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Coues's rice rat

Oryzomys couesi

What do they look like?

Coues' rice rats are small rodents that look like rats. They are usually 242 to 265 mm long, and weigh 42 to 83 g. They look a lot like marsh rice rats, but they are bigger and less gray. They are covered in brown fur on top. Their fur is lighter on their legs, faces, and sides. They have a layer of underfur on their backs that is soft, thick, and repels water. Males are a little bit bigger than females. Their skulls are light and thin. Their skulls are different from marsh rice rats because their upper molars have three rows of bumps instead of two. (Goldman, 1918; Vega, et al., 2007; Wolfe, 1982)

  • Sexual Dimorphism
  • male larger
  • Range mass
    42 to 83 g
    1.48 to 2.93 oz
  • Range length
    242 to 265 mm
    9.53 to 10.43 in

Where do they live?

Coues’ rice rats live in the southeastern United States, and throughout Mexico and Central and South America. They also live on some nearby islands. Their spread across the United States is limited by the way water is managed for farming in southern Texas. (Alvarez-Castaneda, 1994; Merriam, 1901; Vega, et al., 2007)

What kind of habitat do they need?

Coues’ rice rats live mostly on land in grassy swamps or marshes along the coasts. They are good swimmers and divers who go underwater to escape, hunt, and find food. They may also live in high mountains nearby. (Benson and Gehlbach, 1979; Cook, et al., 2001; Goldman, 1918)

  • Range elevation
    0 to 1534 m
    0.00 to 5032.81 ft
  • Average elevation
    823 m
    2700.13 ft

How do they reproduce?

Coues' rice rats can reproduce any time during the year when there are good spots available to nest. This means their reproduction probably depends on their numbers and their environment. Females give birth to 2 to 7 young at a time, and usually around 4. They grow inside the bodies of their mothers for 21 to 28 days before they are born. If the conditions of the environment are right, females have 5 to 6 groups of young in the same year. Most of this happens between January and May. The young are born naked and blind, and weigh about 3 g each. They open their eyes on day 5 or 6 and drink milk from their mothers until around day 11. They are able to have their own young after 40 to 45 days. They reach their adult size of 48 g when they are about 9 months old. (Benson and Gehlbach, 1979; Cook, et al., 2001; Vega, et al., 2007; Wolfe, 1982)

  • How often does reproduction occur?
    Coues' rice rats breed throughout the year.
  • Breeding season
    Most reproduction occurs from January to March.
  • Range number of offspring
    2 to 7
  • Average number of offspring
  • Range gestation period
    21 to 28 days
  • Range weaning age
    5 to 6 minutes
  • Range age at sexual or reproductive maturity (female)
    40 to 45 days
  • Range age at sexual or reproductive maturity (male)
    40 to 45 days

Females protect their young in nests made from plants found nearby. Mothers feed the young milk from their bodies until they are about 11 days old. (Benson and Gehlbach, 1979; Wolfe, 1982)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

How long do they live?

The longest life of a Coues' rice rat was recorded to be 599 days. Males usually live about 165 days and females usually live about 167 days. (Clark, 1980)

  • Average lifespan
    Status: wild
    700 days
  • Average lifespan
    Status: captivity
    599 days
  • Average lifespan
    Status: captivity
    165 days

How do they behave?

Like other rice rats, Coues' rice rats are very active, social, and active at the night. They build nests from plants they find nearby in their marshy habitat. They are good at swimming and diving, and move their tails back and forth when they swim. This helps keep them balanced, and is good for finding food and getting away from predators. They can swim underwater farther than 10 m. They spend a lot of time cleaning and grooming themselves, which helps make sure their fur keeps repelling water. (Cook, et al., 2001; Wolfe, 1982)

Home Range

Scientists don't know the size of the area where Coues' rice rats live. Their close relatives marsh rice rats usually live in an area that is .37 ha for males or .23 ha for females. (Wolfe, 1982)

How do they communicate with each other?

Coues' rice rats probably communicate and get information about their environment in similar ways to other rice rats. This means they use their senses of sight, hearing, taste, and smell. They also use these same senses to communicate. When they are put into new environments in a laboratory, they use their noses and explore. (Wolfe, 1982)

What do they eat?

