Salt marsh harvest mouse
|Salt marsh harvest mouse|
The salt marsh harvest mouse (Reithrodontomys raviventris), also known as the red-bellied harvest mouse and sometimes called the saltmarsh harvest mouse, is an endangered rodent endemic to the San Francisco Bay Area salt marshes in California. 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.
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 (5 to 7 inches) and a tail length of six to ten centimeters (2 to 4 inches). The height is between 1.5 and 2.1 centimeters (0.6 to 0.8 inches). Weight of a mature mouse is approximately 10 to 20 grams (0.35 to 0.7 ounces). 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 for extended periods of time if necessary, 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.
The salt marsh harvest mouse has an average maximum age of 12 months, however most of the mice only live to about eight months. They do not have a high reproductive cycle as other species of mice would. They usually have around 4 offspring per litter and usually only once a year. They are a density- dependent species meaning when populations begin to rise the breeding time is pushed back into later spring. However if population density is too high, the populations can face the reality of extinction. Summer, when salinity of water and vegetation increases the mice have a notable advantage due to their ability to drink and survive purely on salt water. The northern species can survive purely on salt water, however prefers fresh to salt. Souther species can survive on either and does not display a preference to either.
The mice are dependent heavily on vegetation cover. Thus they can only survive under thick vegetation. Specifically they are dependent on thick cover of plants that thrive in salt water. They include salt marsh herbs, grasses and reeds. The pickleweed (Salicornia virginica) is their primary and preferred habitat as well their main food source. The salt marsh Harvest mouse is not an aggressive species thus enabling many mice to live in close quarters which gives them the ability to withstand short durations of high population density. Salinity is also a key factor in their habitat, low salinity Marshlands and less pickleweeds do not provide much of a habitat for the species. This is a major key to their habitat loss and species endangerment. Their diet also consists of seeds, grasses and some insects. They can also survive tidal or seasonal flooding due to their superior ability to swim, float and climb.
This organism is known to be found in the following specific locales (among others):
- Sonoma Creek discharge area known as the Napa Sonoma Marsh
- Alman Marsh, adjacent to Shollenberger Park, Petaluma
- Sausalito baylands
- San Rafael baylands
- San Francisco Bay sloughs in Alviso
- Palo Alto baylands
- Bair Island
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.
Reference in 2009 economic stimulus debate
The preservation of the salt marsh harvest mouse habitat was a subject of discussion in 2009 Economic Stimulus package. The mouse was mentioned numerous times in congress by Republicans such as Rep. Mike Pence and Rep. Dan Lungren to highlight the wasteful spending of the bill. It was claimed that $30m of the 2009 economic stimulus would be spent on habitat restoration to protect the mouse. The rumor was apparently started by Michael Steel, press secretary for John Boehner. This was disputed in a San Francisco Chronicle article by Democratic U.S. Rep Jackie Speier.
- Whitaker Jr., J.O., Hammerson, G. & Williams, D.F. (2008). "Reithrodontomys raviventris". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved 5 February 2010.
- Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. Mammal Species of the World a Taxonomic and Geographic Reference, D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore
- Golovanova, Galina. The Biogeography of the Salt Marsh Harvest Mouse (Reithrodonomys raviventris).
- Hogan, C. Michael et al. (1989). Spinnaker-on-the-Bay Expanded Initial Study, Earth Metrics Inc., prepared for the city of San Rafael, California
- Mentions of the Mouse. Metavid.org (2009-02-13). Retrieved on 2012-12-30.
- Mercury News: Bay Area mouse spurs national debate over stimulus bill. February 13, 2009.
- Erbe, Bonnie. Republicans Flop On Pelosi Mouse Lie, Haven't Learned Environmental Lesson. CBS News. 13 February 2009.
- Speier, Jackie (14 February 2009). The myth of the 'San Francisco mouse'. sfgate.com
- 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. www.iucnredlist.org. Retrieved on 11 May 2006. Database entry includes a brief justification of why this species is vulnerable and the criteria used