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Arroyo Toad, by Bradford Hollingsworth Bufo californicus
Arroyo Toad

BUFONIDAE

Bufo from the Latin word bufonis which means toad and californicus is a Latinized proper name, in reference to its distribution in southern California and northern Baja California.

Description

In 1998, a research scientist, Erik Gergus, reviewed the evolutionary relationships of the complex of toads assigned to the name Bufo microscaphus. It was determined that each of the three recognized subspecies should be elevated to full species. Bufo microscaphus californicus became Bufo californicus. This species was originally described by Charles L. Camp in 1915.

The Arroyo Toad is a relatively small (2-3 inches snout-vent length) frog. Its coloration ranges from olive green or gray to light brown. It can be distinguished from other toads by non-paired, symmetrical dorsal blotches, bicolored parotid glands that are dark posteriorly and light anteriorly as well as a light spot on the sacral humps. A prominent white "v-shaped" stripe crosses the top of the head between the eyes. It lacks a middorsal stripe. The belly is buff-white and often lacks spots. Locomotion is generally in the form of hopping as opposed to walking or taking large jumps.

Tadpoles are difficult to distinguish from those of the Western Toad immediately after hatching, but changes in coloration, size and shape are apparent several weeks later. At hatching, the tadpoles of both species are small and black. Later, the Arroyo Toad tadpoles become tan as opposed to the darker color of the Western Toad larvae. The tadpoles are also more fusiform in shape as opposed to the globose shape of the Western Toad tadpoles. Western Toad tadpoles are communal, occurring in aggregates whereas Arroyo Toad tadpoles distribute themselves evenly within the pools they inhabit. After metamorphosis, toadlets appear as miniature adults with the exception of having yellow spots.

Tadpoles, modified from Sweet (1992)
Tadpole drawing modified from Sweet (1992)

Range and Habitat

The Arroyo Toad inhabits coastal southern California from Salinas River Basin in Monterey and San Luis Obispo Counties to Arroyo San Simón in northern Baja California, México. It has been reported from Arroyo Grande near El Rosario based on a call; however this needs further confirmation.

This toad prefers riparian habitats with sandy streambeds with cottonwood, sycamore, and willow trees. Some populations occur in streams within coniferous forests. The stream setting usually has adjacent shallow pools where the toad may sit in the water while partially exposed above.

Natural History

These toads are most active during late winter and early spring after seasonal rains. Early in their activity season, toads forage to prepare for breeding. Later, males disperse along the margins of streams and initiate calling to attract females. Little is known about their habits outside of their breeding season. It is known that toads will disperse as much as a kilometer from their stream sites in the nonbreeding season.

Life History: This toad is chiefly nocturnal. Several life history characteristics make it unique among most toads: eggs are laid at calling sites of males, tadpoles are cryptically colored, non-toxic, and solitary, and juveniles disperse after the wet season ends.

Arroyo Toad, by Bradford Hollingsworth

Breeding: Breeding is accomplished through the process of amplexus where the male grabs the female from behind. After a female chooses a calling male, she will be grasped beneath the armpits by the male. Through this stimulation, the female will lay her strings of eggs into the water. It may take a few days before the female is ready to lay her eggs, so the male has to hang on until she does. At the same time when the eggs are laid, the male will fertilize them. The entire process occurs in the open water. Eggs are laid from March to July, but this depends on sufficient weather conditions and annual rainfall. Breeding season maybe extended in exceptionally wet years. Eggs are small, dark, and laid in strings along the edges of pools with mild current velocities. Tadpoles develop over an extended period of 65-85 days. The lengthy larval period makes them extremely susceptible to mortality during this time.

Voice: The Arroyo Toad call is a long trill lasting 4-10 seconds that is roughly similar to some insect calls.

Predators: Tadpoles are eaten by water bugs, garter snakes, bullfrogs, and a number of fish species. Toadlets and adults are attacked by killdeer, herons, garter snakes, and bullfrogs. It is also reasonable to conclude that turtles, raccoons, opossums, and ravens would prey upon them.

Conservation Status

Federally listed as an endangered species, the Arroyo Toad is fully protected by the U.S. Fish and Wildlife Service and California Department of Fish and Game. The Arroyo Toad was listed as an endangered species on December 16, 1994 (U.S. Fish and Wildlife Service, 1994). The main cause of decline for this species in the United States is the loss of habitat. This loss has been attributed to urbanization, agriculture, and dam construction within the toad's preferred habitat (U.S. Fish and Wildlife Service, 1999). Little is known of the status of populations from northwestern Baja California.

Suggested Reading

U.S. Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants; determination of endangered status for the arroyo southwestern toad. Federal Register 59(241):64589 - 64866.

U.S. Fish and Wildlife Service. 1999. Arroyo southwestern toad (Bufo microscaphus californicus) recovery plan. U.S. Fish and Wildlife Service, Portland, Oregon. vi + 119 pp.

Sweet, S. S. 1992. Ecology and status of the arroyo toad (Bufo microscaphus californicus) on the Los Padres National Forest of southern California, with management recommendations. Report to United States Department of Agriculture, Forest Service, Los Padres National Forest, Goleta, California. ii + 198 pp.

Sweet, S. S. 1993. Second report on the biology and status of the arroyo toad (Bufo microscaphus californicus) on the Los Padres National Forest of southern California. Report to United States Department of Agriculture, Forest Service, Los Padres National Forest, Goleta, California. ii + 73 pp.

Gergus, E. W. A. 1998. Systematics of the Bufo microscaphus complex: allozyme evidence. Herpetologica 54(3):317 - 325.


Text by Brad Hollingsworth, Kim Gray-Lovich, and Rob Lovich.
Photos by Bradford Hollingsworth.
Tadpole drawing modified from Sweet (1992).

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