Micromys minutusEurasian harvest mouse

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Geographic Range

M. minutus lives throughout Europe and northern Asia. Distribution ranges from northwest Spain through most of Europe, across Siberia to Korea, north to about 65 degrees in Russia, south to the northern edge of Mongolia. There are also isolated populations in southern China west through Yunnan. (Wilson 1993)

Habitat

M. minutus lives in tropical and subtropical regions and prefers habitats characterized by tall grasses. These would include high meadows, reed grass plots, bushland interspersed with grasses,and grain fields. In Italy and East Asia, they also make a home in rice fields. Population density may be very high in favorable environments. Originally, these mice lived in humid regions with high, long-lasting grasses growing near rivers, ponds, and lakes. With the advent of human encroachment, however, M. minutus has been forced to live along roadsides and in crop fields. When the farmer clears his land for the harvest, this mouse is left homeless. The problem is solved by the mouse either forming a shallow burrow in the soil, or finding shelter in the barn or silo. Not all mice are so lucky, however, and many mice die after being rendered homeless. (Grzimek 1990; Fact-File)

Physical Description

M. minutus a small mouse, ranging in size from 55 to 75 mm long, with a tail that is usually 50 to 75 mm long. It has large eyes and ears, which permits it to see the slightest motions and hear the faintest sounds in the darkness. It has a small, blunt nose encircled by vibrissae. The fur is soft and thick, with the upper parts of the body a brownish color with a yellowish or reddish tinge, and the under parts white to buffy colored. The prehensile tail is bicolored and lacks fur at the very tip, and the feet are fairly broad. The feet are specially adapted for climbing, with the outer of the five toes on each foot being large and more-or-less opposable. This mouse can grip a stem with each hindfoot and its tail, leaving the forepaws free for collecting food. It can also use its tail for balance as it scurries along long grass stems. The fur is somewhat thicker and longer in the winter than in the summer. As with other members of its subfamily, M. minutus has moderately low crowned teeth with rounded cusps on the biting surface arranged in three longitudinal rows. The masseter muscle, as well as the lateral muscle of the jaw, are moved forward on the maxillary, providing very efficient, effective gnawing action. The auditory bullae are large, and it is thought that the size of these resonating chambers enables the mouse to detect low frequency sounds carried over great distances, and thus be better able to escape predation. (Burton 1969; Grzimek 1990; Macdonald 1985; Nowak 1983)

  • Average mass
    6 g
    0.21 oz
    AnAge
  • Average basal metabolic rate
    0.201 W
    AnAge

Reproduction

The female gives birth to an average litter of 5 to 6 young after a gestation period of 21 days. Births take place in "high nests", structures built about 100 to 130 cm above the ground. Construction on these nests begins during the spring and summer breeding season, and one nest is built for each litter of young. These nests are globular in shape, about 60 to 130 mm in diameter. They are formed of three layers of grass blades woven tightly together. The lining consists of finely shredded leaves and grass, which form a soft warm nest for the young. There is often more than one entrance, but these holes are kept closed by the female during the first week after parturition, and males are not allowed into the nest at all. Reproduction is usually concentrated during warmer, drier months, starting around April and ending in September. Females are polyestrous, undergo a postpartum estrus, and under the correct favorable conditions, can give birth several times in rapid succession. Because they have a short natural longevity, females usually live through only one or two reproductive seasons in a lifetime, but in captivity they have been known to experience up to nine. Gestation is about 17-18 days, as is the typical minimum interval between litters. The number of young per litter ranges from 1 to 13, but is usually around 3 to 8. The young weigh about a gram at birth, and are 2 cm long. The young are born naked, blind and altricial, but can hold onto a grass stalk as early as three days after birth. They open their eyes at 8 to 10 days, are weaned and leave the nest at 15-16 days, and reach sexual maturity in 35 days. Maximum known longevity in the wild is 16 to 18 months, with few individuals living past 6 months. In captivity, M. minutus can live to be just under 5 years old. (Burton 1969; Grzimek 1990; Nowak 1993)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
    5.2
    AnAge
  • Average gestation period
    20 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    40 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    37 days
    AnAge

