Marsh rice rat (Oryzomys palustris)

Marsh rice rat in grass
IUCN Red List species status – Least Concern LEAST

Top facts

  • A prolific breeder, the female marsh rice rat can become pregnant on the same day as it gives birth.
  • The genus name of the marsh rice rat, Oryzomys, comes from two Greek words meaning, ‘rice mouse’, while the species name, palustris, is Latin for marshy.
  • An opportunistic feeder, the marsh rice rat eats anything from seeds to baby turtles.
  • A skilled swimmer, the marsh rice rat can swim underwater for up to ten metres at a time.
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Marsh rice rat fact file

Marsh rice rat description

GenusOryzomys (1)

The name of the genus to which the marsh rice rat (Oryzomys palustris) belongs comes from two Greek words ‘oryza’, meaning rice, and ‘mys’, meaning mouse. The second part of its scientific name, ‘palustris’, is Latin for marshy (4).

The marsh rice rat is grey-brown on the upperside, and has a lighter, grey-white underside (4) and white feet (3) (4) (5). The fur is coarse and long (5) and has a dense, water-repellent underlayer (2) (4). The rounded, leaf-like ears are also furred (5). The marsh rice rat’s dark brown tail is slightly lighter on the lower surface (4) and is usually shorter in length than the body and head combined (3), although it may be of equal length (5). The tail usually only has very few hairs on its surface (5).

The male and female marsh rice rat are similar in size and colour (3) (4).

There are six recognised subspecies of marsh rice rat: Oryzomys palustris palustris, Oryzomys palustris coloratus, Oryzomys palustris natator, Oryzomys palustris planirostris, Oryzomys palustris sanibeli and Oryzomys palustris texensis. The subspecies differ in their size, colouration and distribution (2).

Marsh oryzomys.
Un Ratón Arrozalero.
Total length: 22.6 - 30.5 cm (2)
Head-body length: 11 - 13 cm (3)
Adult weight: 45 - 80 g (2)

Marsh rice rat biology

The marsh rice rat is thought to breed year-round (1) (2), although in the more northerly areas of its range, breeding may be seasonal (3). A prolific breeder (5), the female is able to produce up to eight litters per year (5). After a gestation period of 21 to 28 days (1) (2) (3), the female will usually give birth to between 4 and 6 young (1), although litters containing as many as 7 have been reported (1) (5). The nest of the marsh rice rat is a spherical, grapefruit-sized structure (2) (4) (5), which is made of loosely woven dried grass or sedge and is usually placed at the base of a shrub (2) (4). The young are weaned 2 weeks after birth (1), and become sexually mature after 50 to 60 days (2) (3) (5). The female is able to become pregnant again immediately after giving birth (4) (5).

The primarily nocturnal marsh rice rat (1) (2) (4) is active year-round and does not hibernate (4). Both the male and female establish a home range, although the male will usually occupy a larger area (2). A rather cleanly species, the marsh rice rat creates ‘latrine sites’ outside of its burrow where it goes to defecate, and spends a large amount of time grooming itself, which is thought to help keep its pelage water repellent (4). A semi-aquatic species (2), it is a skilled swimmer (5), and it is known to regularly swim underwater for distances of over ten metres (2), using its feet to propel it through the water (4).

A generalist and opportunistic feeder, the marsh rice rat eats a wide range of prey items (4), with seeds and succulent vegetation taken for the majority of the year, which are supplemented with insects, crabs, snails (2) (4), young turtles (3) (4), fish and carrion (2) (3), as well as the eggs and young of birds (4) (5). The diet of an individual is seasonally variable and will generally depend on what is available nearby (4).


Marsh rice rat range

The marsh rice rat is found in the south-eastern quadrant of the United States (5), from Texas, Oklahoma and Kansas in the west to Florida, North Carolina and New Jersey in the east (1) (2) (4) (5).


Marsh rice rat habitat

As its name suggests, the marsh rice rat inhabits various wetlands, including marshes, swamps (1) (2) (4) (5) and wet meadows (1) (2) (5), which may be located around fresh or saltwater (1) (5). In favourable areas, individuals of this species may establish an extensive network of subterranean tunnels (4). During high tides, the marsh rice rat may take refuge in wetlands at higher elevations (1).


Marsh rice rat status

The marsh rice rat is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Marsh rice rat threats

Although there are not thought to be any major threats to the marsh rice rat (1), certain populations are threatened by habitat loss due to land drainage and reclamation for the construction of industrial complexes (4). The marsh rice rat population in the Florida Keys is thought to have been greatly reduced due to habitat loss (5). Individuals living in distinct populations may also be vulnerable to natural disasters, low genetic diversity levels and high mortality rates (6).


Marsh rice rat conservation

Although there are not currently any conservation measures in place for the marsh rice rat, many suggestions have been made for the future, including research on its exact distribution, assessing the amount of suitable habitat within its range and monitoring wild populations. In Illinois, this species is listed as threatened (6), and the population in the lower Florida Keys has been listed as endangered by the U.S. Fish and Wildlife Service (5). The species itself may not be protected throughout most of its range, but it does occur in several protected areas, safeguarding certain populations against habitat loss (1).


Find out more

Find out more about the marsh rice rat:

Find out more about the conservation of North American rodents:

  • Hafner, D.J., Yensen, E. and Kirkland Jr, G.L. (1998) North American Rodents: Status Survey and Conservation Action Plan. IUCN/SSC Rodent Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:


This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



The flesh of a dead animal.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
The state of being pregnant; the period from conception to birth.
A winter survival strategy in which an animal’s metabolic rate slows down and a state of deep sleep is attained. While hibernating, animals survive on stored reserves of fat that they have accumulated in summer.
Home range
The area occupied by an animal during routine activities, which is not actively defended.
Active at night.
The coat of a mammal, composed of fur, hair or wool.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
Living underground, in caves or groundwater.
In plants, species with thick, fleshy, water-storing stems and leaves.


  1. IUCN Red List (January, 2014)
  2. Wolfe, J.L. (1982) Oryzomys palustris. Mammalian Species, 176: 1-5. Available at:
  3. Hoffmeister, D.F. (1989) Mammals of Illinois. University of Illinois Press, Champaign, Illinois.
  4. Merritt, J.F. (1987) Guide to the Mammals of Pennsylvania. University of Pittsburgh Press, Pittsburgh, Pennsylvania.
  5. Brown, L.N. (1999) A Guide to the Mammals of the Southeastern United States. University of Tennessee Press, Knoxville, Tennessee.
  6. Hellgren, E.C., Nawrot, J.R. and Eubanks, B. (2009) Status Review and Recovery Outline: Marsh Rice Rat - Oryzomys palustris. Illinois Department of Natural Resources, Illinois. Available at:

Image credit

Marsh rice rat in grass  
Marsh rice rat in grass

© Philip C Stouffer

Philip C Stouffer


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