequences appear to be an important signal between mothers and calves. Sounds were recorded from three pregnant females at the Niigata City Aquarium, Marinepia Nihonkai, Japan, before and after each birth in 2019, 2020, and 2021 to investigate the rate of their pulsed call sequences. Continuous data from prior to four days to five days following parturition, opportunistic data within the last pre-parturition month, and data from the postpartum period were obtained from the females. The pulsed call sequence gradually increased during the last gestational month. A high-rate sequence was repeated daily for four days pre-parturition and faded within several hours postpartum, and few sequences were produced from the day after parturition. Contrary to our prediction, the many pre-parturition sequences and fewer postpartum sequences suggest a low efficiency of postpartum imprinting in this species.

Published online 20 October, 2023; Print publication 31 January, 2024

Morphological variation in the house mouse Mus musculus was examined based on five external body measurements and 25 skull measurements of 166 specimens from Honshu, Kyushu, Kikaijima Island, Okinoerabujima Island, Okinawajima Island, Miyakojima Island (my1 and my2), and Yonagunijima Island (yn) in Japan, as well as 99 specimens of M. caroli from Okinawajima Island (ca). In skull measurements, yn and my2 specimens were overlapped and distinct from the other localities in principal component analysis (PCA). Specimens of yn and my2 had shorter mandible heights. Although yn and my2 specimens overlapped with ca specimens in PCA using mandibular measurements, yn specimens had an elongated angular process reaching the posterior tip of the coronoid process, different from ca specimens with a more robust and long coronoid process. In this study, distinct morphological features were found on Yonagunijima Island. Specimens of my1 and my2 from Miyakojima Island differed from each other; my2 specimens were more similar to Yonagunijima Island specimens. The mandibular morphometric similarity between M. musculus from Yonagunijima Island and M. caroli from Okinawajima Island is presumably related to adaptations in producing similar mechanical advantages and equivalent masticatory forces.

Published online 20 October, 2023; Print publication 31 January, 2024

The purposes of this study were to ascertain the food habits of the Eurasian otter Lutra lutra L., in two types of riparian habitats. The study was conducted along a forest stream (Ungok Stream in Gyeongsangbuk-do, central-eastern part of South Korea) and a larger river (Seomjin River in Jeollanam-do, south-western part of South Korea). A total of 4268 spraints (faeces of otters) were analyzed for investigation of otter prey items. In the forest stream, fish were the primary prey items throughout the year (relative frequency of occurrence, RFO 64.74%), and other prey items included amphibians (17.37%), insects (8.82%), birds (4.74%), crayfish (0.57%), and mammals (0.54%). However, the RFO of fish (82.58%) was strikingly higher and the composition of amphibians (1.79%) was lower in the larger river system. The obtained information on food habits from different types of rivers will be helpful for the management of the endangered Eurasian otters, especially in forested countries.

Published online 26 October, 2023; Print publication 31 January, 2024

We conducted dietary analysis on 140 raccoon dog fecal samples, collected between March 2019 and February 2020 in a satoyama area in Tokyo, to see if any effects from competition with invasive raccoons were evident. Raccoon dogs mainly consumed fruits, seeds, and cultivated plants (frequency of occurrence 90.7%), earthworms (60.7%), and insects (48.6%). Dominant food types included summer tangerines (Citrus natsudaidai), and berries (e.g., Vaccinium spp.), with earthworms (Oligochaeta spp.) providing their primary source of protein. These raccoon dogs consumed more fruits but less insects than reported by other studies from Japan. We then compared our results with a previous study (2004–2005) in the same area, prior to the arrival of invasive raccoons. We detected minimal effects of raccoon arrival on raccoon dog summer or autumn diet, thus allowing raccoon dogs to find sufficient food to accumulate body-fat for over-wintering; however, their restricted winter diet diversity, with fewer animal species consumed, suggests that they may experience some protein limitation prior to the cub rearing season. The co-existence of raccoon dogs alongside invasive raccoons currently appears viable in this satoyama area, apparently enabled by the ability of raccoon dogs to shift their diet to include more fruit.

Published online 4 December, 2023; Print publication 31 January, 2024

Echinococcus multilocularis is a zoonotic parasite for which canid species are the definitive hosts. Its distribution in Japan has been limited to Hokkaido. Recently, however, feral dogs in the Aichi Prefecture have been continuously infected with E. multilocularis. This suggests that E. multilocularis is becoming endemic to Honshu, but its life cycle in this region is unclear. The feeding habits of the definitive host can be the key to understanding these details. In this study, we investigated the diet of feral dogs, known as the definitive hosts, and red foxes, a possible definitive host, on the Chita Peninsula, Aichi Prefecture, and examined their relationship with the life cycle of E. multilocularis. Dietary analysis showed that feral dogs fed mainly on plant matter including fruits, concentrated feed, and birds without consuming rodents that can act as intermediate hosts. In contrast, red foxes consumed Microtus voles, which are suitable intermediate hosts for E. multilocularis. Therefore, the route of infection of feral dogs with E. multilocularis remains unknown, but there is concern that the disease may spread to red foxes via Microtus voles.

Published online 10 October, 2023; Print publication 31 January, 2024

We observed that a captive melon-headed whale, Peponocephala electra, maintained close proximity to the abdomen of another member of Delphinidae. Therefore, we aimed to investigate whether this behavior was a “sleep” behavior by observing indicators, such as eye states and responses to external stimuli. The whale had at least one eye closed for more than 60 s and demonstrated fewer responses to external stimulation. These results suggest that the type of behavior exhibited by the whale was sleeping behavior. To the best of our knowledge, no prior studies have reported this behavior in cetaceans. We propose to coin the term “tandem sleep” to describe this behavior.

Published online 28 November, 2023; Print publication 31 January, 2024