the ear often form an ochraceous tuft. Hind feet 

 and tail are usually very dark. The tip of the tail is 

 blunt as opposed to pointed in R. megalotis, and 

 the thickness of the tail is greater (2.1 mm) 20 

 mm distal from the base (Fisler 1965:14). The 

 skull is longer than in R. megalotis (Dixon 1908, 

 1909; Howell 1914; Hall and Kelson 1959). 



RANGE 



R. raviventris is restricted to salt and brackish 

 marshes bordering south San Francisco, San 

 Pablo, and Suisun Bays. It is found on both sides 

 of the Golden Gate and the Sacramento River. 

 Two subspecies have been described, which differ 

 in some aspects of morphology, coloration, and 

 behavior (Fisler 1965). The easternmost occur- 

 rence of the species is in the vicinity of Antioch, 

 eastern Contra Costa County, and the extreme 

 western occurrence is in Sacramento County. A 

 marginal record from Grand Island, 2 miles north 

 of Knight's Landing, Solano County (Hall and 

 Kelson 1959) is actually a capture of/?, megalotis 

 (Fisler 1965). 



RANGE MAP 



Distribution is shown on the accompanying 

 map (Fisler 1965, Shellhammer, 1977). To make 

 the locations of populations visible on the map, 

 the width of the coastal strip occupied by the 

 mice has been exaggerated. Often the distribution 

 is limited to a linear strip of marsh within a few 

 hundred feet of the coast. 



STATES/COUNTIES 



California 



HABITAT 



Sonoma, Solano, Marin, Contra 

 Costa, San Mateo, Alameda, Santa 

 Clara, Sacramento, Napa. 



This mouse is restricted to salt and brackish 

 marshes where plants provide a dense mat of 

 cover, ideally 0.2 to 1.0 m high, and a network of 

 spaces on the ground (Hooper 1944, Wondolleck 

 et al. 1976). Pickleweed {Salicornia) is the most 

 important indicator species; other plants typical 

 of R. raviventris habitat are Atriplex semibaccata, 

 A. patula, Grindelia cunifolia, Spartina, and 

 Distichlis. 



FOOD AND FORAGING BEHAVIOR 



The salt marsh harvest mouse's diet is domi- 

 nated by green vegetation. It can eat salt grass 

 (Distichlis) and pickleweed (Salicornia), as well 

 as some seeds. Seasonal shifts in diet are influ- 

 enced by available food plants: much more green 

 vegetation is eaten in winter (Fisler 1965). 



SHELTER REQUIREMENTS 



It is restricted to areas with considerable 

 cover, mostly in the form of halophytic vegeta- 

 tion, and does not venture into open areas, even a 

 few feet from vegetation (Fisler 1965, Zetterquist 

 1977). Since most of its habitat is within the 

 range of the extreme high winter tides, high 

 ground from which to escape the rising water is a 

 necessity. The lower high tides of summer are 

 avoided by climbing into the higher vegetation of 

 the marsh or by swimming to floating objects 

 (Fisler 1965). Fills and habitat alteration along 

 the upper edge of marshes that have no cover are 

 unsuitable as refugia. 



NESTING OR BEDDING 



The subspecies R. r. halicoetes builds a nest of 

 dry grasses or sedges, usually located on the 

 ground or in a hummock of vegetation. Nests are 

 often used by several individuals, and are aban- 

 doned when fouled (Fisler 1965). Reithrodonto- 

 mys r. raviventris is not known to build nests, but 

 merely huddles in an accumulation of vegetation 

 or nesting material (Fisler 1965). It is also reported 

 to use abandoned nests of other species as tempo- 

 rary shelters, including those of song sparrows 

 Qohnston 1956). 



RITUAL REQUIREMENTS 



Not known. Its secretive habits render field 

 observation difficult. 



OTHER CRITICAL ENVIRONMENTAL 

 REQUIREMNTS 



Fisler (1965) stressed the behavioral adapta- 

 tions in R. raviventris that restrict it to areas of 

 high cover: a placid temperament and loss of the 

 frenetic escape behavior typical of R. megalotis. 

 R. raviventris is strongly dependent on the 

 presence of densely vegetated salt marsh habitat 

 for survival. 



