Conservation and Management

Shooting And Trapping

Extremely abundant in early 1900s, and hunted for food and profit; tens of thousands of birds taken in 2 d in 1896 in New Jersey (Forbush 1925), and as many as 200 birds/d taken by many market hunters in San Francisco Bay, CA (U.S. Dept. of the Interior 1991). Annual harvest in Virginia in 1922 estimated at 25,000 birds (Forbush 1925). Currently on list of game birds in all coastal eastern states from Rhode Island to Texas, except New York (Eddleman and Conway 1994). Assessment of number taken per year unreliable. Past estimates were based on number taken by waterfowl hunters, which may represent only 60% of harvest and group Clapper Rail with King and Virginia rails (Banks 1979, Martin 1979). These data show combined harvest of 100,983/yr from 1964 to 1986 (95% CI, 74,100–127,400). State estimates of harvest (1987–1988 in Louisiana, 1990–1991 for other states) available only for Louisiana (20,000), Virginia (9,549), Texas (1,200), New Jersey (800), and Maryland (200; Eddleman and Conway 1994).

Harvest size highly dependent on timing of fall migration in north, because few birds may be available for hunting in years when migration begins before 1 Sep. Hunting pressure heaviest in New Jersey, S. Carolina, and Georgia. Season opening dates ranged from 19 Aug (Virginia) to 19 Sep (Louisiana) in 1990. Bag limits liberal (10–15 daily), but few hunters take Clapper Rails (Eddleman and Conway 1994). Hunting season lasts 2.0–2.5 mo in most states.

Effects of harvest unknown, but probably minimal because of small number of hunters, timing of seasons after peak of migration, difficulty of hunting rails, and tendency of rails to run rather than flush (Eddleman et al. 1988). Most state biologists responding to survey indicated little need for change in existing regulations, although 3 indicated that reducing bag limits might be warranted because of lack of information about population biology (WRE).

Clapper Rails occasionally caught and killed in traps set for fur-bearing animals such as mink or muskrats (Simmons 1914, Eddleman et al. 1988). This probably has little effect on populations, however. Eggs once gathered in large numbers for food in southern states (Forbush 1925).

Pesticides And Other Contaminants/Toxics

Coastal wetlands in which Clapper Rails occur serve as settling basins for a wide variety of toxic materials (Eddleman et al. 1988). Specific effects of most of these materials on Clapper Rails unknown. Captives fed DDT are relatively resistant to it; show no immediate effects (Van Velzen and Kreitzer 1975). Long-term reproductive effects unknown.

Eggs collected in New Jersey, Virginia, and S. Carolina in 1972–1973 had residues of DDE and PCBs (ranging from 0.10 to 1.3 ppm), but showed no eggshell thinning (Klaas et al. 1980). Mercury contamination in breast muscle of 93.5% of birds collected near Brunswick, GA, exceeded Food and Drug Administration’s tolerance level of 0.5 ppm (ranging from 0.01 to 9.45 ppm wet weight; Odom 1975). Residues of DDD, DDT, DDE, dieldren, heptachlor epoxide, and PCBs were found in body tissues of 27 birds from Louisiana, but all were below levels that might cause concern (Roth 1972). Mercury levels in obsoletus eggs from San Francisco Bay, CA, were higher than those from N. Carolina, and within the range associated with developmental abnormalities in other birds (Lonzarich et al. 1992). Selenium levels were also elevated in obsoletus eggs, but lower than values causing reproductive effects in American Coots (Fulica americana). Two of 7 eggs of levipes from s. California analyzed in 1983 had DDE levels of 9.6 and 6.8 ppm, respectively—within the range that causes poor reproduction in other species (Eddleman et al. 1988). Several compounds found in chlordane (oxychlordane, heptchlor epoxide, trans- and dis-nonachlor, MC-2, and MC-5) were detected in levipes eggs in s. California (Jarman 1991). MC-2 bioaccumulated to greatest degree. Selenium accumulates in sediments and crayfish prey of yumanensis in backwater habitats on lower Colorado River in Arizona and California (mean liver selenium level 25.3 ppm dry weight ± 5.9 SD, n = 5; Rusk 1991). This level unlikely to cause adult mortality, but conveys moderate to high risk of hatching defects in chicks.

Collisions With Stationary/Moving Structures Or Objects

Sometimes collides with TV towers, lighthouses, telephone wires, or fences (Emerson 1904, Forbush 1925, Murray 1929, Taylor and Kershner 1986, Allen and Ramirez 1990). Timing of strikes corresponds with fall migration, spring migration, or fall dispersal (Orr 1939). Sometimes hit by vehicles if roads bisect marshes (Zembal et al. 1989). Vehicle collisions accounted for 1.5% of 156 recoveries of birds banded in New Jersey (Ferrigno 1990).

Degradation Of Habitat

Interference with tidal flow is the most common mode of habitat degradation for Clapper Rails (Meanley 1985, Eddleman and Conway 1994). Effects of this problem include drying of habitats such that high marsh or terrestrial plants replace low marsh plants favored for nesting and foraging by Clapper Rails, lowering of salt content, invasion of habitat by common reed (Phragmites australis), or permanent flooding of marshes by construction of impoundments. Nonetheless, large areas of suitable habitat remain on East Coast. Wetlands of Baja California are largely intact, although threatened by resort and industrial development planned by international companies and salt evaporation pond development (Massey and Palacios 1994).

