Ridgway's rail (''Rallus obsoletus'') is a

near-threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of bird. It is found principally in

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...

to southern

Baja California Baja California (; 'Lower California'), officially the Free and Sovereign State of Baja California ( es, Estado Libre y Soberano de Baja California), is a state in Mexico. It is the northernmost and westernmost of the 32 federal entities of Mex ...

. A member of the rail family,

Rallidae The rails, or Rallidae, are a large cosmopolitan family of small- to medium-sized, ground-living birds. The family exhibits considerable diversity and includes the crakes, coots, and gallinules. Many species are associated with wetlands, althoug ...

, it is a chicken-sized bird that rarely flies. This species is closely related to the

clapper rail The clapper rail (''Rallus crepitans'') is a member of the rail family, Rallidae. The taxonomy for this species is confusing and still being determined. It is a large brown rail that is resident in wetlands along the Atlantic coasts of the easte ...

, and until recently was considered a subspecies. It has a long, downward curving bill and is grayish brown with a pale chestnut breast and conspicuous whitish rump patch. The population levels of Ridgway's 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 A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous) and responds to ...

activity and is most vocal

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

ly and

crepuscular In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal, vespertine, or both. This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylig ...

ly. The Ridgway's rail pertains to the

family within order

Gruiformes The Gruiformes are an order (biology), order containing a considerable number of living and extinct bird family (biology), families, with a widespread geographical diversity. Gruiform means "crane-like". Traditionally, a number of wading and t ...

. The California subspecies naturally exists in tidal salt and brackish marshes. These ecosystems are subjected to freely flowing daily tidal flows, a sustainable amount of prey food supply consisting of invertebrates, advanced tidal waterway systems, and apt nesting areas and covered spaces that serve as protection during dangerous high tides. The species was officially named by ornithologist James Maley after the renowned ornithologist

Robert Ridgway Robert Ridgway (July 2, 1850 – March 25, 1929) was an American ornithologist specializing in systematics. He was appointed in 1880 by Spencer Fullerton Baird, secretary of the Smithsonian Institution, to be the first full-time curator of bird ...

Habitat

Ridgway's rail forages at the upper end of, along the

ecotone An ecotone is a transition area between two biological communities, where two communities meet and integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and gras ...

between mudflat and higher vegetated zones, and in

tidal Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...

slough Slough () is a town and unparished area in the unitary authority of the same name in Berkshire, England, bordering west London. It lies in the Thames Valley, west of central London and north-east of Reading, at the intersection of the M4 ...

Mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two she ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

s and small fish are its preferred foods, which it retrieves by probing and scavenging the surface while walking. The bird will only forage on

mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...

s 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. One of the largest population of Ridgway's rails is in San Francisco Bay, where a total of about 1100 are resident.L. Liu et al., "California Clapper Rail (Rallus longirostris obsoletus) Population monitoring: 2005–2011" PRBO Technical Report to the California Department of Fish and Game. (2012)
/ref> In the past, however, its geographic range spanned more than 90% of the range of the San Francisco Bay. The photo above right was taken of a Ridgway's rail at the San Francisco Bay perimeter near the Dumbarton Bridge; the

Don Edwards San Francisco Bay National Wildlife Refuge Don Edwards San Francisco Bay National Wildlife Refuge (DESFBNWR) is a United States National Wildlife Refuge located in the southern part of San Francisco Bay, California. The Refuge headquarters and visitor center is located in the Baylands dis ...

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 The Napa Sonoma Marsh is a wetland at the northern edge of San Pablo Bay, which is a northern arm of the San Francisco Bay in California, United States. This marsh has an area of 48,000 acres (194 km2), of which 13,000 acres (53 km2) are ...

Bothin Marsh Bothin Marsh is a wetland in Marin County, California. Parts of the wetlands are in the Bothin Marsh Open Space Preserve, a regional park. Natural history The marsh, positioned at the northern arm of Richardson Bay is fed by Arroyo Corte Madera ...

Mill Valley Mill Valley is a city in Marin County, California, United States, located about north of San Francisco via the Golden Gate Bridge and from Napa Valley. The population was 14,231 at the 2020 census. Mill Valley is located on the western and ...

