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Treaty Act of 1918 prohibited clapper rail hunting and its numbers rebounded. However,
<br />destruction of much of the salt marsh habitat for the bird caused its numbers to dwindle
<br />precariously. Of the 193,800 acres of tidal marsh bordering San Francisco Bay in 1850, only slightly
<br />more than 30,000 acres remain. When listed as endangered in 1970 (U.S.) and 1971 (CA), the
<br />California clapper rail population was estimated at 4,200 to 6,000 birds; the all-time historical low is
<br />about 500 individuals, with about 300 of these in the south part of San Francisco Bay. The
<br />population has subsequently rebounded (see below) as a result of predator management activities.
<br />The south San Francisco Bay population is now estimated to be between 500 and 600 birds, with
<br />some 200 to 300 pairs occurring in the north part of San Francisco Bay. Likely causation of the
<br />diminution of the population is a combination of the fragmentation of the clapper rail's habitat and
<br />increased predation, described in more detail below (CDWR -IEP).
<br />Habitat California clapper rail habitats typically have the following features: (1) marshes that
<br />support an extensive system of tidal sloughs having direct tidal circulation sufficient to allow the full
<br />tidal cycle, (2) pickleweed (Salicornia vir�inica) is the predominant vegetation with extensive Pacific
<br />cordgrass (Spartina foliosa) at lower marsh elevations, (3) abundant, dense high marsh cover (tall
<br />stands of pickleweed, gumplant [Grindelia spp.], and wrack), and (4) abundant invertebrate
<br />populations. The preferred habitat is Spartina marsh (CDWR -IEP), which dominates the middle
<br />marsh zone in the south Bay (USFWS -Sac). Optimum California clapper rail habitat needs both high
<br />marsh, with dense vegetation for nesting, and low marsh, with sparse vegetation and tidal sloughs for
<br />foraging (Albertson, 1996). Additionally, buffer areas between marsh and upland are critical aspects
<br />of rail habitat, for use as escape cover from predators during high tide (Albertson & Evens, 2000).
<br />Feeding A 1941 study by Moffitt (cited in CDWR - IEP) found that by volume, most ( >85
<br />percent) of the stomach contents of clapper rails was animal matter, 14.5 percent was vegetable
<br />matter. Of the animal matter, 56.5 percent was plaited horse mussel (Modiolus volsetta demissus); the
<br />remainder comprised spiders (15 percent), macoma clams (7.6 percent), mud crabs (3.2 percent), and
<br />bones from brush rabbits, the latter presumably from carrion. The California clapper rail feeds by
<br />walking a few steps, thrusting its beak into the mud up to eye level, then walking a few more steps
<br />and repeating its probing (Wilbur and Tomlinson, 1976, cited in CDWR IEP). CDFG cites Zembel
<br />and Massey (1983) indicating that the clapper rail forages in higher marsh vegetation, along the
<br />mudflat /vegetation interface, and along tidal creeks; the rail "gleans, pecks, probes, and scavenges
<br />from [the] surface," and takes mice during high tides, and may scavenge dead fish
<br />( www.dfg .ca.gov /whdab /html /B144.htm1 Another writer indicates that clapper rails, although
<br />opportunistic feeders, prefer crabs and crayfish (Garrison, 2000).
<br />Reproduction The breeding season begins in February, when pair bonds are typically established
<br />(USFWS- Goude, 2002), with nesting extending from mid -March into August. The breeding season
<br />is typically considered to end at the end of August, by which time the eggs laid during re- nesting
<br />efforts have hatched and the young are mobile (USF vVS, Sacramento on line). Clutch sizes are
<br />variously reported as ranging from 5 to 14 eggs (USFWS -Sac), 6 to 8 (Garrison, 2000), 6 to 10
<br />(CDWR -IEP), and an average of 7.6, with a hatching success rate in the Bay Area of 38 percent
<br />(Harvey, 1980, in LSA, 2004). Both the male and female incubate the eggs for 18 to 29 days (LSA,
<br />2004). The young are precocial, i.e., they are covered with down and capable of moving about when
<br />hatched (www.pwrc.usgs.gov). The young usually accompany their parents for about 8 weeks,
<br />learning to forage on their own. They fledge at about 10 weeks (Albertson & Evens, 2000).
<br />Garrison states (2000) that high tides and heavy spring rains may destroy up to half of clapper rail
<br />nests, but that the clapper rail will re -nest up to five times.
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