Loss and degradation of habitat because of urbanization in coastal California has been severe (Eddleman et al. 1988); <33% of original habitat in range of levipes remains intact in s. California, although more remains in Mexico. About 80–90% of the original 73,500 ha of marsh in San Francisco Bay, CA, has been filled, destroyed, or diked, and much of the remainder is degraded (U.S. Dept. of the Interior 1991). Former habitat of yumanensis mostly in Colorado River delta, because most wetlands on lower part of river were ephemeral (Ohmart et al. 1975). Much of habitat today consists of marshes formed behind dams from Needles, CA, to Mexican border. Most water reaching Colorado River delta in n. Mexico comes from floodwater, irrigation runoff, and municipal sewage effluent, but these sources do maintain >5,800 ha of yumanensis habitat (Glenn et al. 1996). Much of this habitat is threatened by water diversion to Gulf of California and future disposal of salt into the sources of water from desalinization plant.

Direct Human/Research Impacts

Introduction of exotic mammals such as red foxes, rats, dogs, and cats is a major factor in the decline of obsoletus since 1970, and to a lesser extent, levipes . Harnesses used for attaching radio transmitters may affect survival by interfering with ability to fly (WRE). Nest traps caused 56% of trapped birds to desert nests (Blandin 1963).

Conservation Status

Stable in eastern U.S., provided that wetland degradation ceases. Protected status accorded to Clapper Rails in New York because of lack of information on effects of hunting (WRE). Status and biology of insularum of Florida Keys least known among North American subspecies; status of Central and South American taxa unknown or poorly known (Ripley 1977). Monitoring programs used for other bird species are not effective for wetland species such as Clapper Rails, and valid information on status must await development and implementation of new monitoring techniques (Eddleman and Conway 1994).

Three taxa of Clapper Rail— obsoletus, levipes, and yumanensis —are classified as both state and federally Endangered (Arizona Game and Fish Dept. 1988, California Dept. of Fish and Game 1989, USFWS 1989). Initially, levipes and obsoletus populations declined because of overhunting (Leipsic-Baron 1992). With protection, obsoletus rebounded in numbers, but levipes did not. Past wetland loss and degradation has been severe in coastal California and in Colorado River ecosystem, and all 3 subspecies have declined since 1900 as result of habitat loss. In addition, nearly all habitats of these taxa have contaminants either in water inflows or in sediments. Low fertility and egg-hatching success in northern populations of levipes may be result of contaminants or inbreeding (Eddleman et al. 1988, Fleischer et al. 1995). Very little genetic variation detected in levipes populations, but effects of inbreeding have not been assessed. Numbers estimated at 300–600 pairs in U.S. (Small 1994). Numbers of obsoletus estimated at 4,000–6,000 birds in mid-1970s, 1,000 in mid-1980s, <700 by 1988, <500 by 1991, and by 1996 <300 (U.S. Dept. of the Interior 1991). Remaining yumanensis number about 700 (Shuford 1993, Small 1994). Estimates of genetically effective population size based on mitochondrial DNA microsatellites for levipes (N_e= 174–283) and yumanensis (N_e= 824; Fleischer et al. 1995) lend credence to call-survey estimates.

Measures Proposed And Taken; Effectiveness Of Measures

Continued implementation of wetland protection laws is the most effective conservation technique for Clapper Rails (Eddleman and Conway 1994). Most habitat management programs for coastal subspecies have involved preservation or restoration of tidal flow (Shisler and Schulze 1976, Ferrigno et al. 1987). Tidal restoration of salt hay impoundments, in which areas diked for hay production in New Jersey salt marshes have had tidal flow restored, has improved some marshes for Clapper Rail (Ferrigno et al. 1987). Open marsh water management, used in many eastern salt marshes to control mosquitoes, consists of connecting existing pools in salt marshes to allow fish to move between pools and eat mosquito larvae (Shisler and Schulze 1976, Erwin et al. 1994). Effects of open marsh water management on rails poorly known, although spoil from the ditches may provide additional nest sites for Clapper Rails. Management for levipes in s. California is same as management for Pacific cordgrass (Foin and Benchley-Jackson 1991): Techniques include keeping salt marshes open to tidal flow, restoring potential remaining wetland areas, and expanding efforts to improve habitat where there is the greatest potential for cordgrass enhancement. Habitat acquisition for obsoletus in s. San Francisco Bay, CA, has helped slow population decline (U.S. Dept. of the Interior 1991).

Improved harvest assessment for hunted subspecies is possible with implementation of migratory bird permit requirement for hunting Clapper and other rails (Tautin et al. 1989). Translocations among levipes populations in s. California and from yumanensis to levipes populations have been suggested to increase genetic variation of levipes (Fleischer et al. 1995). Control of nonindigenous predators (red fox) undertaken to increase numbers of obsoletus, and estimates of population in s. San Francisco Bay, CA, doubled in 1993 (from 300 to 600) after predator removal in 1992 (Takekawa 1993). Predator control (domestic cats) also resulted in increased number of levipes at Seal Beach National Wildlife Refuge, CA.

Recommendations for stabilization and increase of yumanensis populations include: increased consideration of the subspecies in management of federal and state wildlife refuges; continued population monitoring; year-round management based on the assumption of year-round residency by the subspecies; water level manipulations on diked impoundments; restoration of wetlands in Colorado River delta; maintenance of irrigation drain water to Cienega de Santa Clara; and careful monitoring of river management and mitigation projects conducted in the habitat (Eddleman 1989, Glenn et al. 1996). Maintenance of existing marshes and creation of new marsh habitats using dikes, impoundments, and reliable sources of water would provide improved nesting and foraging areas for this subspecies (Eddleman and Conway 1994).