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A University of Vermont Faxonomia report (Vermont 1996) describes preferred habitat for the mouse as having the following characteristics: ■ Areas having 100 percent cover. ■ Depth of vegetation at summer maximum of 30 — 50 cm. • Vegetation composed of 100 percent pickleweed to 50 percent pickleweed with other halophytes, particularly fat hen (Atriplex patula) and alkali heath (Franklin grand folia). • Few to no areas of salt grass (Disticlis.rpicata), brass buttons (Cotula comn opifolia), alkali bulrush, other Scirpus species or T_ypba. ■ Large marsh areas. ■ No openground or water bifurcating the vegetation. ■ Minimal disruption. In marshes where there is an adjacent zone of salt - tolerant plants, the mice will use this zone to escape form higher tides, and "may even spend a considerable portion of their lives there," as well as in adjoining grasslands (USFWS- Sacramento). Migration and Home Ranges. There is some movement from pickleweed marsh to higher grasslands in the spring and summer, or when plant cover provides escape from predators. This behavior appears to occur daily, rather than as shifts in habitat (CDFG on line). According to Shellhammer (1977 in CDFG online), individual mice do not move between marshes. However, Bias and Morrison (1999) found that the mice readily cross barren dikes, roads, and tidal channels greater than 2 meters wide (Bias, 2001). Similarly, Geissel et al. 1988) observed that barren areas do not serve as effective barriers to movements between populations of the mice (Bias 2001). Bias and Morrison found that the greatest distances traveled by the mice occur in June (Bias 2001). Geissel reported home ranges of the mice to be approximately 1,550 m'' -in males and about 1,300 m- in females (cited in Bias 2001); Bias and Morrison found ranges approximately 150 percent larger (cited in Bias 2001), although different techniques were employed in the two studies. Both Geissel and Bias and Morrison reported that males move farther than females (caducks.org). In narrow elongated marshes, ranges appear to be smaller; in one marsh north of Alviso, Rice (n.d., cited in fwie.fw.vt.edu) observed home ranges varying from 20 to 300 meters long by 5 meters wide, i.e., 100 m- to 1,500 m-, with most ranges in the 100 to 150 m'- range. Feeding. Salt marsh harvest mice are presumed to feed on seeds, grasses, and forb. Pickleweed and salt grass are the most common foods, with fresh green grasses the food of choice in the winter (Cal /EPA DPR online). They have longer intestines than the western harvest mouse (USFWS- Sacramento), indicative of a primarily herbivorous diet (CDFG on line). They are capable of drinking salt water, as well as brackish and freshwater (Cal /EPA DPR online). Although the northern subspecies can drink pure seawater, the southern subspecies cannot subsist solely on sea water; however, R. r. raviventris prefers moderately salty water over fresh (USFWS- Sacramento). Reproduction. The mice breed from spring to fall, having one to two litters per year (Cal /EPA DPR online). The breeding season for R. r. raviventris begins in March. An average female will have one litter of three to four young, although some may have two litters (Shellhammer, 1998). Fisler (1995), cited in LSA (2004), indicates that the southern subspecies may have two litters per year, but that the shorter (May forward) breeding season in the northern subspecies typically limits breeding to one litter per season. 11