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<br /> problem affecting clapper rails in San Francisco Bay, with the south Bay containing the highest
<br /> mercury levels." On the basis of data the Service collected in 1991 and 1992 in the southem portion
<br /> of the estuary, the Service concluded that "the current accumulation of inercury in rail eggs occurs at
<br /> potenaally hazmful levels"; the mean percentage of non-viable eggs was 29 percent (Medlin/USFWS,
<br /> 199G).
<br /> A 1992 study wherein 22 failed California clapper rail eggs from four south Bay tidal mazshes were
<br /> analyzed for organochlorines and eggshell thicknesses were measured. The study found that
<br /> concentrations of all organochlorines except PCBs appeared to have declined since the mid 1980s,
<br /> and eggshell thicknesses were statistically indistinguishable from those of pre-1932 museum eggs
<br /> (Schwarzbach et al.).
<br /> Predators Dikes and levees serve as corridors for predators to access clapper rail habitats. Most
<br /> predauon occurs during the higher tides, when tidal channels are full of water and much of the
<br /> vegetation is flooded; very high tides are more common in the wintertime (Albertson, 1996). At least
<br /> 12 native and 3 non-native species prey on the clapper rail throughout its lifespan (Medlin/USFWS,
<br /> 1996). The non-native red fox (Vupes Norway rat (Battu.r norvegicu.r), and feral cats (Felr.r
<br /> dome.rticu.r), are particular threats. To manage red fox predation, deemed potentially the most serious
<br /> threat to clapper rail populations, the San Francisco Bay National Wildlife Refuge in 1991
<br /> unplemented a predator management program, which has been somewhat successful. The program
<br /> includes predator barriers, removal, and habitat management to make it less suitable for the
<br /> predators. In addition, riprap installed along shorelines provides habitat for Norway rats, which prey
<br /> on clapper rail eggs. Urban development close in to salt marsh habitat has increased predation by
<br /> native raccoons, and electric power transmission lines that cross marsh habitats, provide hunting
<br /> perches for raptors.
<br /> The U.S. Department of Agriculture Animal and Plant Health Inspections Service Wildlife Services
<br /> (VC'S) entered into a cooperative agreement with the city of Redwood City to conduct predator
<br /> management activities at Redwood Shores Peninsula to protect the California clapper rail and salt
<br /> marsh harvest mouse from mammalian predators. The agreement is part of a requirement of the
<br /> USFVC�S Biological Opinion dated September 5, 1996, regarding the Endangered Species Formal
<br /> Consultation on the Redwood Shores Levee Improvement Project (Medlin/USFWS, 1996).
<br /> Predator management activities began May 22, 2000, and have continued to the present. The
<br /> following table summarizes information on the predators trapped by WS, based on periodic letter
<br /> reports from WS to Mr. Peter Vorametsanti, Senior Civil Engineer, Redwood City (WS, 2000a,
<br /> 2000b; 2001, 2002, 2004a, 2004b):
<br /> Mammalian Predators Trapped at Redwood Shores Peninsula,
<br /> May 22, 2000 — December 31, 2003
<br /> Inclusive Dates Number � Type of Disposition of Predators (following
<br /> Predators Tra ed trans ort to PHS *
<br /> 12 feral cats (Feli.r 2 cats returned to owners, 3 cats adopted, 5
<br /> FY 2000 (October 1, �mertrcu,r), 4 raccoons cats euthanized, 1 pending at time of report, 1
<br /> �999 — September 30, �Prncyon lotor), & 1 striped escaped; 3 raccoons & 1 skunk microchipped
<br /> 000) and released w/in 3 miles of capture site per
<br /> skunk (Mephiti.r mephitia).
<br /> CDFG oli ; 1 raccoon euthanized.
<br /> FY 2001 (October 1, 1 cat returned to owner, 3 cats adopted, 1
<br /> 2000 — September 30, 6 feral cats, 2 raccoons. injured cat euthanized; 1 raccoon euthanized,
<br /> 2001 as it had been ca tured the recedin ear; 1
<br /> 4
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