Coues' rice rats are omnivores, so they eat both animals and plants. Some older scientific studies reported that they eat mostly seeds and parts of succulent plants, that they like grass stems in meadows, and that they eat meat as well. Later scientific studies reported that their diet changes depending on the season. These studies said that they eat about the same amount of plant and animal foods. The animal foods they eat most were insects and snails. They also eat fish, deer mice, and sparrows. Coues' rice rats store food to eat later. (Goldman, 1918; Wolfe, 1982)

  • Animal Foods
  • birds
  • fish
  • eggs
  • insects
  • mollusks
  • Plant Foods
  • leaves
  • seeds, grains, and nuts

What eats them and how do they avoid being eaten?

A common predator of rice rats is boa constrictors, which affect the number of them in Central and South America. They are also an important food source for barn owls. Their close relatives, marsh rice rats, are most often eaten by owls. Rice rats are most often eaten by hawks, owls, cottonmouths and water snakes. Other predators include raccoons, red foxes, barred owls, minks, weasels, and skunks. (Vega, et al., 2007; Wolfe, 1982)

What roles do they have in the ecosystem?

Coues' rice rats get infected with parasites like mites and ticks , lice, fleas, digeneans, pentastomids, and coccidians. (Wolfe, 1982)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • mites and ticks (Acari)
  • lice (Phthiraptera)
  • fleas (Siphonaptera)
  • flatworms (Digenea)
  • tongue worms (Pentastomida)
  • internal parasites (Isospora)

Do they cause problems?

Coues' rice rats could spread human diseases. They get parasites like mites and ticks, fleas, and lice that could transfer to other animals or to humans. They have been infected with a kind of flukes from eating killifishes. They also have a kind of dental disease that scientists are researching. (Wolfe, 1982)

How do they interact with us?

Coues' rice rats don't have any known positive impacts on humans. They don't interact much with humans because they usually are found in swampy and marshy areas where humans don't usually live. (Goldman, 1918)

Are they endangered?

Coues' rice rats are not endangered. They are most threatened by construction of roads taking over and disturbing their habitat. (Fuentes-Montemayor, et al., 2009)


Natalie Nguyen (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Catherine Kent (editor), Special Projects.


Alvarez-Castaneda, S. 1994. Current status of the rice rat, Oryzomys couesi peninsularis. Southwestern Naturalist, 39(1): 99-100.

Benson, D., F. Gehlbach. 1979. Ecological and Taxonomic Notes on the Rice Rat (Oryzomys couesi) in Texas. Journal of Mammology, 60(1): 225-228.

Clark, D. 1980. Population Ecology of an Endemic Neotropical Island Rodent: Oryzomys bauri of Santa Fe Island, Galapagos, Ecuador. Journal of Animal Ecology, 49(1): 185-198.

Cook, W., R. Timm, D. Hyman. 2001. Swimming ability in three Costa Rican dry forest rodents. Revista de Biología Tropical, 49(3-4): 1177–1181.

Dewsbury, D. 1970. Copulatory Behavior of Rice Rats (Oryzomys palustris). Animal Behavior, 18: 266-275.

Fuentes-Montemayor, E., A. Cuarón, E. Vázquez-Domínguez, J. Benítez-Malvido, D. Valenzuela-Galván. 2009. Living on the edge: roads and edge effets on small mammal populations. The Journal of Animal Ecology, 78(4): 857-865.

Goldman, E. 1918. The rice rats of North America. Washington: North American Fauna.

Merriam, C. 1901. Synopsis of the rice rats (genus Oryzomys) of the United States and Mexico. Washington, D.C.: Washington Academy of Sciences.

Schnell, G., M. de Lourdes Romer-Almaraz, S. Martinez-Chapital, C. Sanchez-Hernandez, M. Kennedy. 2010. Habitat use and demographic characteristics of the west Mexican cotton rat (Sigmodon mascotensis). Mammalia, 74(4): 379-393.

Vazques-Domingues, E., R. Vega, A. Cuaron. 2007. Genetic Variability and Population Structure of an Island Endemic Rodent (Oryzomys couesi cozumelae): Conservation Implications. 2007 International Summit on Evolutionary Change in Human-altered Environments.

Vega, R., E. Vázquez-Domíngueza, A. Mejía-Puentea, A. Cuarón. 2007. Unexpected high levels of genetic variability and the population structure of an island endemic rodent (Oryzomys couesi cozumelae). Biological Conservation, 137(2): 210-222.

Wolfe, J. 1982. Oryzomys palustris. Mammalian Species, 176: 1-5.

University of Michigan Museum of ZoologyNational Science Foundation

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Nguyen, N. 2013. "Oryzomys couesi" (On-line), Animal Diversity Web. Accessed February 22, 2024 at

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