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The house mouse (Mus musculus, Mus domesticus) belongs to the family Muridae of the order Rodentia. Examples of other rodents are squirrels, ground hogs, hamsters, and voles. The Roof rat and Norway rat belong to the same family as the house mouse. All rodents are characterised by two pairs of incisors growing for life. |
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Successful Colonisation
The global colonisation of the House Mouse as a commensal species can be attributed to its adaptable behaviour, to its omnivorous feeding habits, its ability to live in a wide variety of environments, to its small size, and high reproductive potential. There was not much need for active dispersal; the mouse was distributed with stored products and packaging materials, such as bags and cartons, across the oceans. It is supposed that house mice arrived in Europe from North Africa, through Spain, when agriculture was established. House mice have a peridomestic existence in the temporate zone, in close proximity to man, livestock, stored food and trading merchandise. |
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Identification
Size: The head-body length of an adult mouse does not exceed 10cm. The tail is roughly the same length as the body, and is almost completely hairless with up to 200 scaled rings.
Appearance: The appearance of mice are small, agile and furry, which often causes disgust. Their fur is light to dark grey or yellowish above, with gradual transition to the grey or brownish belly. Their ears are relatively large in comparison to the size of their body, and their eyes appear small. Often they can be identified by their stale smell, which can be detected by entering an infested room. Mice have well developed feet for climbing on almost every surface. |
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Food
Mice are essentially herbivores, and seeds are their prevalent food. Often oily seeds, such as sunflower seeds are preferred. Invertebrates, including beetles, spiders and larvae, fruits, and even con-specifics may be eaten under certain circumstances. House mice need to drink only if they exclusively consume dry food, such as grain or dry animal feed. Mice can live and breed without drinking water as long as their diet has a water content of at least 15%. Under laboratory conditions, adult mice consume an average of 3.5g of dry food (i.e. cereals) per day. Under field conditions, consumption may be higher. In addition, there is a considerable loss of food by spillage, because mice are wasteful eaters, and often discard and spoil more than they eat. |
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Reproduction
Period: House mice reproduce all year round inside buildings if sufficient food is available, also in buildings without heating and in stables and barns. Outdoor living mice reproduce seasonally like most mammals, from May to October.
Intensity: The number of young in one litter ranges from 1 to 12. The average litter size is around 5 to 8. The number of pups per litter is lower at the beginning and at the end of the reproductive period in outdoor living mice. In commensal mice, there is almost no variation. The proportion of pregnant females depends on population–density and decreases during adverse conditions. At low population densities, the proportion of pregnant females can be up to 51%, and decreases below 30% at high densities. A female is theoretically capable of producing as many as ten litters under favourable environmental conditions.
Regulation: The intensity of reproduction depends upon environmental conditions, such as availability of food, nesting sites and nesting materials, and general stress. If the female is in poor condition, or under crowded conditions, one or more embryos may be resorbed at an early stage. This can also be the case when the dominant male is replaced, thereby reducing stress for the female and allowing immediate reproduction of the new dominant male (Bruce effect).
Biology: Female mice become reproductively mature at 35 – 40 days of age. They come into oestrous for 1 – 2 days within cycles of 4 – 14 days. (Oestrus = when females are receptive to being mated.) A vaginal plug is built after copulation, finishing the mating period. The gestation period is 19 – 21 days. Immediately after giving birth, females come into oestrous again. Therefore lactating females may be pregnant already. |
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Life-span
Only one half of a litter survives until the young reach independence. Monthly mortality of adult mice is at 20%. Mortality during winter can reach up to 90% in outdoor living mice. The maximum recorded age of a wild mouse was 20 months. The average life-span of mice living in buildings ranges from 3 to 6 months. |
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Habitat Use
Ability to Move: Mice have the ability to climb, jump, swim, and dig. They can jump up to 50cm high or down from a height of 2 metres without injury. Mice are also able to climb almost any surface, they only need some texture or cables, pipes etc., they can grab onto. They can squeeze through openings and slots smaller than 1cm.
Home range: In contrast to Norway rats, the home range of mice is three-dimensional: Burrows and pathways are often located overhead in walls, roofs, insulation materials and devices. The ground occupied by a mouse family therefore may be only a few square metres. To run longer distances, mice frequently use fixed paths, such as on water pipes and power cables. |
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Behaviour
Activity: Generally, mice are nocturnal animals; approximately 90% of their activity occurs during darkness, but they may adapt their activity to local conditions, such as availablility of food, population density, and illumination. Activity peaks are at dusk and before dawn.
Nesting behaviour: Mice need dry and well protected places for nesting. They find such places in buildings, i.e. in walls, roof voids and insulation layers. Even cavities in machines and electric devices are used. Materials found in their vicinity like feathers, paper, hair etc. are often used for nest construction. Damage to cardboard boxes and other packaging is often the consequence. Often one nest harbours different litters of different ages of several dams. If one dam gets lost (i.e. as victim of pest control), others will replace it and care for the orphans.
Social Structure: House mice live in small groups with highly structured social hierarchy. One male dominates the other males of a group. The dominant male contributes more to reproduction within its group than subordinate males. Pregnant and lactating females, as well as dominant males are most aggressive against mice of other groups.
Orientation: Smell is the most important sense of mice for orientation. Animals identify their group, and probably individuals by smell. Urine marking is used to define territories and pathways. After some time, such pathways can be identified by a brown, sticky layer of urine smears and dust. Urine marks can be well seen at dark using ultraviolet light.
Communication: Besides olfactory cues, acoustic communication plays an important role during social interactions in mice groups. Different acoustic signals are given during social encounters, such as aggressive interactions and mating, providing information on the social status and intention of the animal. Some of these calls are ultrasonic, in particular those produced by young, which motivate the dam to look for them. |
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Diseases
Like other wild rodents, populations of mice are exposed to a wide range of parasites and diseases. Widespread parasites are fleas, which generally are species-specific, but occasionally parasitise man. Infections are common with bacteria like Streptobacillus (i.e. S. moniliformis), Streptococcus, and Salmonella. Many of these pathogens are also harmful to livestock and man, and therefore are not tolerated in livestock farming and in the food production chain. |
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