Mustela itatsi was historically native to three of Japan’s four larger islands: Honshu, Kyushu, and Shikoku. Over the past century, they have been introduced to most other Japanese islands for the purpose of rodent control. The current range includes Hokkaido and the majority of the Ryukyu Islands.
Biogeographic Regions: palearctic (Native )
Other Geographic Terms: island endemic
As with all weasels, Mustela itatsi has a long, slender body with short legs and a stout neck and head. Japanese weasels are larger weasels; adult males have a body and tail length between 45 and 52 cm and an average weight of 400 g. Females are generally smaller. Their coats are usually golden-orange with lighter coloring on the belly, and darker markings near the face. In response to the shortening of daylight, weasels stop producing melanin and their coat turns white and becomes thicker in preparation for winter.
Although their body is well-suited for running down tunnels and into tight spaces, it is not very efficient for retaining heat and energy. Weasels must continually search for food to overcome this disadvantage.
Range mass: 150 to 450 g.
Range length: 40 to 52 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Japanese weasels are found in a wide variety of Japanese ecosystems, but primarily mountainous and forested areas near moving water. Most hunting is done along rivers, but these weasels occasionally venture into grasslands or suburban areas.
In winter, these slim-bodied weasels spend most of their time beneath the snow chasing small rodents through a maze of tunnels. After catching and eating prey, Japanese weasels often enjoy the warmth of the quarry’s nest after eating.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: savanna or grassland ; forest ; mountains
Aquatic Biomes: rivers and streams
Other Habitat Features: suburban ; agricultural ; riparian
Habitat and Ecology
Since they are able to live in a wide range of Japanese habitats, these weasels have a wide range of prey options. They prefer to catch live prey such as rodents, amphibians, reptiles, birds, and some crustaceans. These weasels are also nest raiders, and enjoy bird eggs or young chicks. A common prey bird species is the Japanese bush warbler (Cettia diphone). When prey is scarce they resort to eating various fruits and berries. When food is abundant it is common for weasels to cache food items for later consumption.
Animal Foods: birds; mammals; amphibians; reptiles; fish; eggs; insects; terrestrial worms; aquatic crustaceans
Plant Foods: fruit
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Eats terrestrial vertebrates)
Japanese weasels help in controlling rodent and other small animal populations. There is also evidence that they are effective at spreading seeds through feces.
Ecosystem Impact: disperses seeds
- Paragonimus ohirai
- Gnathostoma nipponicum
Despite their carnivorous lifestyle, the small body size of Japanese weasels make them a target to some large predators, mainly birds of prey. Their musky scent makes them less palatable to mammalian predators.
- diurnal raptors (Falconiformes)
- nocturnal raptors (Strigiformes)
Life History and Behavior
In order to communicate with other weasels or other animals, Japanese weasels use two main modes of communication: chemical and acoustic. Individuals secrete a substance known as musk from their characteristic anal glands, used in chemical communication. Weasels are territorial and establish territorial boundaries by rubbing their glands over obstacles such as branches and stones. Scent marks communicate gender, age, social status, health, and breeding condition.
Japanese weasels emit a wide range of calls and sounds. Primary calls include a low intensity trill, chirp, bark, screech, and hiss. Trilling generally signifies comfort when a mother is with her young. Chirping is another content call when danger is not present. Barking, screeching, and hissing all indicate imminent danger.
Communication Channels: acoustic ; chemical
Other Communication Modes: scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
Lifespan in Mustela itatsi is similar to other members of the genus Mustela. As a close comparison, M. sibirica has lived up to 8 years in captivity. Longevity in the wild is highly dependent on food availability. Average lifespan is likely to be 2 to 3 years.
Status: wild: 5 (high) years.
Status: wild: 2 years.
The mating process for M. itatsi starts off with the male seeking out females by smelling and analyzing their scent marks. Once he tracks down a female, a mix of play and biting occurs from a few hours to several days. When the female is ready, she allows the male to bite her around the neck and pin her down. Copulation is brief, but may take place multiple times for each couple. Soon after, they go their own ways and likely never see each other again.
