Family: Muridae, Mice and Rats view all from this family

Description Dark brown above; pinkish cinnamon or tawny below. Tail similarly bicolored. Upper incisors grooved. L 4 5/8-6 7/8” (118-175 mm); T 2 1/4-3 3/4” (56-96 mm); HF 5/8-7/8” (15-21 mm).

Endangered Status The Salt Marsh Harvest Mouse is on the U.S. Endangered Species List. It is classified as endangered in California, where it lives only in the San Francisco Bay area. This species lives in salt marsh habitat and was once found throughout the bay shoreline. Encroaching urbanization has left it with only about 20 percent of its historical range, and even parts of the remainder are under threat of development. The mouse and some of its habitat are protected in the San Francisco Bay National Wildlife Refuge, but even there it is in jeopardy. A nearby sewage treatment plant pumps millions of gallons of fresh water into the bay each day, and the resulting changes in salinity levels could change the shoreline vegetation and make the habitat unsuitable for the mouse.

Similar Species Western Harvest Mouse has a white belly.

Breeding Reproductive season March through October or November; litters of 4 young.

Habitat Salt marshes.

Range San Francisco Bay area of California.

Discussion The Salt-marsh Harvest Mouse is most active on moonlit nights. If cover is adequate, it will move into grasslands bordering the marshes. This mouse feeds mainly on seeds, including those of many grasses, and can drink seawater. It does not burrow. Owls, snakes, and many mammals prey upon it. The Salt-marsh Harvest Mouse does well in glasswort, succulent plants that recently have been increasing in number around San Francisco.