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Oryzomys couesiCoues's rice rat

By Natalie Nguyen

Geographic Range

Coues’ rice rats are found in the southeastern United States, and throughout Mexico and Central and South America. Island regions have an isolated breeding range that limits the ability of the species to disperse and colonize. Extensive land drainage practices in southern Texas have limited the range of the rice rat population in the United States. (Alvarez-Castaneda, 1994; Merriam, 1901; Vega, et al., 2007)

Habitat

Coues’ rice rats are mainly terrestrial mammals and generally inhabit swampy or marshy coastal edges with a shallower zone of aquatic grasses. They are adept swimmers and possess diving skills to use underwater habitats for escape routes, foraging, and hunting. Coues’ rice rats may also inhabit local high-mountain ranges. (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

Physical Description

Coues' rice rats are small rat-like rodents. They range from 242 to 265 mm in length, with an average mass of 42 to 83 g. They differ from well-studied marsh rice rats (Oryzomys palustris), because they are larger and less gray. Coues’ rice rats are covered with pelage of varying shades of brown on the upper parts, and lightly colored pelage on the limbs, face, and sides. Their backs have soft, dense, and water-repellant underfur. Males are slightly larger than females, but the difference is not statistically significant. The skull is light and thin with a maximum length of 30.5 mm, zygomatic breadth of 16 mm, interorbital breadth of 4.8 mm, and nasals are 11.9 mm apart. They are distinguishable from marsh rice rats as they have three rows of upper molar cusps as opposed to 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

Reproduction

Information about mating in Coues' rice rats in particular is limited, though their mating systems are likely similar to marsh rice rats. Male marsh rice rats have multiple mates, and females may as well. Associations between males and females are brief. (Dewsbury, 1970)

Scientists don't know much about how Coues' rice rats find mates, but the way they do is probably similar to their close relatives, marsh rice rats. Male marsh rice rats mate with more than one female, and females might also have more than one mate. Males and females don't spend time together except to mate. (Dewsbury, 1970)

Coues' rice rats are predicted to breed throughout the year based on availability of nesting locations. This suggests that breeding is heavily influenced by population and environmental variables. Females produce several litters of 2 to 7 young throughout their lifetime, with an average of 4 young per litter. The gestation period is 21 to 28 days. A single female is predicted to bear between 5 to 6 litters per year in optimal conditions, with many young produced during the months of January through May. The young become reproductively active around 7 weeks old. They are born naked and blind, weighing approximately 3 g each. Eyes are opened on the fifth or sixth day and they are weaned on the eleventh day. Both sexes reach sexual maturity after 40 to 45 days. However, juvenile rice rats do not reach their adult size of about 48 g until approximately 9 months after birth. (Benson and Gehlbach, 1979; Cook, et al., 2001; Vega, et al., 2007; Wolfe, 1982)

  • Breeding interval
    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
    4
  • 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 provide protection for altricial young in the form of nests from local vegetation in their habitat. Mothers are the primary source of food for young until they are weaned after about 11 days after birth. (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

Lifespan/Longevity

The maximum time recorded alive after capture of a Coues' rice rat was 599 days for both one male and one female. The predicted median time alive is 165 days for males and 167 days for females. (Clark, 1980)

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

Behavior

Similar to other rice rats, Coues' rice rats are highly active, nocturnal, and social. They build nests from local vegetation in their marshy habitat. Rice rats possess a predisposition for swimming and diving in both its natural habitat and during laboratory study. Their strong swimming skills are attributed to undulation of their tails in order to maintain a horizontal profile to readily enter the water for foraging or to escape predators. Rice rats frequently swim underwater for more than 10 meters at a time and engage in extensive self-grooming. Such behavior is predicted to be performed in order to maintain the water repellant quality of its pelage. (Cook, et al., 2001; Wolfe, 1982)

Home Range

There is no information available regarding the home range of Coues' rice rats. However, the average home range of the closely related species marsh rice rats (Oryzomys palustris) for males is 0.37 ha and for females the average home range is 0.23 ha. (Wolfe, 1982)

Communication and Perception

There is no information available regarding communication and perception in Coues' rice rats. Similar to other species of rice rats (Oryzomys), Coues' rice rats most likely rely on vision, hearing, taste, and smell in order to perceive and communicate in their environment. Laboratory studies suggest that the species relies heavily on olfaction and touch, based on sniffing and exploratory behavior when exposed to new environments. (Wolfe, 1982)

Food Habits

Coues' rice rats are omnivores. Information regarding their food habits varies throughout the literature. An early study observed that rice rats feed primarily on seeds and succulent plant parts, favor grass stems in meadow areas, and supplement their diet with meat consumption. A later study reported seasonal variation in the rice rat diet, in which ultimately equal amounts of plant and animal foods were eaten. Specific animal foods varied, but insects and snails were common in the diet. Fishes, deer mice, and sparrows are among the animal foods consumed by rice rats. Coues' rice rats store food in caches. (Goldman, 1918; Wolfe, 1982)

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

Predation

Rice rats are preyed upon by boa constrictors, who have a considerable impact on their populations in Central and South America. Rice rats are also an important food item in the diet of barn owls. Owls have been the best documented predators of the closely related species marsh rice rats (Oryzomys palustris). In general, rice rats are heavily preyed upon by hawks, owls, cottonmouths and water snakes. There is also evidence of predation by raccoons, red foxes, barred owls, minks, weasels, and skunks. (Vega, et al., 2007; Wolfe, 1982)

Ecosystem Roles

Coues' rice rats are prone to parasitic infection from species of mites and ticks , lice, fleas, digeneans, pentastomids, and coccidians. (Wolfe, 1982)

Commensal/Parasitic Species
  • mites and ticks (Acari)
  • lice (Phthiraptera)
  • fleas (Siphonaptera)
  • flatworms (Digenea)
  • tongue worms (Pentastomida)
  • internal parasites (Isospora)

Economic Importance for Humans: Positive

There are no known positive impacts of Coues' rice rats on humans. The two species have little interaction because the rats are most commonly found in swampy, marshy areas. (Goldman, 1918)

Economic Importance for Humans: Negative

Despite limited human contact, Coues' rice rats may perpetuate the spread of diseases. They are hosts to various ectoparasites such as mites and ticks, fleas, and lice, that could be transmitted to other animals or humans. Parasitological evidence from a marsh population in the United States shows that rice rats were infected by a species of flukes contracted by eating killifishes. Rice rats are known to have bacterial periodontal disease that is currently being researched in dentistry. (Wolfe, 1982)

Conservation Status

Coues' rice rats are classified as a species of least concern on the IUCN's Red List of Threatened Species. Coues' rice rats are most threatened by habitat loss from road construction. The main change that occurs from road construction is the increase in the proportion of edge that is exposed to a different habitat, leading to abiotic, direct biotic, and indirect biotic edge effects on the rodent population. (Fuentes-Montemayor, et al., 2009)

Contributors

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

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.

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