By Dan Grannan
An adorable local watershed resident, the salt marsh harvest mouse, recently made national headlines when it became the center of a political controversy over the federal stimulus bill that included a thirty million dollar earmark for San Francisco Bay restoration. In fact, the mouse wasn’t in the stimulus bill at all, but the shaky status of this creature makes a strong case for the necessity of watershed restoration in the Bay Area.
The salt marsh harvest mouse is tiny. At approximately eight centimeters long, it weighs between eight to twelve grams. That length excludes the mouse’s tail, which can grow just as long as its body. The harvest mouse’s fur is brown along its back and grayish on its underside. Another variation has a reddish colored underside and is known as the red-bellied harvest mouse, a sub-species found only in the southern regions of the Bay Area.
Range and Habitat
The salt marsh harvest mouse is indigenous to the San Francisco Bay area, residing primarily in Suisun and San Pablo Bays, as well as the South Bay. Its habitat of choice is the deep, dense pickleweed found in coastal marsh areas, which provides necessary cover from avian predators. The mouse’s excellent swimming skills and ability to drink and eat very salty snacks demonstrate its successful adaptation to the environment. However, pickleweed is crucial to the mouse’s survival and the decline of this habitat has had major negative impacts on harvest mouse populations.
The salt marsh harvest mouse feasts on seeds, grasses, insects, and forbs (herbaceous, flowering plants). The tastiest treat of all for the mouse is pickleweed, which it eats like an ear of corn, holding the weed with its paws and chomping away with long, grooved teeth.
Mating and Life Span
Forever young, the mouse only lives about one year. Females have one litter, which consists of up to four little babies. Low reproductive rates coupled with a short life span make the species especially fragile.
While the salt water harvest mouse is susceptible to attacks from hawks, owls, herons and other predators, their number one enemy is development. The San Francisco Bay Area has lost approximately eighty-five percent of its marshland, largely to residential and commercial construction projects. Since being protected by the Endangered Species Act in 1973 the salt marsh harvest mouse has evaded extinction, but its remaining habitat is scattered and fragmented. Efforts to restore habitat are urgent. Habitat loss, continued development, and historic decline in the population have brought this species dangerously close to a critical designation on the Endangered Species List.