This includes but is not limited to mice, rats, voles, moles. Mice reproduce every 20 – 30 days and produce an average litter size of 10 – 12 pups. Rats reproduce every 30 – 40 days and produce and average litter size of 6 – 13 pups.
Mice: Mice are a small mammal belonging to the order of rodents, characteristically having a pointed snout, small rounded ears, a body-length scaly tail and a high breeding rate. The best known mouse species is the common house mouse (Mus musculus). It is also a popular pet. In some places, certain kinds of field mice are also common. They are known to invade homes for food and occasionally shelter. Breeding onset is at about 50 days of age in both females and males, although females may have their first estrus at 25–40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4–5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating. Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the estrous cycle is known as the Whitten effect. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the Bruce effect. The average gestation period is 20 days. A fertile postpartum estrus occurs 14–24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3–10 days owing to delayed implantation. The average litter size is 10–12 during optimum production, but is highly strain-dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh 0.5–1.5 g (0.018–0.053 oz) at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 10–12 g (0.35–0.42 oz). If the postpartum estrus is not utilized, the female resumes cycling 2–5 days post-weaning. Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.
Rats: Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. “True rats” are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus. Many members of other rodent genera and families are also referred to as rats, and share many characteristics with true rats. Rats are typically distinguished from mice by their size. Generally, when someone discovers a large muroid rodent, its common name includes the term rat, while if it is smaller, the name includes the term mouse. The muroid family is broad and complex, and the common terms rat andmouse are not taxonomically specific. Scientifically, the terms are not confined to members of the Rattus and Mus genera, for example, thepack rat and cotton mouse.
Voles: Voles are small rodents that grow to 3–9 in (7.6–22.9 cm), depending on the species. They can have five to 10 litters per year. Gestation lasts for three weeks and the young voles reach sexual maturity in a month. As a result of this biological exponential growth, vole populations can grow very large within a very short period of time. Since litters average five to 10 young, a single vole can birth a hundred more voles in a year. Voles are commonly mistaken for other small animals. Moles, gophers, mice, rats and even shrews have similar characteristics andbehavioral tendencies. Since voles will commonly use burrows with many exit holes, they can be mistaken for gophers or some kind of ground squirrel. Voles thrive on small plants yet, like shrews, they will eat dead animals and, like mice or rats, they can live on almost any nut or fruit. Additionally, voles will target plants more than most other small animals, making their presence evident. Voles will readily girdle small trees and ground cover much like a porcupine. This girdling can easily kill young plants and is not healthy for trees or other shrubs. Voles will often eat succulent root systems and will burrow under plants or ground cover and eat away until the plant is dead. Bulbs in the ground are another favorite target for voles; their excellent burrowing and tunnelling skills give them access to sensitive areas without clear or early warning. The presence of large numbers of voles is often only identifiable after they have destroyed a number of plants. However, like other burrowing rodents, they also play beneficial roles, including dispersing nutrients throughout the upper soil layers.
Mole: Moles are small cylindrical mammals adapted to a subterranean lifestyle. They have velvety fur; very small, difficult to see ears and eyes, reduced hindlimbs; and short, powerful forelimbs with large paws well-adapted for digging. The term “mole” is especially and most properly used for “true moles” of the Talpidae family in the order Soricomorpha found in most parts of North America, Asia, and Europe although may refer to other completely unrelated mammals of Australia and southern Africa which have also evolved the mole body plan; it is not commonly used for some talpids, such as desmans and shrew-moles, which do not quite fit the common definition of “mole”. Breeding season for a mole depends on species but is generally February through May. Males search for females by letting out high-pitched squeals and tunneling through foreign areas. The gestation period of the Eastern (US) mole (Scalopus aquaticus) is approximately 42 days. Three to five young are born, mainly in March and early April. Pups leave the nest 30–45 days after birth to find territories of their own.