Degree of Threat: High
Comments: Most of the remaining range, including population strongholds in eastern Alameda and Contra Costa counties and areas south and west of Millerton Lake in Madera and Fresno counties, is imminently threatened by urban development, conversion of natural habitat to agriculture, introduction of exotic predatory animals (bullfrogs, crayfish, various fishes) that temporarily may occupy salamander breeding habitat, and/or other anthropogenic factors (e.g., rodent control programs, vehicular-related mortality). Reduced ground squirrel populations may reduce the availability of burrows, which are important habitat during the dry season. Use of pesticides for mosquito abatement may reduce food resources for salamanders. Introduction of non-native tiger salamanders may harm populations through hybridization and/or competition. Contaminated runoff from roads may adversely affect salamanders in breeding sites. Chytrid fungus (associated with decline of other amphibian species) has been identified in this species (Santa Clara County), but the infection was not reported as being associated with a die-off (Padgett-Flohr and Longcore 2005). Localities in the Diablo Range, inner Coast Ranges, and Sierra Nevada foothills are not significantly threatened at the present time, and there is a relatively large number of remaining breeding localities.
In Santa Barbara County, plans to convert remaining breeding areas from grazing to intensive agriculture are being developed and implemented (USFWS 2000). Five of the six existing habitat complexes supporting this population suffered moderate to severe levels of habitat destruction or degradation between 1996 and 2000 (USFWS 2000). See USFWS (2000) for further information on threats to the Santa Barbara County population.
Sonoma County population: Primary threat is continuing habitat destruction, degradation, and fragmentation. Reduction in the extent and amount of suitable water bodies, grasslands, and other suitable upland habitats likely has eliminated connectivity among most of the breeding sites, making recolonization of some sites following local extinction more difficult. In addition, habitat reduction lowers the quality of the remaining habitat, by reducing the amount of food, rodent burrows, and other resources (USFWS 2002). Plans to construct a residential development will result in the loss of one of the seven remaining breeding sites and severely impact and further isolate another two of the remaining breeding sites. Because these losses constitute an emergency posing a significant and imminent risk to the well-being of the Sonoma County Distinct Population Segment, USFWS (2002) found that emergency listing was necessary. Secondary threats exist from predation and competition from introduced exotic species; possible commercial overutilization; disease; hybridization with non-native salamanders; various chemical contaminants; road-crossing mortality; rodent control operations, and the species' small remaining population (USFWS 2003). The various primary and secondary threats are not currently being offset by existing Federal, State, or local regulatory mechanisms. The Sonoma County California tiger salamander also is vulnerable to chance environmental or demographic events, to which small populations are particularly vulnerable. The combination of its biology and specific habitat requirements makes the animal highly susceptible to random events, such as drought, disease, and other occurrences. Such events are not usually a concern until the number of breeding/estivation sites or geographic distribution become severely limited, as is the case with the Sonoma County California tiger salamander (USFWS 2003). Predation and competition by introduced or non-native species potentially affects all of the known Sonoma County California tiger salamander breeding sites (USFWS 2002). USFWS (2003) discussed hybridization with non-native tiger salamanders (A. tigrinum)--documented as occurring elsewhere in the range of A. californiense--as a potential threat to this population. See USFWS (2002, 2003) for further discussion of potential threats.