, Gallinas Creek in San Rafael,

Arrowhead Marsh Arrowhead Marsh is a wetlands habitat made of tidal mud flats in Martin Luther King, Jr. Shoreline in Oakland, California. It is an important stop on the Pacific flyway and is habitat for important endangered species especially the Salt Marsh Harv ...

and

Damon Marsh The Damon Marsh is a tidal wetland at the northern edge of San Leandro Bay in Oakland, California, USA. There is a paved long shoreline trail along the waterfront to allow visual access to the San Leandro Bay and through the marsh itself. One en ...

Oakland Oakland is the largest city and the county seat of Alameda County, California, United States. A major West Coast port, Oakland is the largest city in the East Bay region of the San Francisco Bay Area, the third largest city overall in the Bay A ...

, the

Palo Alto Palo Alto (; Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a coastal redwood tree known as El Palo Alto. The city was estab ...

baylands,

Charleston Slough Charleston Slough is a former Leslie salt pond that is now reverting to marsh on the western shore of San Francisco Bay. Environmental damage and recovery In 1975 Leslie Salt owned the slough and used it for its salt water evaporation operatio ...

in Mountain View,

Seal Slough Seal Slough, also known as Marina Lagoon, is a narrow winding tide, tidal channel through a tidal marsh in San Mateo, California, San Mateo and Foster City, California. This River delta, slough has been the object of a wetland restoration ecology, ...

in San Mateo and Belmont Slough. For cover, Ridgway's rail seeks out emergent wetland dominated by

pickleweed Pickleweed is a common name used for two unrelated genera of flowering plants: *'' Batis'', family Bataceae *''Salicornia ''Salicornia'' is a genus of succulent, halophytic (salt tolerant) flowering plants in the family Amaranthaceae that gro ...

and

cordgrass ''Spartina'' is a taxon of plants in the grass family, frequently found in coastal salt marshes. Its species are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Europe, north ...

, or brackish emergent wetland with those two plants plus

bulrush Bulrush is a vernacular name for several large wetland grass-like plants *Sedge family (Cyperaceae): **''Cyperus'' **''Scirpus'' **'' Blysmus'' **''Bolboschoenus'' **''Scirpoides'' **''Isolepis'' **''Schoenoplectus'' **''Trichophorum'' *Typhacea ...

. It is not clear whether it requires any source of fresh water. Although not migratory in coastal

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

s, this species disperses juveniles into freshwater wetlands in late August through October. Ridgway's rail has been observed to

forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used m ...

in or near relatively disturbed areas, leading one to deduce the importance of protecting even numeral

marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...

areas; for example this species was seen foraging in a small mudflat area within

in San Mateo, three miles from the nearest known breeding area in Belmont.

Feeding and ecology

The omnivorous Ridgway's rail eats many things, including clams, crabs, mussels, and occasionally small rodents and birds.

Breeding

By mid-February, nest building has begun. The Ridgway's rail then breeds (California rail subspecies) in the San Francisco Bay from mid-March through August, with peak activity in late June. During this

breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Animal husbandry, through selected specimens such as dogs, horses, and rab ...

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. The twig nest is placed low, sometimes among plant roots, and purple-spotted buff eggs are laid. Eggs are produced in

clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...

es 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 rail indigenous to southern California. Incubation is shared between both the male and female Ridgway's rail.

Subspecies

*''R. o. obsoletus'', formerly California clapper rail, nominate subspecies US-FWS: Species Profile for California Clapper rail (''Rallus longirostris obsoletus'')
/ref> *''R. o. levipes'', light-footed rail, a U.S. federal and California state listed endangered subspecies that ranges from

Santa Barbara County Santa Barbara County, California, officially the County of Santa Barbara, is located in Southern California. As of the 2020 census, the population was 448,229. The county seat is Santa Barbara, and the largest city is Santa Maria. Santa Barba ...

to the extreme north of the

Mexican Mexican may refer to: Mexico and its culture *Being related to, from, or connected to the country of Mexico, in North America ** People *** Mexicans, inhabitants of the country Mexico and their descendants *** Mexica, ancient indigenous people ...

coast of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

. *''R. o. yumanensis'', Yuma rail, southeastern

and southern

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

, to northwestern MexicoBLM: Yuma Clapper Rai (''Rallus longirostris yumanensis'')
/ref> *''R. o. beldingi'', Belding's rail, southern

References

External links

* {{Taxonbar, from=Q22003908 Birds described in 1874 Endemic fauna of California Fauna of the San Francisco Bay Area Native birds of the West Coast of the United States Natural history of San Mateo County, California Near threatened animals Rigway's rail San Francisco Bay Taxa named by Robert Ridgway