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California clapper rail

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Title: California clapper rail  
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Subject: Dumbarton Bridge (California), San Francisco Bay, San Francisco Peninsula, Monterey, California, San Mateo, California, San Pablo Bay, California Coastal Conservancy, Bair Island, Richardson Bay, Sonoma Creek
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California clapper rail

California Clapper Rail
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Gruiformes
Family: Rallidae
Genus: Rallus
Species: R. longirostris
Subspecies: R. l. obsoletus
Trinomial name
Rallus longirostris obsoletus
Ridgway, 1874

The California Clapper Rail (Rallus longirostris obsoletus) is an endangered subspecies of the Clapper Rail (R. longirostris). It is found principally in California's San Francisco Bay, and also in Monterey Bay and Morro Bay. A member of the rail family, Rallidae, it is a chicken-sized bird that rarely flies.

Like other subspecies of Clapper Rail, this form has a long, downward curving bill and is grayish brown with a pale chestnut breast and conspicuous whitish rump patch. The population levels of the California Clapper Rail are precariously low due to destruction of its coastal and estuarine marshland habitat by prior land development and shoreline fill. It has year-long, circadian activity and is most vocal nocturnally and crepuscularly.[1]

Habitat

The California Clapper Railer forages at the upper end of, along the ecotone between mudflat and higher vegetated zones, and in tidal sloughs. Mussels, clams, arthropods, snails, worms and small fish are its preferred foods, which it retrieves by probing and scavenging the surface while walking. The bird will only forage on mudflats or very shallow water where there is taller plant material nearby to provide protection at high tide. At such high tides it may also prey upon mice, and has been known to scavenge dead fish.[2]


The largest population of California Clapper Rails is in San Francisco Bay, where a total of about 3000 are resident. The photo above right was taken of a California Clapper Rail at the San Francisco Bay perimeter near the Dumbarton Bridge; the Don Edwards San Francisco Bay National Wildlife Refuge in the area provides protected habitats for this and other native species. Other frequent sightings of this species around the San Francisco Bay include the Napa Sonoma Marsh, Bothin Marsh in Mill Valley, Gallinas Creek in San Rafael, Arrowhead Marsh and Damon Marsh in Oakland, the Palo Alto baylands,[3] Charleston Slough in Mountain View, Seal Slough in San Mateo and Belmont Slough.

For cover the California Clapper Rail seeks out emergent wetland dominated by pickleweed and cordgrass, or brackish emergent wetland with those two plants plus bulrush. It is not clear whether it requires any source of fresh water. Although not migratory in coastal wetlands, this species disperses juveniles into freshwater wetlands in late August through October. The California Clapper Rail has been observed to forage in or near relatively disturbed areas, leading one to deduce the importance of protecting even numeral marsh areas; for example this species was seen foraging in a small mudflat area within Seal Slough in San Mateo, three miles from the nearest known breeding area in Belmont.[4]

Breeding

The California Clapper Rail breeds in the San Francisco Bay from mid-March through July, with peak activity in late June. During this breeding season the bird density was approximately 0.1 to 0.6 individuals per acre; outside of breeding season densities decline to 0.04 to 0.40 individuals per acre.[5] The twig nest is placed low sometimes among plant roots, and three purple-spotted buff eggs are laid. Eggs are produced in clutches of four to fourteen, with an average yield of 7.6. The incubation period is 18 to 29 days, and the hatching success is 38%, notably less than the similar Light-footed Clapper Rail indigenous to southern California.

Comparison to some other subspecies

A close relative of the California Clapper Rail is the Light-footed Clapper Rail, Rallus longirostris levipes, a U.S. federal and California state listed endangered subspecies that ranges from Santa Barbara County to the extreme north of the Mexican coast of the Pacific Ocean.

Other races of Clapper Rail are found along the east coast of North America, where populations are stable although numbers have declined due to habitat loss, the coasts and some islands of the Caribbean, and across northern South America to eastern Brazil. The Trinidadian subspecies, R. l. pelodromus, is more heavily marked with black above than any of the other Clapper Rail forms.[6]

References

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