U.S. Fish & Wildlife Service

Sacramento Fish & Wildlife OfficeServing the people, conserving the fish, wildlife, and plants of California

A Unit Of The Pacific Southwest Region

Kids' Species Information


Salt Marsh Harvest Mouse


Endangered. This means that the species is in danger of dying out. We are working hard to prevent this.

Salt marsh harvest mouse

Photo: Howard Shellhammer


The salt marsh harvest mouse is a small rodent.

It is about 69-75 mm long (2.75-3.0 inches). It weighs 9-14 g (0.3-0.5 ounces). The tail can be as long or longer than the body.

There are two subspecies: northern and southern. The northern ones in the marshes of the San Pablo and Suisun bays. The southern ones in the marshes of Corte Madera, Richmond and South San Francisco Bay.


Leaves, seeds and stems of plants. In winter, the mice seem to prefer fresh green grasses. The rest of the year, they prefer pickleweed and saltgrass.

The northern subspecies can drink sea water but prefers fresh water. The southern subspecies can't live completely on sea water but it prefers moderately salty water over fresh.


Dense pickleweed. Mice also move into adjoining grasslands during the highest winter tides.


Breeding goes on from spring through autumn. But each female usually has only one or two litters per year. Average litter size is about four. Nests are quite minimal, often built over old birds' nests. Members of the southern group often don't make a nest at all.


Hawks, snakes and owls. Shorebirds and larger mammals. House cats.


Most of the marshes that used to be around the San Francisco Bay are gone. Lots of the remaining marsh is not good for the mice.


Salt Marsh Harvest Mouse (91 KB PDF) from the California Dept. of Pesticide Regulation. This publication is designed to help farmers avoid salt marsh harvest mice. But it has lots of pictures and information.

Thelander, C. ed. 1994. Life on the edge: a guide to California's endangered natural resources. BioSystem Books. Santa Cruz, CA. p 80-81.

A marsh is a marsh is a marsh . . . but not always to a salt marsh harvest mouse. Tidelines, Don Edwards San Francisco Bay National Wildlife Refuge.

Salt Marsh Harvest Mouse (533 KB PDF) from the Invasive Spartina Project. We provide some of the funding for this project.

Photo Credit: Howard Shellhammer

Words to Learn

Biologists call salt marsh harvest mice Reithrodontomys raviventris. Scientific names are in Latin or Greek. The name means "groove toothed mouse with a red belly."

They are in the Cricetidae family, which includes field mice, lemmings, muskrats, hamsters and gerbils.

The northern subspecies (ssp.) is called Reithrodontomys raviventris halicoetes.

The southern ssp. is called Reithrodontomys raviventris raviventris.

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Last updated: November 29, 2017