Salt Marsh Harvest Mouse
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The salt marsh harvest mouse is among
the smallest rodents in the U.S.
(Paul Kelly/EPA)
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The salt marsh harvest mouse is a tiny, nocturnal rodent that lives in San Francisco Bay wetlands. The mouse can only be found along the Bay. It was listed as an endangered species in 1970.
Salt marsh harvest mice are among the smallest rodents in the United States. Their brown bodies are less than three inches long, which is about the size of a thumb, and weigh less than a nickel. Their tails can be as long or longer than their bodies, and they have grooved teeth.
Salt marsh harvest mice eat seeds, grasses, pickleweed and insects, and are active mostly at night. Unlike most mammals, their bodies are specially adapted to tolerate high concentrations of salt in food and water. The mice have been known to drink and survive on salt water or brackish water for long periods of time, which has given them a great advantage in the Bay’s salty tidal marshes where only a limited number of creatures can survive.
Because of their small size, salt marsh harvest mice live in areas of dense pickleweed, which provides ample hiding places from natural predators, such as hawks, owls, herons, and clapper rails. During very high tides, water covers the pickleweed, and the mice must either swim or climb onto plants that grow above the high tide line. For this reason, salt marsh harvest mice are very good swimmers and climbers, but they also depend on the bushy vegetation that rings Bay wetlands.
Salt marsh harvest mice live very short lives—most live less than 8 months, but they can live as long as one year. Unlike most rodents, they do not reproduce quickly: females bear only about four young per litter, and have only one litter in their lifetime.
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