Japanese dormouse (Glirulus japonicus)

GenusGlirulus (1)
SizeHead- body length: 65 – 80 cm (2)
Tail length: 40 – 55 cm (2)
Weight14 – 40 g (2)

Classified as Least Concern (LC) by the IUCN Red List (1).

Dormice are the intermediates, in form and behaviour, between mice and squirrels, and this attractive Japanese dormouse is the only species in the genus Glirulus (3). It has soft and thick, pale olive brown fur, with a dark brown or black stripe running along its back. In front of the ears is a tuft of longer hair, and the bushy tail is flattened from top to bottom (2). The four digits of the forefeet and the five digits of the hindfeet have short, curved claws, and the undersides of the feet have a cushion-like covering, all enabling the dormouse to grip to branches and move around trees with great agility (3).

Occurs on the Japanese islands of Honshu, Shikoku, and Kyushu (2)

The Japanese dormouse inhabits mountain forests, generally at elevations between 400 and 1,800 meters (2).

The Japanese dormouse is a nocturnal rodent that spends the night ranging over a relatively large area searching for food, with males covering greater distances than females (2) (4). It is an agile climber and spends the vast majority of its time in trees, feeding on seeds, fruits, insects and birds’ eggs (2). Dormice are the only rodents to lack a cecum, which indicates the lack of cellulose in their diet. The daytime is spent in round nests, constructed from bark and covered on the outside with lichens (2). Generally, these nests are situated in tree cavities, but they can also be found in shallow underground sites or in rock crevices (4).

A defining feature of dormice is their long hibernation period, which gave rise to their name; ‘dormeus’ is an Anglo-Norman word meaning sleepy one. They accumulate layers of fat prior to hibernation, which can last for up to seven months. As soon as they emerge from hibernation, dormice will begin to mate (3). They have a well developed ability to vocalize, which plays an important part in mating. Gestation lasts for about one month, after which an average of four naked and blind young are born in June or July (2) (3). After around 18 days the young open their eyes and are able to hear, and after four to six weeks, they become independent. Sexual maturity is reached after one year, and dormice live for between three and six years (3).

Whilst dormice are naturally found at far lower densities than other rodent groups (3), this natural scarcity has been exacerbated by the activities of humans. The primary cause of decline of the Japanese dormouse in the past, and the greatest continuing threat, is habitat loss. The montane forests of Honshu, Shikoku, and Kyushu Islands have declined greatly in the past. Remaining tracts of forest continue to be threatened by logging, road construction, and the development of tourist facilities (5).

The Japanese dormouse has been designated a Natural Monument, meaning that the Commissioner for Cultural Affairs must approve any changes to the habitat of this species or any actions that would affect the preservation of the species (6). The Japanese dormouse occurs within the Shirakami-Sanchi Natural World Heritage Site and Nature Conservation Area. Situated in the mountains of northern Honshu, it is a remote area unaffected by man (7). The Kiyosato Educational Experiment Project (KEEP) runs a museum dedicated to the Japanese dormouse, and runs programs and classes to educate the public about this endangered species, carries out research, and encourages the protection of critical dormouse habitat (8).

For further information on the Japanese dormouse see:

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  1. IUCN Red List (December, 2009)