Research Article Salt Marsh Harvest Mouse Demography and Habitat Use in the Suisun Marsh, California DIEGO SUSTAITA, 1,2 California Department of Fish and Game, Bay Delta Region, 7329 Silverado Trail, Napa, CA 94558, USA PATTY FINFROCK QUICKERT, California Department of Water Resources, FloodSAFE Environmental Stewardship and Statewide Resources Office, 1416 Ninth Street Room 1623, Sacramento, CA 95814, USA LAURA PATTERSON, California Department of Water Resources, Division of Environmental Services, 3500 Industrial Boulevard, West Sacramento, CA 95691, USA LAUREEN BARTHMAN-THOMPSON, California Department of Fish and Game, Bay Delta Region, 7329 Silverado Trail, Napa, CA 94558, USA SARAH ESTRELLA, California Department of Fish and Game, Bay Delta Region, 7329 Silverado Trail, Napa, CA 94558, USA ABSTRACT We undertook a 2-year (2002–2004) mark–recapture study to investigate demographic performance and habitat use of salt marsh harvest mice (Reithrodontomys raviventris halicoetes) in the Suisun Marsh. We examined the effects of different wetland types and microhabitats on 3 demographic variables: density, reproductive potential, and persistence. Our results indicate that microhabitats dominated by mixed vegetation or pickleweed (Salicornia spp.) supported similar salt marsh harvest mouse densities, reproductive potential, and persistence throughout much of the year, whereas few salt marsh harvest mice inhabited upland grass-dominated microhabitats. We found that densities were higher in diked wetlands, whereas post-winter persistence was higher in tidal wetlands, and reproductive potential did not differ statistically between wetland types. Our results emphasize the importance of mixed vegetation for providing adequate salt marsh harvest mouse habitat and suggest that, despite their physiognomic and hydrological differences, both diked and tidal wetlands support salt marsh harvest mouse populations by promoting different demographic attributes. We recommend that habitat management, restoration, and enhancement efforts include areas containing mixed vegetation in addition to pickleweed in both diked and tidal wetlands. ß 2011 The Wildlife Society. KEY WORDS density, diked, microhabitat, persistence, Reithrodontomys raviventris halicoetes, reproduction, salt marsh harvest mouse, Suisun Marsh, tidal, wetlands. The salt marsh harvest mouse (Reithrodontomys raviventris) is endemic to the marshes of the San Francisco Bay Estuary in northern California. There are 2 subspecies: the southern (R. r. raviventris), which occurs in salt marshes around San Francisco Bay, and the northern (R. r. halicoetes), which occurs in brackish marshes around Suisun Bay and San Pablo Bay (Fisler 1965, Shellhammer 1982). The species’ historical tidal marsh habitat has decreased by approximately 80% due to diking, draining, and filling for urban, industrial, and agricultural development (Goals Project 1999), leading to its listing as endangered by both the federal and state governments (Federal Register 50 CFR 17.11; U.S. Fish and Wildlife Service [USFWS] 1973; California Code of Regulations Title 14, Section 670.5[a][6][F]). Most pub- lished research on salt marsh harvest mouse ecology was conducted in salt marshes around the South San Francisco Bay. Based on those studies, optimal salt marsh harvest mouse habitat has commonly been described as tidal marsh dominated by pickleweed (Salicornia spp.; Shellhammer et al. 1982, Shellhammer 1989, USFWS 2009). However, eco- logical conditions vary considerably across the range of the species, so the attributes of preferred habitat in one geo- graphic area may not apply universally (Fisler 1965, Shellhammer 1982, Goals Project 1999). Marshes in the San Francisco Bay have generally been more heavily impact- ed by development. Remaining salt marsh harvest mouse habitat in this area occurs as narrow bands of high tidal marsh with low-growing pickleweed and Pacific cordgrass (Spartina foliosa; Goals Project 1999) and little or no high marsh transition zone or bordering uplands to serve as refugia during high tides (Shellhammer 1977, Duke and Shellhammer 2006). In contrast to those in the San Francisco Bay, marshes in and around Suisun and San Pablo bays are generally larger in area and have significant transition zones and adjacent uplands. Tidal marshes in San Pablo Bay are vegetated primarily with pickleweed, whereas Suisun Marsh is more botanically diverse than other parts of the estuary (Goals Project 1999). Received: 12 February 2010; Accepted: 22 December 2010; Published: 18 July 2011 Additional Supporting Information may be found in the online version of this article. 1 E-mail: diego.sustaita@uconn.edu 2 Present Address: Department of Ecology and Evolutionary Biology, University of Connecticut, 75 North Eagleville Road, Unit 3043, Storrs, CT 06269-3043, USA. The Journal of Wildlife Management 75(6):1498–1507; 2011; DOI: 10.1002/jwmg.187 1498 The Journal of Wildlife Management  75(6)