Rice Rat: Oryzomys palustris natator
Genus/Species: Oryzomys palustris
Subspecies: Orzomys palustris natator
Common Name: Rice rat (also known as the silver rice rat)
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
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).
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 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 .
Federal Recovery Plan
Other Informative Links
U.S. Fish & Wildlife Service Species Conservation Guidelines
U.S. Fish & Wildlife Service - Multi-Species Recovery Plan for South Florida
Printable version of this page
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 .
Wolfe, J.L. 1982. Oryzomys palustris. Mammalian Species 176:1-5.
Image Credit USFWS