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Literature Review

Bufo microscaphus californicus

USFWS: Endangered
CDFG: Species of Special Concern

Background

Distribution, Abundance and Trends. The arroyo toad is a federal Endangered species and a state Species of Special Concern. The arroyo toad is a California and Baja endemic. Historically it occurred from the upper Salinas River in San Luis Obispo County south along the coast to the Rio Santo Domingo system in Baja California, Mexico. There are records from six desert side drainages. The species has disappeared from 76% of its historic range as of 1994 (Jennings and Hayes 1994a). The northern, central and eastern portions of the range have lost all of their populations. It is currently known from only a few scattered localities within its historic range. About 40% of the known extant populations occur in areas owned or managed by the U.S. Forest Service (Brown 1993). The arroyo toad has highly specialized habitat requirements. Arroyo toad breeding sites are known to be streams of second to sixth order with overflow pools, depending somewhat on latitude (Sweet 1992, Griffin 1999). The streams and pools should be free of predatory fish. The adults breed in pools that have little woody vegetation along the margins and are shallow, sand or gravel based. The current velocity is generally low. The breeding pools occur near juvenile and adult habitat. This habitat is a shoreline or central bar and stable sandy terraces. The juveniles prefer areas that provide shelter either through drying algal mats or small damp refuges or depressions. The sandy terraces have an overstory of scattered shrubs and trees such as mulefat, California sycamore, Fremont cottonwood, or coast live oak. There is an absence of vegetation at ground level (Brown 1993; Jennings and Hayes 1994a). Arroyo toads have been found up to 1.08 km from water (Griffin 1999).

There is a 1992 record for this species from Whitewater Canyon. It is unknown if it is still extant, although the habitat is intact. Mark Jennings (pers. comm.) suggests that the only other likely sites in the Plan area would be Palm Canyon and Mission Creek. USFWS has suggested that Snow Creek could also provide appropriate habitat. The Whitewater population represents one of six desert localities of this more typically coastal area species. The current status and viability of the habitat locations for this species within the Plan area are unknown at this time. Surveys are needed to determine if the arroyo toad still occurs in Whitewater Canyon and if the species occurs at Snow Creek or Mission Creek. Potential habitat in Palm Canyon is on land owned by the Agua Caliente Band of Cahuilla Indians.

Threats and Limiting Factors. Arroyo toad breeding habitat is created and maintained by the fluctuating hydrological, geological, and ecological processes operating in riparian ecosystems and the adjacent uplands within a Mediterranean climate. These riparian/wash habitats as well as adjacent upland habitats are essential for the species' survival. Periodic and unpredictable flooding that reworks stream channels and channel sediments and alters pool location and form, coupled with upper terrace stabilization by vegetation, is required to keep a stream segment suitable for all life stages of the arroyo toad. There are many threats to this species throughout its range, all of which could potentially be a problem to the Whitewater population. Human activities that affect water quality, influence the timing and amount of non-flood flows or frequency and intensity of floods, affect riparian plant communities, or alter sedimentation dynamics can reduce or eliminate the suitability of stream channels for arroyo toad breeding habitat. The development and alteration of streamside gravel bars and terraces is probably the main factor in the lost of habitat (Jennings and Hayes 1994a). Degradation or loss of surrounding uplands reduces and eliminates foraging and overwintering habitat. This species is especially vulnerable to predation by exotic fishes and bullfrogs. Exotic plants can also adversely impact the habitat. The streamside bank and terrace habitat is popular for human uses such as camping, wading, ORV use, and suction dredge mining. Arroyo toads crossing or foraging on roads in the habitat area are also subject to mortality. Livestock grazing can affect arroyo toads directly and indirectly through impacts on habitat features.

Special Considerations. . Within the Plan area, other species of concern whose habitat overlaps with that of the arroyo toad include least Bell's vireo, yellow warbler, yellow-breasted chat, southwestern willow flycatcher, and summer tanager.