Silver Rice Rat

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Silver Rice Rat

Oryzomys palustris natator

ListedApril 30, 1991
DescriptionSmall rodent with coarse fur and a long tail; back is silver-gray in color.
HabitatFreshwater marshes; flooded mangrove swamps; saltmarsh flats; elevated, seldom-flooded areas with abundant vegetation.
FoodSeeds, succulent parts of plants, insects, small crabs.
ReproductionProduces one to five young.
ThreatsChanging water levels, wetland clearance, development, predators, competition for food.


The silver rice rat is a small rodent, 10 in (25 cm) long, with coarse fur and a long tail of 5 in (13 cm). The species is named for and identified by the silver-gray color of its back. Taxonomic classification of the silver rice rat is a subject of debate. It is variously described as a separate species, Oryzomys argentatus, or as a geographic population of O. palustris natator.


It is a good swimmer and a nocturnal feeder, consuming seeds, the succulent parts of plants, insects, and small crabs over a range of 50 acres (20 hectares). Predators include foxes, skunks, snakes, birds of prey, and raccoons. Although little is known of breeding behavior in the wild, it is thought that one to five young are produced after a gestation of approximately 25 days.


In addition to freshwater marshes, this rat is known to inhabit flooded mangrove swamps, salt-marsh flats, andfor nestingelevated, seldom-flooded areas with abundant vegetation.


Although the silver rice rat occurs throughout Florida, it is the population in the lower Florida Keys in Monroe County that is endangered. Because of its nocturnal nature and resistance to trapping, no estimate of the population in the lower Florida Keys is available. The species occurs in low densities on Big Torch, Johnston, Middle Torch, Raccoon, Saddlebunch, Little Pine, Summerland, and Water Keys. A population occurring on Cudjoe Key is believed to have recently become extinct.


Distribution and population level of the silver rice rat was probably originally reduced with the changing water levels that resulted in the formation of the Florida Keys. The scattered and isolated populations are now vulnerable to increasing habitat reduction as a result of wetland clearance for commercial and residential development. Although the silver rice rat is preyed upon by a number of species, the raccoon is the most serious predator. Because of the availability of garbage as a food source on developed Keys, raccoonsnative to the areaare present in unnaturally high numbers. Also, the introduced Old World rat (Rattus rattus ) competes with the silver rice rat for space and food on several of the Keys.

Conservation and Recovery

Preservation of remaining habitat is the first step toward preserving the silver rice rat.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345


U.S. Fish and Wildlife Service. 30 April 1991. "Endangered and Threatened Wildlife and Plants: Endangered Status for the Lower Keys Populations of the Rice Rat (Silver Rice Rat)." Federal Register 56(83):19809-19814.