Japanese squirrels (Sciurus lis) are endemic to Japan; they have been seen on the Japanese islands of Honshu, Shikoku and Kyushu. Several populations of Japanese squirrels have recently become extinct on Kyushu and western Honshu, mostly due to habitat loss. (Tamura, 2011)
Japanese squirrels are considered habitat specialists, preferring lowland, natural mixed-species forests and pinewoods in subalpine areas, this species may avoid grasslands and shrub fields. Increased human activity has caused the extinction of certain suburban populations. (Kataoka and Tamura, 2009; Tamura, 2004; Thorington, Jr., et al., 2012)
Regardless of their gender, Japanese squirrels tend to be 160 to 220 mm from their head to the base of their tail, with an average tail length of 130 to 170 mm. They typically weigh between 250 and 310 g. Japanese squirrels are mostly brown on their dorsal side and white on their ventral side. They may have hints of red on their dorsum and patches of orange on their lower sides, shoulders and hips. Their tail is the same color as their dorsum, but can sometimes include white or buff colors. In winter, their pelage becomes grayer on the dorsum and tail. This species also has large eyes and ears, with low-crowned, lophodont teeth. Japanese squirrels belong to family Sciuridae. General characteristics of this family include a dental formula of 1/1, 0/0, 1/1, 3/3 for a total of 20 to 22 teeth, fully haired, bushy tails and five digits on their hind feet and four digits on their front feet. (Allaby, 1999; Anderson and Jones, 1984; Thorington, Jr., et al., 2012)
Female Japanese squirrels are receptive to breeding for very short periods of time, during this time, they are often followed by several males. Their mating system has not been reported; most squirrel species engage in a polygynous mating system, although some species have a polygynandrous system. (Sherman and Wauters, 2001; Thorington, Jr., et al., 2012)
Japanese squirrels are polyestrous and breed from February to March and May to June. The heaviest and most dominant males usually secure the most mates. Their gestation period is usually 39 to 40 days, after which, 2 to 6 young are born. The fertility of female European red squirrels, the closest relative to Japanese squirrels, is based on weight, dominance rank, length and habitat. Body weight, followed by rank, are the most important influences on fertility, the heaviest, dominant females are the most fertile. European red squirrels wean their young in about 62 days, after which, females and males become sexually mature when they are about 296 and 320 days old, respectively. (Lurz, et al., 2005; Tacutu, et al., 2013; Thorington, Jr., et al., 2012; Wauters and Dhondt, 1989)
Females make a leaf nest, den cavity or burrow to raise their young, until the young are weaned a few weeks after birth. Once young are born, female body weight significantly affects young survival. The probability of an offspring's mortality increases greatly if their mother loses a significant amount of weight during lactation. (Lurz, et al., 2005; Thorington, Jr., et al., 2012; Wauters and Dhondt, 1989)
Currently, there is no information available regarding the lifespan of Japanese squirrels. However, their close relative, European red squirrels may live up to 12 years in the wild and up to 14.8 years in captivity. (Tacutu, et al., 2013)
Japanese squirrels are diurnal and active throughout the year. They are mostly solitary, but adults may nest together, especially in the winter. There is a social hierarchy among males and females, older, heavier individuals are more dominant. More dominant individuals usually have larger home ranges, but their size changes with food availability, season and sexual activity. Home ranges rarely overlap; scent marking, through urine and other secretions, denotes range. (Lurz, et al., 2005; Thorington, Jr., et al., 2012)
Female Japanese squirrels maintain an average home range size of 4.3 to 12.9 ha, as opposed to the male home range size of 5.6 to 40.3 ha. Woodlots inhabited by Japanese squirrels have an average size of 122.9 ha, ranging from 20.8 to 449.2 ha. Squirrels were not found in woodlots with an average size smaller than 12.6 ha. Japanese squirrels residing in fragmented forests typically have a much larger home range size. (Tamura, 2004)
