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).
Habitat and Ecology
This species usually occurs in or near quiet permanent water of streams, marshes, ponds, lakes, and other quiet bodies of water. In summer, frogs estivate in small mammal burrows, leaf litter, or other moist sites in or near (within a few hundred feet of) riparian areas (Rathbun et al. 1993, cited by USFWS 1994; USFWS 1996). Individuals may range far from water along riparian corridors and in damp thickets and forests. Breeding occurs in permanent or seasonal water of ponds, marshes, or quiet stream pools, sometimes in lakes (Fellers, in Jones et al. 2005); eggs often are attached to emergent vegetation, float at surface (Hayes and Miyamoto 1984).
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).
Total adult population size is unknown but undoubtedly exceeds 10,000. The species is still locally abundant in portions of the San Francisco Bay area and the central coast (USFWS 2000). Breeding sites in Marin County include several thousand adults (Fellers, in Lannoo 2005).
Over the long term, extent of occurrence, area of occupancy, number of subpopulations, and population size have undergone a major decline. The species has been extirpated from much of its former range in California (Hayes and Jennings 1988, Shaffer et al. 2004). Range has been reduced by 70% (USFWS 1996, 2000). Currently, area of occupancy, number of subpopulations, and population size probabaly are still declining, but the rate of decline is unknown.
Factors contributing to the decline 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 1998; USFWS 1994, 1996, 2000; Adams 1999, 2000; Lawler et al. 1999; Cook and Jennings 2001; Kiesecker, Blaustein and Miller 2001a; Cook 2002). An important threat is the loss of wetlands in the Willamette Valley (Oregon) and Puget Lowlands (Washington). Conversion of habitat to more permanent ponds is an important threat (as this allows breeding waters to be invaded by non-native predators).
Declines in the red-legged frog complex 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.
The U.S. Geological Survey has developed a conservation plan for this species, and about 1.7 million hectares were designated as critical habitat for it in California (USFWS 2001). A monitoring and conservation program needs to be implemented in the Mexican portion of the range, which does not include any protected areas.
Red List Status
Listed as Vulnerable in view of the small estimated area occupied by viable populations (estimated at less than 500 sq km; total occupied area may be substantially larger), severely fragmented distribution, and continuing decline in populations and area and quality of habitat. This species has undergone a major, long-term decline. Most of the decline occurred more than 10 years or three generations ago.
Significant morphological and behavioral differences between Rana draytonii and R. aurora suggest that they represent two species in secondary contact (Hayes and Krempels 1986, cited by USFWS 1994). Shaffer et al. (2004) presented genetic evidence supporting the recognition of Rana aurora and R. draytonii as distinct species.
Geoffrey Hammerson 2008. Rana draytonii. The IUCN Red List of Threatened Species 2008: e.T136113A4240307. http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T136113A4240307.en .Downloaded on 18 February 2019