Rana draytonii

Genetic evidence supporting the recognition of Rana aurora and R. draytonii as distinct species is presented by Hayes and Miyamoto (1984), Shaffer et al. (2004), Conlon et al. (2006), and Pauly et al. (2008).

Restricted mostly to California, where populations have declined greatly due to habitat loss and degradation, past overexploitation, and introduced species; species continues to be threatened by habitat degradation and exotic species.

Native historical range extended from southern Mendocino County in northwestern California south (primarily west of the Cascade-Sierra crest) to northwestern Baja California (Shaffer et al. 2004). Historical populations on the floor of the Central Valley may not have persisted due to extensive natural flooding (Fellers, in Lannoo 2005). Range is now much reduced in the Sierra Nevada and in southern California, but the species is still present throughout much of its former range in the central California coast range (Fellers, in Lannoo 2005). This species has been introduced in a few places in Nevada, but the current status of those populations is uncertain (A. Cook, cited by Fellers, in Lannoo 2005). Rana draytonii is still present in Baja California, Mexico (USFWS 2000, Grismer 2002, Shaffer et al. 2004). Elevational range extended from sea level to about 1,500 meters (5,000 feet); usually below 1,200 meters (3,935 feet).

Number of distinct occurrences (subpopulations) is unknown but probably is at least several dozen. According to USFWS (2000), the species occurs in about 238 streams or drainages.

In the mid-1990s, most of the occupied habitat was in Monterey, San Luis Obispo, and Santa Barbara counties; the species occurred in only 5 sites south of the Tehachapi Mountains (80+ historic sites) (USFWS 1996) Aggregations including more than 350 adults were known only from Pescadero Marsh Natural Preserve in coastal San Mateo County, Point Reyes National Seashore in Marin County, and Rancho San Carlos in Monterey County (USFWS 1996). More than 120 breeding sites exist in Marin County (Fellers, in Lannoo 2005).

In California, south of Los Angeles, a single population is known from the Santa Rosa Plateau in Riverside County (Shaffer et al. 2004). Only two populations are known to exist south of Santa Barabra (Fellers, in Lannoo 2005).

In the Sierra Nevada, Rana draytonii is now represented by only about a half dozen populations, only one of which is known to have more than 10 breeding adults (Shaffer et al. 2004).

Factors contributing to local declines include wetland destruction and degradation/fragmentation, urbanization, residential development, reservoir construction, stream channelization, livestock grazing of riparian vegetation, off-road vehicle activity, drought, overharvesting, and exotic fishes (bass, mosquitofish) and possibly bullfrogs (Kiesecker and Blaustein 1988, 1998; USFWS 1994, 1996, 2000; Adams 1999, 2000; Lawler et al. 1999; Cook and Jennings 2001; Kiesecker, Blaustein and Miller 2001a; Cook 2002). Conversion of habitat to more permanent ponds is an important threat (as this allows breeding waters to be invaded by non-native predators). Habitat characteristics and good leaping ability may render Rana aurora/draytonii less vulnerable to bullfrog predation than is Rana pretiosa (Pearl et al. 2004). McAllister and Leonard (in Jones et al. 2005) noted that in many areas red-legged frogs coexist with bullfrogs.

Declines in the red-legged frog complex (including Rana draytonii) also have been attributed to global warming, UV-B radiation (Belden and Blaustein 2002), airborne contaminants (pesticide drift), and disease (see Davidson et al. 2001). Davidson et al. (2002) found support for the negative impact of wind-borne agrochemicals and weaker evidence for the widespread impact of habitat destruction and UV-B radiation; evidence did not support the hypothesis that declines have been caused by climate change.