R. raviventris can be distinguished from R. megalotis by its slender, more pointed and more unicolored tail. R. raviventris was once divided into two different species, but is now considered a single species with two subspecies: R. ravivnetris halicoetes and R. r. raviventris.
Communication in this species has not been documented. However, like most mice, their communication probably involves some combination of visual, accoustic, olfactory, and tactile cues.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
Main reasons for the low population of salt marsh harvest mice is damage of wetlands, habitat destruction, and vegetation changes. Groundwater pumping has been diminishing marsh size in particular areas, while sewage dumping has contaminated others. Much of the marsh land habitat historically used by this species has been diked or drained, and almost all marshes around the San Francisco Bay area are too small and too far apart to support large populations. The extent of habitat fragmentation makes it difficult for this species to breed and recolonize habitat.
In 1972, The San Francisco Bay National Wildlife Refuge was founded, and has protected marshes in the South Bay. The largest of these marshes is Greco Island. California has obtained several areas that supply mouse habitat: Grizzly Island and Joyce Island Wildlife Areas, Hill Slough Wildlife Area, and Peytonia Slough Ecological Reserve. Also, another recovery plan was established in 1984. This plan has aimed to conserve the salt marsh harvest mouse through acquisition of larger marsh areas to combine with existing small isolated ones; altering upper edges of most marshes to provide three species of plants as refuges for mice when they get stressed by flooding.
US Federal List: endangered
CITES: no special status
IUCN Red List of Threatened Species: endangered
R. raviventris is listed as an endangered species by the US Fish and Wildlife service. In order to protect this species, certain measures must be taken to protect its salt marsh habitat. This sort of protection probably interferes to some extent in human plans to develop, drain, dike, dam, and otherwise modify the salt marshes surrounding San Franscisco Bay. Although preservation of this habitat may not be considered a negative thing by most people, it probably affects some sections of the human economy negatively.
These mice have little or no positive impact on people. However, they serve as food for animals which humans enjoy watching, such as hawks, owls, egrets, and foxes, so they can be considered to have an indirect positive entertainment value.
These mice do not have high population densities or high rates of reproduction, so it is not likley that they are an important food source for any one species. It is unknown if they play a role in dispersal of seeds.
The diet of salt marsh harvest mice seems to consist mainly of salt marsh plants, such as pickle weed. These mice eat a low ration of seeds and insects also. In winter, the diet switches mainly to grasses. In a unique adaptation to its habitat, this species is apparently tolerant of drinking saline water.
Animal Foods: insects
Plant Foods: leaves; seeds, grains, and nuts
Primary Diet: herbivore (Folivore , Granivore , Lignivore)
Salt-marsh harvest mice (Reithrodontomys raviventris), are limited to saltwater and brackish marshes bordering the San Francisco Bay area. Because these marshes have been altered by humans, throught draining, diking, and similar opperations, the distribution of this species is disjunct. The large Petaluma Marsh (in Sonoma County) supports a considerable amount of salt marsh harvest mice. The species is distributed eastward through Suisun Bay to the opening of the Sacramento River at Antioch Dunies. It reaches western regions through the marshes at the opening of Callinas Creek on the upper Marin Peninsula, and as far south to the San Mateo Bridge; including marshes in the San Francisco Bay National Wildlife Refuge.
Biogeographic Regions: nearctic (Native )
Salt-marsh harvest mice inhabit saline or brackish marshes. This species requires dense ground cover. R. raviventris prefers the cover of pickle weed, provided that it has non--submerged, salt-tolerant vegetation for escape during high tides. These mice rarely venture into the open.
Habitat Regions: temperate ; terrestrial
Wetlands: marsh
Most live less than 1 year. The longest it has been seen to live in the wild is about 18 months.
Range lifespan
Status: wild: 18 (high) months.
Typical lifespan
Status: wild: 12 (high) months.
R. raviventris has a dark brown dorsal area with a dark stripe extending vertically on its back, and pinkish cinnamon or tawny on its ventral side. There are often tufts of yellowish hairs near the anterior base of the ears. The ears themselves are dark in color. The tail is indistingly bicolored, with brownish hairs on the surface. Salt marsh harvest mice from the Southern San Francisco Bay area usually have a red belly. Toward the north, many members of the species have a white belly.
R. raviventris has a total length ranging from 118 to 175 mm. Tail length is reported at between 56 and 95 mm. The hindfoot length is 15 to 21 mm. These animals can weight between 7.6 and 14.5 g.
Range mass: 7.6 to 14.5 g.
Average mass: 11.01 g.
Range length: 118 to 175 mm.
Other Physical Features: endothermic ; bilateral symmetry
Members of the genus Reithrodontomys are eaten by many predaotrs, inclduing such as hawks, egrets, snakes, and skunks, but also by introduced rats, cats, and red foxes.
The mating system of salt marsh harvest mice has not been described. However, a congeneric mouse species, R. megalotis is reported to be polygynous.
Females have a long breeding season that is from March to October or November, but reproductive prospective is low. Males are reproductively active from April to September. The average litter is approximately 4. Usually a female produces only one litter per year, although they are capable of bearing two to three litters per year. This makes these mice quite different from their congener, R. megalotis, which can produce litters just about every month, provided the weather is not too cold.
Gestation periods of the genus Reithrodontomys are 21-24 days.
Occurrance of maturation events, such as eruption of incisors, opening of ear pinnae and eyes, weaning and dispersal are not reported for R. raviventris. However, in R. megalotis, these events are well documented. In this latter species, neonates weigh between 1 and 1.5 g. They are born naked and helpless. They are only 7 to 8 mm in length. They grow hair and begin to crawl by the age of 5 days, and their manidublar incisors begin to emerge through the gums byt his time also. By day 11 or 12, the eyes and ears open. Baby R. megalotis are completely weaned by about 24 days of age, and disperse shortly thereafter.
The timing of such events in R. megalotis may, or may not, be suggestive of the timing of such events in R. raviventris. Because salt marsh harvest mice are quite different from their congeners in their rate of reproduction, they may also be different in timing of developmental events.
Breeding interval: These mice typically breed once annually.
Breeding season: Breeding occurs from March to October or November.
Range number of offspring: 4 (high) .
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Reports of parental care in this species are not available. However, young of this genus are altricial, and require care from adults. In all mammals, females care for their young, providing them with milk, with shelter, and with protection until they reach the age of independence. It is not known if males of R. raviventris contribute to parental care.
Parental Investment: no parental involvement; altricial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