Although information regarding the communication channels of Japanese squirrels is limited, information is available regarding their closest relatives, European red squirrels. These animals scent mark on branches and tree trunks within their home range using urine and secretions from glands on their chin. These markings are used to represent home range, status and reproductive condition. Most vocal communication is accompanied by specific body postures. Loud and soft chucking calls, explosive “wrruhh” sounds, moans and teeth chattering are all common sounds emitted by European red squirrels. Aggressive communication is seen during mating season including loud chucks, foot stamping and tail flagging; chasing is common during mating season as well. (Lurz, et al., 2005)
Japanese squirrels are primarily herbivorous and mostly eat seeds, buds, flowers and fruits, they may also consume insects and above ground fungi. Japanese walnuts make up a large portion of their diet as well. Among squirrels living in Karuizawa and Nagano Prefecture, Japanese walnuts make up about 35% of their annual diet. (Tamura, 2011; Thorington, Jr., et al., 2012)
Scatter-hoarding is performed by Japanese squirrels. In one study, Japanese squirrels hoarded 50.6% of 720 walnuts. Walnuts were cached at a distance of 0 to 168 meters. When given a variety of seed sizes, 90% of large seeds were hoarded compared to 60% of small seeds. Smaller seeds are eaten more readily, instead of hoarding. Seed size also determines how far the seed is cached from its original location. Large seeds have a mean transport distance of 16.5 m, where smaller seeds are only transported about 4 m. Smaller seeds are more likely to be hoarded arboreally, 56.8% of larger seeds are hoarded on the ground. (Tamura and Hayashi, 2008; Tamura, et al., 1999)
Japanese squirrels are predated upon by martens, foxes, domestic cats and dogs and some raptors and crows. It has been illegal for humans to hunt Japanese squirrels since 1994. If threatened, these squirrels climb to the opposite side of a tree from observers or predators, or freeze motionless on a branch or trunk. (Lurz, et al., 2005; Thorington, Jr., et al., 2012)
Although there is insufficient information about the ecosystem roles played by Japanese squirrels, there is information about tree squirrels in general. Tree squirrels are most commonly found in mature forests, which provide their needed food, nest cavities, cover and places for seed storage. Without these elements, squirrels cannot survive, which makes tree squirrels good indicators of forest health. This can be seen in studies involving Japanese squirrels. Kataoka and Tamura (2009) found that woodlots inhabited by squirrels averaged 122.9 ha, woodlots without squirrels averaged 12.6 ha, these smaller woodlots were neglected due to their lack of resources. If there are not enough resources for squirrels, there most likely are not enough resources for other animals as well. (Kataoka and Tamura, 2009; Koprowski, 2005)
There is currently no information regarding the economic importance of Japanese squirrels, however, European red squirrels are game animals hunted for fur in parts of Europe and Russia. Japanese squirrels could be used in a similar fashion because they are very close relatives. (Lurz, et al., 2005)
Japanese squirrels are not known to cause any negative economic impacts.
Due to urbanization and habitat fragmentation, Japanese squirrels have become extinct in Kyushu and threatened in other areas of Japan. (Kataoka and Tamura, 2009)
Based on genetic research of Old World Sciurus squirrels, Japanese squirrels and European red squirrels (Sciurus vulgaris) have the fewest genetic differences. European red squirrels are believed to have recently diverged to Japan and underwent a speciation event that lead to Japanese squirrels, although, juvenile European red squirrels have darker pelage. It is believed that European red squirrels and Japanese squirrels are conspecifics, meaning that they can interbreed, based on karotypes and ribosomal RNA genes. There are no known subspecies of Japanese squirrels. (Long, 2003; Lurz, et al., 2005; Oshida, et al., 2009)
Courtney McLive (author), Northern Michigan University, John Bruggink (editor), Northern Michigan University, Leila Siciliano (editor), Animal Diversity Web Staff.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
animals that live only on an island or set of islands.
a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).
having the capacity to move from one place to another.
an animal that mainly eats fungus
the area in which the animal is naturally found, the region in which it is endemic.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
places a food item in a special place to be eaten later. Also called "hoarding"
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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