California Clapper Rail

Rallus longirostris obsoletus

Description

The California clapper rail is one of the largest species of the genus Rallus, measuring 13-19 in (32-47 cm) from bill to tail. It has a henlike appearance with strong legs, long toes, and a long bill. It has a cinnamon-colored breast, dark flanks with white bars, and olive-brown upper parts.

The California clapper rail was first described as a king rail, R. elegans var. obsoletus, in 1834, and in 1880 the species was reclassified as a new species of clapper rail, R. obsoletus. In 1926, A. J. Van Rossem combined the Pacific coast clapper rails into one species, and in 1977, S. Ripley revised the species again, identifying 24 separate subspecies in North, Central, and South America, and the Caribbean.

Behavior

The California clapper rail is secretive and difficult to flush. Once flushed, however, it can frequently be closely approached. Birds accustomed to humans, such as those at the City of Palo Alto Bay-lands, continue to feed despite people on nearby boardwalks. When disturbed, clapper rails usually fly only a short distance before landing. Clapper rails nest from mid-March to July, with peaks of activity in early May and again in early July. The female lays a clutch of five to nine eggs, and both parents take turns incubating for 23-29 days. The eggs are light tan or buff-colored with cinnamon-brown or dark lavender spotting at the broader end. California clapper rails feed mostly on mussels, spiders, clams, and small crabs.

Habitat

The clapper rail constructs its nest in marsh-lands near tidal ponds, arranging plants or drift material over the nest as a canopy. It will often construct a brood nest on higher ground to shelter the young from storm tides; this is usually a simple platform of twigs without a canopy. Marsh vegetation includes cordgrass, pickleweed, gum-plant, and salt grass. Clapper rails in the South San Francisco Bay marshes prefer to nest in stands of cordgrass but build their nests mostly of pickle-weed.

Distribution

The salt marshes of South San Francisco Bay, including portions of San Mateo, Santa Clara, and Alameda Counties, once supported the largest populations of California clapper rails. Smaller populations were found along western Contra Costa County, eastern Marin County, and near Petaluma in Sonoma County. Some records indicate that there may have been a sizable population in Napa Marsh in western Napa County. Marshes south of San Francisco Bay in Elkhorn Slough and others adjacent to Monterey Bay also once had small populations. The eastern limit of the historic range is believed to have been Southampton Bay in Solano County. The California clapper rail is now restricted to the San Francisco Bay ecosystem. The species has been in serious decline for decades; by 1988, it had plummeted to less than 700 birds—a decline of more than a 30% in two years. Predation by other species, marsh erosion, and water pollution threaten the remaining California clapper rails in South San Francisco Bay. Of 155 eggs from 24 ran clutches surveyed by three refuge biologists in 1989, 56% were lost to predation or flooding, or failed to hatch. Winter surveys in 1989 in the bay estimated 400-500 birds. A 1990 winter census by the U. S. Fish and Wildlife Service (FWS) and the California Department of Fish and Game (CDFG) indicated that although the rail populations appeared more stable along the western shoreline of South San Francisco Bay (where the red fox, a primary predator, apparently has not yet become well-established), populations along the eastern shoreline within the refuge continued to decline. Several populations in important marshes averaged only 50% of the 1989 count. In South San Francisco Bay, clapper rail populations are found in remnant salt marshes, such as Bair and Greco Islands in San Mateo County, Dumbarton Point in Alameda County, and Santa Clara County coast-lands. In San Mateo County, rails are found as far north as San Bruno Point. Scattered individuals nest near creek mouths in northern Alameda County, western Contra Costa County, and eastern Marin County. A small breeding population may also still exist in Richardson Bay in Marin County. Other small populations are found in northern San Pablo Bay, along the Petaluma River as far north as Schultz Creek, along most major tidal marshes and creeks in Sonoma and Napa Counties, and at Bull Island on the Napa River.

Threats

Around the end of the nineteenth century, indiscriminate hunting initiated a clapper rail decline. A newspaper account from 1897 mentions some 1,000 rails of various species killed during a single week. After the Migratory Bird Treaty Act was passed in 1913, prohibiting such wholesale slaughter, rails regained some of their former abundance. But wetland destruction had begun. Marshlands were lost first to agriculture, then to urban development, airports, and salt evaporation ponds. Two hundred years ago the San Francisco Bay ecosystem contained about 283 sq mi (734 sq km) of tidal marsh; by the late 1990s, only 59 sq mi (152 sq km) remained. This dramatic reduction of marshland has greatly reduced the clapper rail population. One site in Suisun Marsh is largely undisturbed and supports a healthy clapper rail population, but most marshes are degraded in one form or another. Remnant marshes in South San Francisco Bay are bounded by steep earthen levees; upper marsh vegetation has been eliminated, reducing cover for rails during winter flood tides. Adult clapper rails are preyed upon by the northern harrier, red-tailed hawk, and the peregrine falcon (Falco peregrinus ). Young rails and eggs are eaten by Norway rats. The horse mussel is strong enough to trap a clapper rail's foot or beak and may cause some rail deaths.

Conservation and Recovery

Conservation of the rail's marsh habitat has been underway for some time, mostly through land acquisition. Tracts of salt marsh in South San Francisco Bay and San Pablo Bay have been acquired by the National Audubon Society and other organizations. The CDFG has restored marshes in Redwood City. The FWS has established the San Francisco Bay National Wildlife Refuge, while the East Bay Regional Park District has worked to restore marshes on the Hayward shoreline.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Gill, R., Jr. 1979. "Status and Distribution of the California Clapper Rail." California Fish and Game 65: 36-49.

Ripley, S. 1977. Rails of the World: A Monograph of the Family Rallidae. D. R. Godine Publishing, Boston.

U. S. Fish and Wildlife Service. 1984. "The Salt Marsh Harvest Mouse and California Clapper Rail Recovery Plan." U. S. Fish and Wildlife Service, Portland, Oregon.