Taxonomic notes: Section empty

This species formerly ranged from San Luis Obispo County, California, USA, south to north-western Baja California in Mexico; see Gergus, Sullivan and Malmos 1997 for southernmost record. It is now apparently extirpated in San Luis Obispo County; populations persist in headwater areas of streams in Santa Barbara, Ventura, Los Angeles, Riverside, and San Diego counties; recent sightings of scattered individuals have been reported from Orange, San Bernardino, and southern Imperial counties (USFWS 1994). The majority of the remaining populations in Santa Barbara and Ventura counties are in Los Padres National Forest (five viable populations); Sespe Creek in Ventura County has the largest known population. Other populations occur in the Sisquoc, Santa Ynez, and upper and lower Piru drainages (USFWS 1994). It also occurs in San Diego County along the Santa Margarita, Guejito, Sweetwater, Vallecito, San Luis Rey, Santa Ysabel, Witch, Cottonwood, Temescal, Agua Caliente, Santa Maria, Lusardi, Pine Valley, Noble, Kitchen, Long Potrero, Upper San Diego, San Vicente, and Morena drainages; populations in the Temescal, Agua Caliente, Pine Valley, and Cottonwood drainages may be considered viable (USFWS 1994). It was recently recorded in Whitewater Canyon in Riverside County (Patten and Myers, 1992, Herpetol. Rev. 23:122). Recent surveys located very small populations in four creeks in south-western Riverside County (Temecula, Arroyo Seco, San Mateo, and Tenaja creeks) (USFWS 1994). The single recent record in San Bernardino County is from Deep Creek in the San Bernardino National Forest. It is also still extant in north-western Baja California.

This species inhabits washes, streams, and arroyos, and adjacent uplands (in desert and shrubland). It is also found on sandy banks in riparian woodlands (willow, cottonwood, sycamore, and/or coast live oak) in California. It is also found along rivers that have shallow gravelly pools adjacent to sandy terraces (USFWS 1993). Adults obtain shelter by burrowing into sandy soil. It lays eggs among gravel, leaves, or sticks, or on mud or clean sand, at the bottom of shallow quiet waters of streams or shallow ponds, in areas with little or no emergent vegetation. Newly metamorphosed individuals remain near pools for up to several weeks (until the pools dry up).

The total estimated breeding population is less than 3,000 individuals (USFWS, Federal Register, 6 May 1998). Only six of the 22 extant populations south of Ventura are known to contain more than a dozen adults (USFWS 1994). It has been extirpated from an estimated 75% of its former range in the USA (Sweet, in USFWS 1993). Reproductive success has been poor in recent years (USFWS 1993). There is very little recent information on the trends in this species in Mexico. It occurs in at least a couple dozen sites, but viable populations may remain in only five drainages (USFWS 1993). It is known in California from 22 river basins in nine counties (USFWS 1999). Since 1990 there has been a decrease of about 65% on its populations in the USA (USFWS, 1999).

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Threats include habitat degradation (mainly through urbanization, dam construction and ill-timed water releases, agriculture, road construction, off-road vehicle use, overgrazing, and mining activities, and also via drought and wildfires) (Lovich, et al, 2009), recreational use of habitat (which causes habitat degradation and direct mortality), predation by introduced fishes and bullfrogs (Rana catesbeiana), and small population sizes (see USFWS 1993 and 1994 for further details).

• 2.1.4 Scale Unknown/Unrecorded
• 7.1.1 Increase in fire frequency/intensity
• 1.1 Housing & urban areas
• 1.3 Tourism & recreation areas
• 4.1 Roads & railroads
• 2.3.4 Scale Unknown/Unrecorded
• 7.2.11 Dams (size unknown)
• 1.2 Commercial & industrial areas
• 11.2 Droughts
• 6.1 Recreational activities
• 8.1.1 Unspecified species
• 3.2 Mining & quarrying

USFWS (2001) designated as critical habitat approximately 182,360 acres in 22 units in Monterey, Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside, Orange, and San Diego counties. Critical habitat includes stream and river courses, riparian areas, and adjacent terrace and upland habitats. It does not include existing structures or other developed areas. See recovery plan (USFWS 1999). In Mexico this species is found within San Pedro Martir National Park.

• 2.1 Site/area management
• 2.3 Habitat & natural process restoration
• 3.2 Species recovery
• 4.3 Awareness & communications
• 1.1 Site/area protection

Listed as Endangered because of a serious population decline, estimated to be more than 50% over the last ten years, inferred from observed reduction in the extent and quality of its habitat, in the number of locations and number of mature individuals, and in the area of occupancy.

• Behler, J.L. and King, F.W. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. New York.
• Blackburn, L., Nanjappa, P. and Lannoo, M.J. 2001. An Atlas of the Distribution of U.S. Amphibians. Ball State University, Muncie, IN, USA.
• Collins, J.T. 1991. Viewpoint: a new taxonomic arrangement for some North American amphibians and reptiles. SSAR Herpetological Review: 42-43.
• Gergus, E.W.A. 1998. Systematics of the Bufo microscaphus complex: allozyme evidence. Herpetologica: 317-325.
• Gergus, E.W.A., Grismer, L.L., and Beaman, K. 1997. Geographic distribution: Bufo californicus. Herpetological Review: 47.
• Gergus, E.W.A., Sullivan, B.K. and Malmos, K.B. 1997. Bufo microscaphus complex call variation: species boundaries and mate recognition. Ethology: 1-11.
• Price, A.H. and Sullivan, B.K. 1988. Bufo microscaphus. Catalogue of American Amphibians and Reptiles: 1-3.
• Stebbins, R.C. 1954. Amphibians and Reptiles of Western North America. McGraw-Hill Book Company, New York.
• Stebbins, R.C. 1972. California Amphibians and Reptiles. University of California Press, Berkeley, California.
• Stebbins, R.C. 1985. A Field Guide to Western Reptiles and Amphibians. Second Edition. Houghton Mifflin Company, Boston, Massachusetts.
• Sullivan, B.K. 1992. Calling behavior of the southwestern toad (Bufo microscaphus). Herpetologica: 383-389.
• U.S. Fish and Wildlife Service. 1993. Proposed endangered status for the arroyo southwestern toad. Federal Register (3 August 1993): 41231-41233.
• U.S. Fish and Wildlife Service. 1994. Determination of endangered status for the arroyo southwestern toad. Federal Register (16 December 1994): 64859-6486.
• U.S. Fish and Wildlife Service. 1999. Arroyo southwestern toad (Bufo microscaphus californicus) recovery plan. Portland, Oregon.
• U.S. Fish and Wildlife Service. 2000. Proposed designation of critical habitat for the arroyo southwestern toad. Federal Register (8 June 2000): 36512-3654.
• U.S. Fish and Wildlife Service. 2001. Final designation of critical habitat for the arroyo toad. Federal Register (12 February 2001): 9414-9474.