Salt Marsh Harvest Mouse

The Salt Marsh Harvest Mouse (Reithrodontomys raviventris), also known as the Red-bellied Harvest Mouse, is an endangered rodent endemic to the San Francisco Bay Area salt marshes in California.^[1] There are two distinct subspecies, both endangered and listed together on federal and state endangered species lists. The northern subspecies (Reithrodontomys raviventris halicoetes) is lighter in color and inhabits the northern marshes of the bay, and the southern subspecies (Reithrodontomys raviventris raviventris) lives in the East and South Bay marshes. They are both quite similar in appearance to their parent species, the Western harvest mouse. Its endangered designation is due to its limited range, historic decline in population and continuing threat of habitat loss due to development encroachment at the perimeter of San Francisco Bay.

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Description and comparison to similar species

The Salt Marsh Harvest Mouse has dark brown fur above and a pinkish cinnamon or tawny belly; moreover, the tail is likewise bicolored. An adult's length is twelve to eighteen centimeters and a tail length of six to ten centimeters. The height is between 1.5 and 2.1 centimeters. Weight of a mature mouse is approximately 10 to 20 grams. The upper incisors are grooved.

This species is nocturnal, with particularly noted activity on moonlit nights. This mouse is particularly resourceful, making use of ground runways of other rodents; moreover, he also exhibits climbing agility. It enjoys subsisting in marsh habitats where glasswort abounds. Luckily the glasswort plant has been increasing around the San Francisco Bay perimeter since the 1980s. Its many predators feature hawk, snake and owl species, as well as shorebirds and larger mammals. Predation by domestic cats is an issue due to encroachment of the limited habitat by humans at the perimeter of the San Francisco Bay.

As would be expected of a mouse native to salt marshes, this species is a competent swimmer and is tolerant of salt in its diet and water supply. It can drink salt water and sometimes even prefers it to fresh. It eats seeds and plants, especially pickleweed and glasswort, one of the most common salt marsh plant species.

Similar species are the Plains harvest mouse, which has a distinct but narrower stripe on its spine, and the Fulvous harvest mouse, which has a longer tail. Also similar is the Western harvest mouse, which has an underbelly fur that is whitish in color and an indistinct white stripe along the fur above its spine. Finally the House mouse has incisors without grooves, unlike those of the Salt Marsh Harvest Mouse.

Range

This organism is known to be found in the following specific locales (among others):

• Sonoma Creek discharge area known as the Napa Sonoma Marsh
• Sausalito baylands
• San Rafael baylands
• San Francisco Bay sloughs in Alviso

Conservation

The Salt Marsh Harvest Mouse has been forced out of much of its habitat by extensive development of bayside marshland. Pollution, boat activity, commercial salt harvesting; moreover, decrease in native plant material has also reduced the species' numbers. It has been on the endangered lists since the 1970s, and has protected habitat within numerous Bay Area wildlife refuges. Individual political jurisdictions have conducted research and established habitat protection strategies to protect the Salt Marsh Harvest Mouse. For example, the city of San Rafael, California has established a shoreline setback standard to prevent any land development within fifty feet of the shoreline; this measure has been applied to several specific land developments along the San Francisco Bay shoreline.^[2]

Line note references

Bibliography

• National Audubon Society Field Guide to North American Mammals, ed. by John O. Whitaker Jr., Chanticleer Press (1997) ISBN 0-679-44631-1
• Shellhammer (2000). Reithrodontomys raviventris. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes a brief justification of why this species is vulnerable and the criteria used