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. .� � Behavior. Clapper rails are considered to be non-migratory, although post-breeding dispersal in the fall and early winter has been documented (Albertson & Evens, 2000). They show strong site tenacity, with scant movement between seasons and a small core-use area (about 0.87 hectare) thej� defend throughout the year (Albertson & Evens, 2000). They spend most of the time hidden in dense marsh vegetation, so they are difficult to observe. When flushed, they will usually fly only a short distance before landing, and then frequendy they can be approached. They are more likely to walk or run than fly, and generally walk upright. To evade discovery, they will freeze, hiding in small sloughs or under overhangs. They run or hide from predators. They swim oniy to cross sloughs or escape imminent threats at high tide, although they swun well. The birds can produce several sounds; the most common is a series of keks or claps (Goude/USFWS, 2002). Rails call to contact each other, advertise breeding status, and defend their nesting territories; if rails are too far apart to hear each other, they may not be able to find a mate or breed (http://desEba�fws$ov/Archives/Cla��er/carail2 htm). They mosdy vocalize during the night (Harvey, 1990, in LSA, 2004), at twilight, and before sunrise (Harvey-CDFG). Ecological threats The principal ecological threat to California clapper rails today is the loss and fragmentation of salt marsh habitat. Tidal marshes in San Francisco Bay have been reduced from historical conditions by 84 percent since 1850 (193,800 acres in 1850; about 30,100 acres today). Remaining Bay Area marshlands are frequently deemed unsuitable habitat for the clapper rail due to their small size, geographic separation from other habitats, lack of natural transition zones between the marsh and upland habitat, lack of tidal channel systems and other microhabitat features, and proxirnin� to urban and industrial development. Simularion models cited by Albertson & Evens (2000) demonstrate that populations of fewer than 10 pairs (in one model) to 25 pair (in another model) are inherendy unstable and could tend toward extinction; hence subpopulation persistence m�- depend on the contiguity of marsh parcels that would facilitate the ability of rails to disperse among sites r�ddiuonall5�, in the South Bay, tidal amplitudes are greater than in San Pablo or Suisun bays, so many tidal marshes become completely submerged during high tides, which limits escape habitat for the birds, potentially resulting in higher predation rates and more nesting failures (CDWR-IEP). �dditionall}�, continued diversion of freshwater inflow from north San Francisco Bay, contamination from urban runoff, industrial discharges, and sewage effluent, and a progressive rise in sea level ma}' impact clapper rails (CDWR-IEP). Conversion of salt marshes to brackish marshes resulting from freshwater discharge from sewage ueatment plants is another impact, creating lower quality habitat. Invasion of non-native plant species, especially smooth cordgrass (Spartina alternif!lora) and its hybrids, can result in degradation of habitat. Smooth cordgrass invasion causes excessive sedimentation, which can clog tidal sloughs used for foraging. The San Francisco Estuary Invasive Spartina Project is a coordinated regional effort among local, state and federal organizations dedicated to preserving coastal biological resources through the elimination of inuoduced species of Spartina (cordgrass). Cordgrasses are highly aggressive invaders that significandy alter both the physical structure and biological composition of our tidal marshes, mudflats and creeks (www.spartina.or�. Maps on the Spartina Project website indicate that colonies of introduced Spartina occur in the viciruty of Redwood Shores and Bair Island. Appendix G of the Final Programmatic EIS/EIR for the Spartina Project (2003) identifies Best Management Practices for avoiding and rrunimizing indirect unpacts from Sparana control activities on the California clapper rail. In a Biological Opinion regarding the Redwood Shores Levee Rehabilitation Project, the USFWS stated in 1996 that mercury accumulation in eggs was "perhaps the most significant contaminant 3