By Tim Dodson
The California clapper rail (Rallus longirostris obsoletus) is the focus of this edition’s “Species Spotlight.” The California clapper rail belongs to the order Gruiformes, in the family Rallidae, which includes rails, gallinules, and coots. The genus Rallus consists primarily of marsh-dwelling birds with short rounded wings, large feet, and long toes.
California clapper rails are fully dependent on salt marsh habitat and occur almost exclusively in tidal salt and brackish marshes with unrestricted daily tidal flows, adequate invertebrate prey food supply, well developed tidal channel networks, and suitable nesting and escape cover that can be used as refugia during extreme high tides.
California clapper rails eat spiders, amphipods, yellow and striped shore crabs, clams (Macoma balthica), and the introduced horse mussel. These birds nest from mid-March into July with nesting peaks in late April–early May and late June–early July. The second peak may include late nesters and pairs attempting to overcome initial nesting failure.
Historically, the range of the California clapper rail may have extended from Humboldt Bay to Morro Bay. Thousands of California clapper rails were eliminated by market hunters from the time of the Gold Rush until the passage of the Weeks-McLean Law in 1913, which was a precursor to the Migratory Bird Treaty Act (MBTA). The MBTA was designed to stop commercial hunting and illegal shipment of migratory birds from one state to another.
The current distribution is limited to the salt marsh habitats in the San Francisco Bay Delta (SFBD) Ecoregion. California clapper rail is a true endemic to this area meaning
it occurs here and nowhere else. Originally, the salt marshes of South San Francisco Bay had the largest populations of California clapper rails. Now, remaining populations are found in remnant salt marshes such as those on Bair and Greco Islands, along Coyote Creek, and throughout the marshes in the Don Edwards San Francisco Bay National Wildlife Refuge. Smaller populations are located in western Contra Costa, eastern Marin, and northern Alameda Counties.
California clapper rails are also found in northern San Pablo Bay, along the Petaluma River as far north as Schultz Creek, along major creeks and marshes in both Sonoma and Napa Counties and on Bull Island on the Napa River. The extension of range further east in Suisun Marsh and northern Contra Costa County may bear some relationship to reductions in Sacramento-San Joaquin Delta freshwater outflow and concomitant increases in salinity.
California clapper rails typically utilize salt marshes dominated by both pickleweed (Salicornia virginica) and pacific cordgrass (Spartina foliosa). California clapper rails use a network of small tidal sloughs for foraging and quick escape. They construct nests near tidal sloughs (within 10 meters), canopied with either pickleweed or cordgrass, sometimes gum-plant, salt grass, or drift materials. Density of cover, floatability of materials, height above tides, and annual weather changes are all variables of successful nesting. California clapper rails also construct “brood nests” on higher ground to protect nests and young from storm influenced tides. These are usually simple floatable, platforms of twigs or stems, without a canopy.
The California clapper rail is listed as an Endangered Species under the Federal and State Endangered Species Act and as a Fully Protected Species under the California Fish and Game Code. As described in the 2010 U.S. Fish and Wildlife Service Draft Recovery Plan for Tidal Marsh Ecosystems of Northern and Central California, lack of extensive blocks of tidal marsh with functional habitat structure is the ultimate limiting factor for the species’ recovery. In addition, vulnerability to predation by native and non-native predators is exacerbated by reduction of California clapper rail habitat now occurring predominately as narrow and fragmented patches close to expanding urban areas.
Diking, dredging and filling the marsh for conversion to agriculture, urban development and salt production have reduced total marshes in the San Francisco Bay by 84% or more. Levees provide artificial access for terrestrial predators displacing optimal cover of high marsh vegetation. The predators of adult rails include cats, other mammals, northern harriers, red-tailed hawks, and peregrine falcons. The presence of non-native red foxes is further impacting the rail. Norway rats prey upon young rails. In addition, contaminants, particularly methylmercury, have been identified as a significant factor affecting viability of California clapper rail eggs.
The rapid invasion of San Francisco Bay by exotic Spartina alterniflora (smooth cord grass) and its hybrids with the native S. foliosa (Pacific cordgrass) has presented a unique challenge. Since the Invasive Spartina Project (ISP) began in 2000 with the intent of eliminating introduced species of Spartina from the San Francisco Bay Estuary, more than 75 ISP partners have successfully reduced the infestations by 96% from the peak of over 800 net acres in 2006. Clapper rail population trends are stable at sites where non-native Spartina has undergone continuous control and where non-native Spartina has been reduced to insignificant levels.
In the long run, the control of Spartina should benefit the rail by creating a more natural native marsh. However in the near-term, eradication poses a severe threat to California clapper rails and their habitat because of the temporal loss of cover due to the lag time between eradication of exotic cordgrass and regrowth of native cordgrass. The ISP is undergoing active revegetation at treatment sites that is designed to enhance foraging, nesting and high tide refuge habitat for the California clapper rail by carefully considering this timing issue.
As described in the another article in this current newsletter, under the SWAP 2015 Update, the SFBD Conservation Unit team has developed conservation strategies that protect existing marshes, streamline restoration projects, control invasive species, as well as that support education program to enhance the public’s appreciation of the marsh and the California clapper rail, all of which are meant to benefit this important and unique species.
NOTE: the following were used as references for this article:
The United States Fish and Wildlife Service’s 5-Year Review: Summary and Evaluation for the California Clapper Rail
United States Environmental Protection Agency’s Endangered Species Fact Sheet for the California Clapper Rail