house mouse

Appearance

House mice have an adult body length of 7.5–10 cm and a tail length of 5–10 cm . The weight is typically 10–25 g . They vary in colour from white to grey, and light brown to black. They have short hair and a light belly. The ears and tail have little hair. The hind feet are short compared to ''Apodemus'' mice, only 15–19 mm long; the normal gait is a run with a stride of about 4.5 cm , though they can jump vertically up to 45 cm . The voice is a high-pitched squeak. House mice thrive under a variety of conditions: they are found in and around homes and commercial structures as well as in open fields and agricultural lands.


Young males and females are not easily distinguished: like people, females have a significantly smaller distance between their anus and genital opening. Females have 5 pairs of mammary glands and nipples; males have no nipples. When sexually mature, the most striking and obvious difference is the presence of testicles on the males. These are large compared to the rest of the body and can be retracted into the body. In addition to the regular pea-size thymus organ in the chest, house mice have a second functional pinhead-size thymus organ in the neck next to the trachea.

Naming

There are three widely accepted subspecies, increasingly treated as distinct species:
⤷  ''Mus musculus castaneus''
⤷  ''Mus musculus domesticus''
⤷  ''Mus musculus musculus''

Two additional subspecies have been more recently recognized:
⤷ ''Mus musculus bactrianus''
⤷ ''Mus musculus gentilulus''

Many more names have been given to house mice, but are now regarded as synonyms of other subspecies. Some populations are hybrids of different subspecies, including the Japanese house mouse .Gough Island in the South Atlantic is used by 20 species of seabird for breeding, including almost all of the world's Tristan Albatross and Atlantic Petrel . Until house mice arrived on the island in the 19th century with seamen, the birds did not have any mammalian predators. The mice have since grown unusually large and have learned to attack albatross chicks, which can be nearly one metre tall but are largely immobile, by working in groups and gnawing on them until they bleed to death. The estimated 700,000 mice on the island kill a total of over one million bird chicks per year.

Behavior

House mice usually run, walk, or stand on all fours, but when eating, fighting, or orienting themselves, they stand only on the hind legs, supported by the tail. When they run, the horizontal tail serves for balance; the end stands up vertically, unless the mouse is frightened. Mice are good jumpers, climbers, and swimmers.

Mice are mostly active during dusk or night; they do not like bright lights. They live in a wide variety of hidden places that are near food sources and construct nests from various soft materials. Mice are territorial, and one dominant male usually lives together with several females and young. Dominant males respect each other's territory and normally enter another's territory only if it is vacant. If two or more males are held together in a cage, they will often turn aggressive unless they have been raised together from birth.

House mice primarily feed on plant matter but are omnivorous. They will eat their droppings to acquire nutrients produced by bacteria in their intestines. House mice, like most other rodents, do not vomit.

Mice are afraid of rats, which often kill and eat mice. This rat behaviour is known as muricide. Despite this behaviour free-living populations of rats and mice do exist together in forest areas in New Zealand, North America and elsewhere. House mice are generally poor competitors and in most areas cannot survive away from human settlements in areas where other small mammals, such as wood mice, are present. However, in some areas , mice are able to co-exist with other small rodent species.Female house mice have an estrous cycle that is 4–6 days long, with estrus itself lasting less than a day. If several females are held together under crowded conditions, they will often not have an estrus at all. If they are then exposed to male urine, they will become estrous after 72 hours.

Male house mice court females by emitting characteristic ultrasonic calls in the 30 kHz–110 kHz range. The calls are most frequent during courtship when the male is sniffing and following the female; however, the calls continue after mating has begun at which time the calls are coincident with mounting behaviour. Males can be induced to emit these calls by female pheromones. The vocalizations appear to be different in different individuals and have been compared to birdsongs because of their complexity. While females have the capability to produce ultrasonic calls, they typically do not do so during mating behaviour.

Following copulation, female mice will normally develop a copulation plug which prevents further copulation. This plug stays in place for some 24 hours. The gestation period is about 19–21 days, and they give birth to a litter of 3–14 young . One female can have some 5–10 litters per year, so the mice population can increase very quickly. Breeding occurs throughout the year . The newborn are blind and without fur. Fur starts to grow some three days after birth and the eyes open one to two weeks after birth. Males reach sexual maturity at about 6 weeks and females at about 8 weeks, but both can breed as early as five weeks.

Reproduction

Female house mice have an estrous cycle that is 4–6 days long, with estrus itself lasting less than a day. If several females are held together under crowded conditions, they will often not have an estrus at all. If they are then exposed to male urine, they will become estrous after 72 hours.

Male house mice court females by emitting characteristic ultrasonic calls in the 30 kHz–110 kHz range. The calls are most frequent during courtship when the male is sniffing and following the female; however, the calls continue after mating has begun at which time the calls are coincident with mounting behaviour. Males can be induced to emit these calls by female pheromones. The vocalizations appear to be different in different individuals and have been compared to birdsongs because of their complexity. While females have the capability to produce ultrasonic calls, they typically do not do so during mating behaviour.

Following copulation, female mice will normally develop a copulation plug which prevents further copulation. This plug stays in place for some 24 hours. The gestation period is about 19–21 days, and they give birth to a litter of 3–14 young . One female can have some 5–10 litters per year, so the mice population can increase very quickly. Breeding occurs throughout the year . The newborn are blind and without fur. Fur starts to grow some three days after birth and the eyes open one to two weeks after birth. Males reach sexual maturity at about 6 weeks and females at about 8 weeks, but both can breed as early as five weeks.