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Clapper rail nests are normally built by the males and are described as a "mass" or "heap" of vegetation, deep- cupped and woven to adjoining live plant material in a manner that allows it to float during extreme high tides, although they are somewhat buoyant, they are not sturdy enough to withstand a series of high tides (Zucca 1954 in CDWR -IEP). According to Harvey (1980) and Zembel and Massey (1983), in saline emergent wetlands, the birds nest mostly in lower zones near tidal sloughs and where cordgrass is abundant; nests are constructed as high as necessary to prevent inundation while maintaining sufficient natural vegetation cover. Harvey (CDFG B144 online) reports that the clapper rail builds a platform hidden by a canopy of woven cordgrass stems or pickleweed and gumweed, but may use dead drift vegetation as a platform. In brackish to fresh water, nests may be built in dense cattail or bulrush. Diurnal cycle. Peak California clapper rails activity occurs in the early morning and late evening, when they forage; frequently they roost at high tide during the day (USFWS /Sacramento). 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) they 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 frequently 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 only to cross sloughs or escape imminent threats at high tide, although they swim 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: / /desfbay.fws.gov /Archives /Clal2per /carail2.htm They mostly 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 proximity to urban and industrial development. Simulation models cited by Albertson & Evens (2000) demonstrate that populations of fewer than 10 pairs (in one model) to 25 pair (in another model) are inherently unstable and could tend toward extinction; hence subpopulation persistence my depend on the contiguity of marsh parcels that would facilitate the ability of rails to disperse among sites Additionally, 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). Additionally, 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 may impact clapper rails (CDWR -IEP). Conversion of salt marshes to brackish marshes resulting from freshwater discharge from sewage treatment plants is another impact, creating lower quality habitat. 3