This article, by Jerry Cates (initiating author) and Adette Quintana (editor and contributing biologist) was begun on 13 November 2020, first published on 14 November 2020, and last revised on 18 January 2021. © Bugsinthenews Vol. 21:11(02).
As described in more detail elsewhere, North America hosts three species of commensal rodents. These are, specifically, the common house mouse (Mus musculus Linnaeus, 1758), the black or roof rat (Rattus rattus Linnaeus, 1758), and the brown or Norway rat (Rattus norvegicus Berkenhout, 1769).
Here we discuss the biological metrics that apply to each of these commensal rodents, particularly as measurements of physical and morphological attributes, and of food and water consumption.
The Common House Mouse (Mus musculus Linnaeus, 1758):
The adult common house mouse weighs between 13-30 grams, has a body length of between 2.5-3.75 inches, and a tail approx. 3.75 inches long. This rodent’s average daily food consumption varies from 2-4 grams, and its daily water intake varies from little to 6mL. Mouse water intake can be by direct or indirect means. Their food’s moisture content supplies some or most of their water needs. Because they naturally concentrate their urine, the need for free water intake is reduced. Thus, mice feeding on seeds with 12% protein or less survive entirely without free water, but if feeding on seeds with more than 12% protein must ingest from 3-13 g of free water daily.
House mice generally forage and nest within a home range having a diameter of 6-30 feet. This home range can expand to as much as 100ft or more as dictated by availability of food sources. When conditions encourage or demand dispersal, house mice tend to disperse within 30-300 meters of their previous nests, but may travel up to 1.25 miles when conditions dictate.
Female house mice attain sexual maturity in 6-10 weeks, and have a breeding potential of 6-10 litters over a lifespan of 1-2 years. Gestation takes 18-21 days, and litter sizes generally range from 5-8 pups, but can be as high as 13. Pups wean in about 21 days.
House mice are terrestrial, communal and territorial. They are colorblind and, in general, their visual faculties are limited. Though commensally associated with humans for the past 8,000+ years, feral populations are not unusual and, in cultivated fields, they may be the most abundant mammal observed. They are nervously active, good swimmers for short distances, and agile jumpers and climbers.
Pheromones drive most of their behavior. Their societies conform to a strict hierarchy, and they aggressively defend their communal and sub-communal territories. Females with newborns aggressively defend their pups and the familial territories they establish within the commune.
Exogenous plasticity, wherein behavior is decoupled from genetics, is highly developed in the house mouse. This enables the species to adapt quickly to novel environments. For example, though nocturnal, they are easily adaptable to environments with constant lighting.
The Black or Roof Rat (Rattus rattus Linnaeus, 1758):
The adult black or roof rat weighs between 150-250 grams, has a body length of between 5-8 inches, and a tail 6-9 inches long. This rodent’s average daily food consumption varies from 7-15 grams, and its daily water intake varies from 29-59mL.
Black/Roof rats generally forage and nest within a home range having a diameter of 25-100 feet. This home range can expand to as much as 500ft or more as dictated by availability of food sources. When conditions encourage or demand dispersal, black/roof rats tend to disperse within 50-500 meters of their previous nests, but may travel up to 3 miles if necessary.
Female black/roof rats attain sexual maturity in 12-16 weeks. They have a breeding potential of 3-4 litters over a lifespan of 5-18 months (average), Under optimal conditions the lifespan of the black/roof rat can extend to as much as 3 years. Gestation takes about 23 days, and litter sizes generally range from 4-8 pups. Pups wean in 28-35 days.
The Brown or Norway Rat (Rattus norvegicus Berkenhout, 1769):
The adult brown or Norway rat weighs between 340-500 grams, has a body length of between 6-11 inches, and a tail 4-9 inches long. This rodent’s average daily food consumption varies from 15-30 grams, and its daily water intake varies from 30-50mL.
Brown/Norway rats generally forage and nest within a home range with a diameter of 25-100 feet. This home range may extend to as much as 500ft or more as dictated by availability of food sources. When conditions encourage or demand dispersal, brown/Norway rats may travel up to 4 miles to find suitable habitat and food sources.
Female brown/Norway rats attain sexual maturity in 8-12 weeks, and have a breeding potential of 4-6 litters over a lifespan of 6-12 months (average). Under optimal conditions the lifespan of the brown/Norway rat may extend to as much as 3 years. Gestation takes about 22 days, and litter sizes generally range from 8-9 pups, but can range as high as 14. Pups wean in 20-29 days.
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