Mating System: polygynous
Mating occurs from early May to late June. However, if there is a particular abundance of food, mating may occur until August, producing a second litter during the season. After mating, gestation takes about 30 days. The number of kits varies from 2 to 12, but is usually 5 or 6. It takes 8 weeks to fully be weaned and independent. Japanese weasels are sexually mature at one year old.
Breeding interval: Japanese weasels generally breed once yearly, although second litters may occur in years with abundant food resources.
Breeding season: Mating occurs from early May to late June or into August.
Range number of offspring: 2 to 12.
Average number of offspring: 5.
Range gestation period: 26 to 29 days.
Range weaning age: 8 to 9 weeks.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Females are solely responsible for parenting in Mustela itatsi, from conception to independence. Males leave females once mating is complete. Mothers will build nests in abandoned holes, cavities, or logs using grasses, feathers, and animal fur. Once the kits are born, their mother feeds them milk until their canines develop fully and they can consume flesh. Once old enough to move about, young weasels practice valuable hunting skills through play behavior. Soon after, they tag along with their mother to go hunting. Once they can hunt on their own, they’re considered independent and leave their mothers protection to find their own territory.
Parental Investment: altricial ; female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
Although their populations are in slight decline, Japanese weasels are listed on the IUCN Red List as Least Concern because of their widespread population across Japan. The primary threat to Japanese weasels is habitat loss due to residential and commercial development.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2003Not Evaluated(IUCN 2003)
- 2003Not Evaluated
Relevance to Humans and Ecosystems
Japanese weasels also occasionally prey on domestic birds, such as chickens and ducks.
In the past century Japanese weasels have been introduced to many of Japan's small islands to kill rats that were damaging crops. Along with the use of some rodenticide, the weasels helped reduce rat populations.
Japanese weasels are also trapped and used in the fur industry.
Positive Impacts: body parts are source of valuable material; controls pest population
The Japanese weasel (Mustela itatsi) is a carnivorous mammal belonging to the genus Mustela in the family Mustelidae. It is native to Japan where it occurs on the islands of Honshū, Kyūshū and Shikoku. It has been introduced to Hokkaidō and the Ryukyu Islands to control rodents and has also been introduced to Sakhalin island in Russia.
It is often classified as a subspecies of the Siberian weasel (M. sibirica). The two species are very similar in appearance but differ in the ratio of tail length to head and body length. There are also genetic differences which suggest that the two diverged around 1.6-1.7 million years ago. Their ranges now overlap in western Japan where the Siberian weasel has been introduced.
Adult males of the Japanese weasel can reach 35 cm (14 in) in body length with a tail length of up to 17 cm (6.7 in). Females are smaller. The fur is orange-brown with darker markings on the head. The species typically occurs in mountainous or forested areas near water. Its diet includes mice, frogs, reptiles, insects and crayfish.
- Abramov, A. & Wozencraft, C. (2008). Mustela itatsi. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 21 March 2009. Database entry includes a brief justification of why this species is of least concern
- Masuda, Ryuichi & Michihiro C. Yoshida (1994) "Nucleotide sequence variation in Cytochrome b genes in three species of weasels Mustela itatsi, Mustela sibirica and Mustela nivalis, detected by improved PCR product-direct sequencing technique", Journal of the Mammalogical Society of Japan, 19 (1): 33-43.
- Kodansha (1993) Japan: an illustrated encyclopedia, Kodansha, Tokyo.
- Wilson, Don E. & DeeAnn M. Reeder (eds.) (2005) Mustela itatsi, Mammal Species of the World, 3rd edition, Johns Hopkins University Press.
- Sekiguchi Keishi, Ogura Go, Sasaki Takeshi, Nagayama Yasuhiko, Tsuha Kojun, Kawashima Yoshitsugu (2002) "Food habits of introduced Japanese weasels (Mustela itatsi) and impacts on native species on Zamami Island", Mammalian Science, 85:153-160. [Abstract]