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Salt Marsh Harvest Mouse (Reithrodontomys raviventris raviventris) in the Redwood Shores Area* Perennial inhabitant of ereater San Francisco Bav tidal marshes. Federal endangered species: 35 Federal Register 16047 — 16048 (13 October 1970). California endangered species: Title 14, California Code of Regulations, § 670.5 (27 June 1971). Salt marsh harvest mice are members of the Cricetidae family, which includes field mice, lemmings, muskrats, hamsters, and gerbils (USFWS- Sacramento). There are two subspecies of salt marsh harvest mouse. The northern subspecies, Reithrodontomys raviventris haliocoetes, is found in Marin, Napa, Sonoma, Solano, and northern Contra Costa counties. The southern subspecies, R r. raviventris, occurs in San Mateo, Alameda, and Santa Clara counties, and in disjunct areas on the Marin peninsula. In the South Bay, populations of Rr. raviventris primarily occur south of a imaginary line across the Bay from Redwood City to Hayward. The two subspecies show some differences in chromosome shape, which may indicate that "genetic isolating mechanisms are beginning to form between them" (Shellhammer, 2000). This report addresses the southern subspecies, Rr. raviventris. Description Salt marsh harvest mice are among the smallest rodents in the U.S. Their bodies are 69 to 76 mm long (2.75 to 3 inches) and they weigh 8 to 12 grams (0.3 ounce), somewhat less than a nickel. The species name, Reithrodontomys raviventris, means groove- toothed mouse with a red belly (Shellhammer, 1998). Their backs are dark brown, their bellies and sides are pinkish - cinnamon to tawny (Cal /EPA DPR, on line). The mouse's tail can be bicolored and as long as or longer than the body. The Salt marsh harvest mouse is similar to the western harvest mouse, but has darker ears and dorsal areas; tails that are thicker, less pointed, and more uniform in color; and frequently darker bellies. R r. raviventris has a cinnamon orange or rufous color on the venter. Habitat. Salt marsh harvest mice require dense cover (USFNVS- Sacramento). Preferred habitat is tidal and diked coastal salt marshes characterized by dense growth of pickleweed (Salicornia vi�ginica). They are seldom found in cordgrass or alkali bulrush. Adjacent grasslands are also used by the mice, according to the Cal /EPA DPR, when new grass growth provides suitable cover. 10