Lifespan/Longevity

Behavior

These tiny mice are moderately sociable. They live in small, overlapping home ranges. Population numbers fluctuate over the years and seasonally, generally peaking around autumn. While population density typically remains around 100 to 200 individuals per hectare, it has been observed that as many as 5,000 individuals may congregate in a barn or grain storage area during the winter. They merely tolerate each other at this time, becoming more agressive towrad one another as warm weather approaches. If captive males are placed together they will fight fiercely. Adults of opposite sexes come together only to mate and construct a breeding nest, then the female drives the male away. Nonbreeding individuals may also construct breeding nests, but they are less sturdy and lack the inner lining. During the cooler months, M. minutus may build a sleeping nest out of a mass of grass blades shredded lengthwise and laid on the ground or in a shallow burrow if it cannot find a more adequate shelter. This mouse does not hibernate. It is active in spurts of time throughout the day and night, with a three hourly rhythm of alternating sleeping and eating throughout each 24 hour day. Every third hour, it feeds for half an hour, while the rest of the time it spends sleeping. In order to escape enemies, M. minutus moves slowly, and incorporates "camouflage posture" as a defense, where it remains motionless against the stalk of the grass. If danger persists, the mouse lets itself drop into the darkness of the ground level. (Burton 1969; Grzimek 1990; Nowak 1983)

Communication and Perception

Food Habits

M. minutus eats a variety of seeds, especially grasses, fruit and grain. In the summer, its diet also contains insects and larvae, such as moths, caterpillars, and grasshoppers. It is a very opportunistic feeder and eats whatever is available during the season. In winter, when food is scarce, M. minutus takes advantage of human stores of food and is often found in grain silos or haystacks. In order to facilitate cellulose digestion, these rodents have a large cecum which contains large amounts of bacteria. After the food has been softened and partially digested in the stomach, it passes down through the large intestine and into the cecum, There the cellulose is broken down into digestable carbohydrate constituents. However, absorption can only take place higher in the gut and in the stomach. For this reason, rodents reingest the soft pellets of bacterially digested food after having defecated it. This reingestion allows the digestive system to be highly efficient, assimilating 80 percent of the ingested energy. (Fact-File; Grzimek 1990; Macdonald 1985; Nowak 1983)

Economic Importance for Humans: Positive

In the wild, M. minutus helps keep populations of crop pests down to a manageable level. (Fact-File; Macdonald 1985)

Economic Importance for Humans: Negative

M. minutus consume large amounts of crop yields, either by eating the seeds in the field or feeding on carefully stored grains. Rodent-borne diseases have also been a large influence on the human population, taking more human lives than all wars and revolutions put together. (Macdonald 1985)

Conservation Status

Although not endangered, numbers of M. minutus have been greatly reduced by modern agricultural methods, such as combine harvesting, spraying, earlier harvesting, and stubble burning. They also seem to have a three-year pattern of population increase and decline. Every third year, the population apparently crashes, only to be rebuilt over the next two years. It is unclear why this happens. (Burton 1969; Fact-File; Macdonald 1985)

Contributors

Francesca Ivaldi (author), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

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.

chemical

uses smells or other chemicals to communicate

endothermic

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.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Burton, Dr.M., R. Burton. ed. 1969. The International Wildlife Encyclopedia. Vol 8. Marshall Cavendish Co., N.Y.

Fact-File information cards

Grzimek. 1990. Encyclopedia of Mammals. Vol 3. McGraw-Hill Publishing Co., N.Y.

Macdonald, Dr.D. ed. 1985. Encyclopedia of Mammals. Facts on File Publisher, N.Y.

Nowak, R., J. Paradiso. ed. 1983. Walker's Mammals of the World. Vol 2. 4th ed. Johns Hopkins University Press, Baltimore.

Wilson, D.E., D.M. Reeder. ed. 1993. Mammal Species of the World 2nd ed. Smithsonian, Washington.