Rice Rat: Oryzomys palustris natator

Taxonomic Classification

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Genus/Species: Oryzomys palustris
Subspecies: Orzomys palustris natator
Common Name: Rice rat (also known as the silver rice rat)

Listing Status

Federal Status: Endangered
FL Status: Federally-designated Endangered (Lower Keys population)
FNAI Ranks: G5T2Q/S2 (Globally: Demonstrably Secure, Sub sp. Imperiled [subspecies classification questioned]/State: Imperiled)
IUCN Status: Not ranked

Physical Description

The rice rat (commonly called the silver rice rat) is a small rodent that can reach a length of 5.5 inches (14 centimeters).  The rice rat has a brownish-gray, gray, or brown back, with a gray belly and pale gray sides.  Rice rats also have a bi-colored tail that is white on bottom and brown on top (Humphrey 1992). 

Life History

Very little information is available about the life history of the rice rat, so information is summarized from a similar species, the marsh rice rat (Oryzomys palustris). 

Rice rats feed primarily insects, crabs, and snails, but they will also eat plants such as various species of marsh grasses.  This species is primarily nocturnal and occupies large home-ranges. (U.S. Fish and Wildlife Service 1999)

The rice rat can breed throughout the year.  Females carry the young for 21-28 days before giving birth.  The average litter size is around four or five and the juveniles weigh between 0.11 and 0.14 ounces (3.1-4 grams).  Females will begin weaning their young sometime between 11 and 20 days old.  Sexual maturity is reached between 50 to 60 days old (Wolfe 1982).  The lifespan of rice rats in the wild is usually less than a year.

Habitat and Distribution

Rice Rat Distribution MapRice rats inhabit salt marsh flats, mangrove swamps, and buttonwood transition vegetation in the Lower Florida Keys (U.S. Fish & Wildlife Service 1999).


Habitat loss is the main threat to the rice rat.  Development in marsh habitats by the process called “dredge and fill” has caused extensive damage to the population (U.S. Fish & Wildlife Service 1999).  Rice rats are vulnerable to low genetic variability due to its limited population.  As a species of the Florida Keys, rising sea level is a potential threat to the rice rat’s habitat because it would become inundated with water.

Conservation and Management

The Lower Keys population of the rice rat is protected as an Endangered species by the Federal Endangered Species Act and as a Federally-designated Endangered species by Florida’s Endangered and Threatened Species Rule External Website.

Federal Recovery Plan External Website

Other Informative Links

U.S. Fish & Wildlife Service Species Conservation Guidelines External Website
U.S. Fish & Wildlife Service - Multi-Species Recovery Plan for South Florida External Website



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Humphrey, S.R. 1992.  Lower Keys Population of Rice Rat Oryzomys palustris natator (in part).  Pages 300-309 in S.R. Humphrey (ed.), Rare and endangered biota of Florida.  Vol. I. Mammals.  University Press of Florida.  Gainesville, Florida.

U.S. Fish & Wildlife Service. (1999, May 18). Rice Rat. Retrieved August 5, 2011, from Multi Species Recovery Plan for South Florida: http://www.fws.gov/verobeach/MSRPPDFs/RiceRat.pdf External Website.

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

Image Credit USFWS

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