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Jennings and Hays Species of Special Concern /! 94
<br /> /N 6Q&1,c_6A1_A11,4
<br /> 6 AME WESTERN SPADEFOOT
<br /> Scaphiopus hamnwndii Baird 1859
<br /> l9 q q Description: A moderate-sized (37.0-62.0 mm SUL) greenish, grayish, or brownish
<br /> toad irregularly marked with dark orange-or reddish-tipped tubercles; having faint
<br /> hourglass markings on the back consisting of four irregular, light-colored stripes; and
<br /> possessing a distinctive, black, cornified, teardrop-shaped spade on each hindfoot (Storer
<br /> 1925, Stebbins 1985). Hindlimbs are short, and undersurfaces are cream to dirty white.
<br /> Constricted pupils have a vertical, fusiform shape, and the iris is pale gold because of a
<br /> prominent reticulum of gold iridophores on a brown ground color (pers. observ.).
<br /> Taxonomic Remarks: For many years, Scaphiopus hammondii were regarded as
<br /> having a broad geographic range from California to western Texas and Oklahoma with a
<br /> hiatus across the Colorado River(Storer 1925; Stebbins 1951, 1966). However, Brown
<br /> (1976) identified morphological, vocalization, and reproductive differences between eastern
<br /> (Arizona eastward) and western (California) populations,justifying species recognition for
<br /> each. Since the work of Brown (1976), the name S. hairmiondii has been applied
<br /> exclusively to California populations. Genetic variation across the range of S. hammondii
<br /> has not been studied.
<br /> Distribution: This near endemic to California ranges from the vicinity of Redding,
<br /> Shasta County, southward into northwestern Baja California, Mexico (Stebbins 1985). Its
<br /> known elevational range extends from near sea level to 1363 in (Zeiner et al. 1988). In
<br /> California, the known range of S. hammondii is entirely west of the Sierran-desert range
<br /> axis (Myers 1944; Figure 26).
<br /> Life History: Scaphiopus hammondii is almost completely terrestrial, entering water
<br /> only to breed (see Dimmitt and Ruibal 1980a). Western spadefoots become surface active
<br /> following relatively warm (>_ 10.0-12.8°C)rains in late winter-spring and fall,emerging
<br /> from burrows in loose soil to a depth of at least 1 in (Stebbins 1972; A. McCready,pers.
<br /> comm.),but surface activity may occur in any month between October and April if enough
<br /> rain has fallen (Morey and Guinn 1992; S. Morey, pers. comm.). Amount of rain may be
<br /> a better predictor of surface activity than temperature(S.Morey, pers. comm.), but the cue
<br /> or combination of cues that induces emergence in S. hammondii remains poorly
<br /> understood. Western spadefoots can form large (> 1000 individuals),highly vocal,
<br /> breeding aggregations (pers. observ.), although choruses are oftenmuch smaller(A.
<br /> McCready,pers. comm.). Females deposit eggs in irregular small cylindrical clusters of
<br /> 10-42 attached to plant stems or pieces of detritus in temporary rain pools, or sometimes
<br /> pools in ephemeral streamcourses (Storer 1925; Stebbins 1985; pers. observ.). The critical
<br /> thermal minimum of early embryos is 9°C (Brown 1967), so oviposition does not occur
<br /> until temperatures permit some warming of rainpools in late winter (pers. observ.).
<br /> Depending on the temperature regime and annual rainfall,oviposition may occur between
<br /> late February. and late May (Storer 1925, Burgess 1950, Feaver 1971, Stebbins 1985).
<br /> Eggs hatch in 0.6-6 days, depending on temperature(Brown 1967), and larval
<br /> development can be completed in 3-11 weeks (Burgess 1950; Feaver 1971; S. Morey and
<br /> K. Baldwin, pers. comm.), the variation depending on food resources and temperature.
<br /> No data are available to indicate how long S.hammondii needs to reach sexual maturity,
<br /> but considering the relatively long period of subterranean dormancy (8-9 months; pers.
<br /> observ.), individuals probably require at least 2 years to mature. Adults have a moderate
<br /> stomach capacity (they can eat roughly 11% of their body mass at a single feeding; Dimmitt
<br /> and Ruibal 1980b) and can probably acquire enough energy to survive the long annual
<br /> dormancy interval in a few weeks. Known food items taken include crickets
<br /> (Gryllacrididae), butterflies, beetles, flies, ants, and earthworms (Morey and Gullin 1992).
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