Marsh oryzomys, Rice meadow-mouse, Rice-field mouse, Rice rat, Marsh mouse, Swamp rice rat
The marsh rice rat (Oryzomys palustris ) is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, from New Jersey and Kansas south to Florida and northeasternmost Tamaulipas, Mexico; its range previously extended further west and north, where it may have been a commensal in corn-cultivating communities. Weighing about 40 to 80 g (1.4 to 2.8 oz), the marsh rice rat is a medium-sized rodent that resembles the common black and brown rat. The upperparts are generally gray-brown, but are reddish in many Florida populations. The feet show several specializations for life in the water. The skull is large and flattened, and is short at the front.
John Bachman discovered the marsh rice rat in 1816, and it was formally described in 1837. Several subspecies have been described since the 1890s, mainly from Florida, but disagreement exists over their validity. The Florida Keys population is sometimes classified as a different species, the silver rice rat (Oryzomys argentatus ). Data from the mitochondrial cytochrome b gene indicate a deep divergence between populations east of Mississippi and those further west, which suggests that the western populations may be recognized as a separate species, Oryzomys texensis. The species is part of the genus Oryzomys, which also includes several others occurring further south in Mexico, Central America, and northwestern South America, some of which have previously been regarded as subspecies of the marsh rice rat. One, Oryzomys couesi, occurs with the marsh rice rat in Tamaulipas and southern Texas.
The marsh rice rat is active during the night, makes nests of sedge and grass, and occasionally builds runways. Its diverse diet includes plants, fungi, and a variety of animals. Population densities are usually below 10 per ha (four per acre) and home ranges vary from 0.23 to 0.37 ha (0.57 to 0.91 acres), depending on sex and geography. Litters of generally three to five young are born after a pregnancy around 25 days, mainly during the summer. Newborns are helpless at birth, but are weaned after a few weeks. Several animals prey on the marsh rice rat, including the barn owl, and it usually lives for less than a year in the wild. It is infected by many different parasites and harbors a hantavirus that also infects humans. The species is not of conservation concern, but some populations are threatened.
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NocturnalNocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal",...
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HerbivoreA herbivore is an animal anatomically and physiologically adapted to eating plant material, for example, foliage, for the main component of its die...
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GranivoreSeed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of pla...
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GraminivoreIn zoology, a graminivore (not to be confused with a granivore) is an herbivorous animal that feeds primarily on grass. Graminivory is a form of g...
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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ScavengerScavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While sc...
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SemiaquaticSemiaquatic animals are those that are primarily or partly terrestrial but that spend a large amount of time swimming or otherwise occupied in wate...
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PredatorPredators are animals that kill and eat other organisms, their prey. Predators may actively search for or pursue prey or wait for it, often conceal...
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AltricialAltricial animals are those species whose newly hatched or born young are relatively immobile. They lack hair or down, are not able to obtain food ...
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BurrowingA burrow is a hole or tunnel excavated into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct ...
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
Among animals, viviparity is the development of the embryo inside the body of the parent. The term 'viviparity' and its adjective form 'viviparous'...
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SolitaryNo
Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withThe Marsh rice rat is a medium-sized semiaquatic North American rodent that resembles the Common black and Brown rat. Its upper parts are generally gray-brown but are reddish in many Florida populations. The feet show several specializations for life in the water. It has small cheek pouches. The ears are about the same color as the upper parts, but a patch of light hairs is in front of them. The tail is dark brown above and may be paler below. The guard hairs are long and have unpigmented, silvery tips. When rice rats swim, the air is trapped in their fur, which increases buoyancy and reduces heat loss.
Marsh rice rats occur in much of the eastern and southern United States, northeast to southern New Jersey, and south to southeastern Texas and far northeastern Tamaulipas, Mexico. They live in several habitats, ranging from coastal salt marshes to mountain streams and clearings. They prefer areas where the ground is covered with grasses and sedges, which protect them from predators. Marsh rice rats also occur in drier uplands, which serve as sinks for young, dispersing animals and as refuges during high tide.
Marsh rice rats are semiaquatic, spending much of their time in the water. They are active during the night, so are rarely seen. They build nests of sedge and grass, about 13 cm (5 in) large, which are placed under debris, near shrubs, in short burrows, or high in aquatic vegetation. They may also use old nests of marsh wrens, red-winged blackbirds, and muskrats. Marsh rice rats sometimes make large runways or dig burrows. They are excellent swimmers, easily swimming more than 10 m (33 ft) under water, and often seek safety in the water when alarmed. They may occasionally climb in vegetation, but never higher than 90 cm (3.0 ft). Marsh rice rats are very clean and extensively groom themselves, perhaps to keep their fur water-repellent. They are solitary and territorial creatures that are aggressive towards conspecifics and emit high-pitched squeaks while fighting.
Marsh rice rats are carnivores, herbivores, and scavengers. They take both vegetable and animal food. They eat mainly seeds and succulent parts of plants. Animal food includes insects, fiddler crabs, snails, fish, clams, and juvenile turtles. They scavenge on carcasses of muskrats, deermice, and sparrows, and may be the most important predator on eggs and young of the marsh wren. Rice rats also eat eggs and chicks of ground-nesting birds and may even prey on alligator eggs.
Marsh rice rats breed mostly during the summer. After a gestation of about 25 days, females give birth to 3-5 young, although litter sizes may vary from 1 to 7. Females may have up to 6 litters a year. Newborns weigh 3 to 4 g (about 0.10 to 0.15 oz) and are blind and almost naked. The external ears (pinnae) soon unfold and on the first day, claws are visible and the young emit high-pitched squeaks. On the second day, they are able to crawl, and during the third to fifth days, the whiskers and eyelids develop. Between the 8th and 11th days, their eyes open, the fur develops, and the young begin to take solid food. Weaning occurs on the 11th to 20th day, and reproductive maturity is reached at about 50 to 60 days old.
The Marsh rice rat is a common, widespread, and stable species without major threats. However, the Florida Keys form is rare and in decline and is threatened by competition with the black rat, predation by domestic cats, habitat loss, and loss of genetic variation; in this area, the species is considered endangered. Changes in climate may also reduce the range of the Marsh rice rat in Texas, where it is now common, but may become threatened by habitat loss in the future.
The IUCN Red List and other sources don’t provide the number of the Marsh rice rat total population size. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
