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Stanislaus River Report


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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept. of Fish and Game

Western Spadefoot Toad

Scaphiopus hammondi

California Department of Fish and Game "Species of Special Concern"


Life History

The western spadefoot toad ranges in size from 1.5 to 2.5 inches in length. Their coloration can be green, brown, yellow, or gray with irregular light stripes and random darker blotches. The skin of this toad is relatively smooth with scattered small tubercles, red or orange tipped in some individuals; the coloration of the belly is whitish. The body of the spadefoot toad is plump with short limbs, the eyes are large with vertical pupils, and the eardrum is apparent. The most distinguishing characteristic of this species is the prominent sharp-edged "spade" on each hind foot.

Spadefoot toads are strictly nocturnal; during the day and long dry periods they hide in deep, almost vertical burrows. Most of the year is spent in these underground burrows which are up to 36 inches deep (Stebbins 1972). During dry periods, the moist soil inside burrows provides water for absorption through the skin (Ruibal et al. 1969, Shoemaker et al. 1969).

These burrows are usually constructed by the toads using the spades on their hind feet, although some individuals use mammal burrows. On warm, moist nights during the summer they emerge to feed. Adult spadefoot toads consume insects, worms, and other terrestrial invertebrates. Other than the breeding season the adults do not move around much, but are sit-and-wait predators.

Most surface movements by adults are associated with rains or high humidities at night. Breeding usually occurs during the spring with the onset of the first heavy rains following warm days at which time large numbers can occasionally be seen. Within two days the females have finished laying their eggs which are laid in short, thick bands wound around the stems of water plants or on the upper surfaces of small submerged rocks. The eggs hatch in as little as one and one-half days.

Tadpoles usually reach metamorphosis in four to six weeks. The feeding tadpoles sometimes swim around in large aggregations creating whirlpools which suck up and concentrate plankton and organic material from the bottom of the pool (Bragg 1962, Halliday 1945) and then filter out food by passing water over their gills. Tadpoles are also carnivorous, consuming dead aquatic larvae of amphibians, including their own species (Bragg 1964). Recently metamorphosed juveniles seek refuge in the immediate vicinities of breeding ponds for up to several days after transformation. They hide in drying mud cracks, under boards, and other surface objects which can include decomposing cow dung (Weintraub 1980).

The western spadefoot is primarily a species of the lowlands, frequenting washes, floodplains of rivers, alluvial fans, playas, and alkali flats, but also ranges into the foothills and mountain valleys. It prefers areas of open vegetation and short grasses where the soil is sandy or gravelly (Stebbins 1985). It ranges throughout much of the Central Valley, coast ranges and foothills below 3000 foot. It is usually in high densities where it does occur, but is rapidly losing breeding ground to land development.

Findings and Conclusions

Agriculture, urban developments, and extensive grazing have degraded or eliminated freshwater habitat for this species.

Historically the spadefoot toad ranged throughout the Central Valley. In 1990 this species was observed northwest of Knights Ferry and in 1992 they were found approximately 13 miles southeast of Oakdale near Tulloch Reservoir (NDDB 1994). Surveys conducted for the SR-120 Oakdale Bypass Project found this species less than one mile south of the river and east of the Orange Blossom Bridge (BioSystems 1994).

The Stanislaus River backflows do not offer an adequate breeding environment due to high predator numbers and fluctuating stream flows. However, within the river corridor there may be seasonal pools in the foothill and canyon reaches of the study area. Projects which could affect the grassland and seasonal pools along the Stanislaus River could also possibly affect the spadefoot toad and therefore additional surveys would be necessary.