Description A medium sized frog. Gray, brown, reddish or olive above; sometimes plain-colored but more often spotted and mottled with dusky hues. Colors usually harmonize with the prevailing color of rocks and soil and can be quite cryptic. Yellow extends from the underside of the hind legs onto the lower abdomen. Snout with a triangular, usually buff-colored patch from its tip to a line connecting the eyelids. Throat and chest often dark-spotted. Skin, including the eardrums, granular. Indistinct dorsolateral folds. Inconspicuous vocal sac on each side of throat, in front of the forelimbs (Stebbins 1985).
Range: West of crest of Cascade Mountains, Oregon, south in coastal mountains of California, to San Gabriel River, Los Angeles Co.; Sierra Nevada foothills to about 1830 m (near McKessick Peak, Plumas Co.); San Pedro Martir (lower end of La Grulla meadow, 2040 m), Baja CA. Isolated populations in Elizabeth Lake Canyon and San Gabriel River drainage (near Camp Rincon), Los Angeles Co,; Sutter Buttes, Butte Co., CA (Stebbins 1985). The Camp Rincon population is perhaps now extinct (Lind et. al. 1996). A single record 8 km north of Lodi, San Joaquin Co., CA, perhaps a stray from the Sierra Nevada foothills (Lind et. al. 1996).
Habitat: Streams and rivers in woodland, chaparral, and forest (Stebbins 1985). Found near water, especially near riffles where there are rocks, rocky subtrate, and sunny banks. When frightened, these frogs will dive to the bottom and takes refuge among stones or vegetation, remaining still (Stebbins 1985).
Life History, Abundance, Activity, and Special Behaviors Breeds from the latter part of March to the first of May. Females oviposit eggs in shallow water toward the margin of streams, attached to sides of stones in the stream bed. Eggs are laid in clusters (Wright and Wright 1949).
Voice is seldom heard. It is a guttural, grating sound either at one pitch or with rising inflection, a single croak lasting 1/2-3/4 of a second. Four or five croaks may be given in rapid series followed by a rattling sound, with the entire sequence lasting about 2.5 seconds (Stebbins 1985).
Trends and Threats This is a California species of special concern and a candidate for Federal Listing (Lind et. al. 1996). Notable declines in southern California and the west slope drainages of the Sierra Nevada and southern Cascade Mountains (Lind et. al. 1996).
Threats: Construction of dams. Predation by bullfrogs (Rana catesbeiana), a non-native species (Lind et. al. 1996).
Throughout much of the Pacific Coast and Sierra Nevada drainages, the once abundant Foothill Yellow-legged frog has been disappearing, mainly due to habitat destruction, water diversion and pollution. In 2005, only 30 California sites had populations of 20 or more adults, including in the heart of their range in California’s north coast where the frogs have lost a quarter of their historic sites. On December 14, 2016, the Center for Biological Diversity (CBD) formally petitioned the US Fish And Wildlife Service to list the Foothill Yellow-legged frog as a threatened species under the California Endangered Species Act. This joins the the CBD’s 2012 petition for federal listing under the Endangered Species Act. Hopefully the state can act to protect this frog faster than the federal officials, who are expected to make a decision in 2020, none too soon for a disappearing species.
Possible reasons for amphibian decline
General habitat alteration and loss Urbanization Dams changing river flow and/or covering habitat Long-distance pesticides, toxins, and pollutants Predators (natural or introduced)
Comments Male Rana boylii establishing its territory.
Video submitted by Pierre Fidenci.
Male and gravid female Rana boylii during mating season.
Videos submitted by Pierre Fidenci.
This species was featured as News of the Week on 11 April 2022:
Amphibians dwelling in Mediterranean climates are adapted to hot, dry summers and cool, wet winters, but climate change is intensifying the cycle of droughts and floods in these habitats. How do riverine frogs persist when surface flow becomes intermittent? Kupferberg et al. (2021) investigated this by mapping frog distribution in habitat mosaics created by seasonal drying of stream channels in two San Francisco Bay Area watersheds (California, USA). They monitored populations of the Foothill Yellow-legged Frog (Rana boylii), an imperiled species indigenous to rivers and streams of California and Oregon, and found that although water may not last long enough after spring egg-laying for tadpoles to reach metamorphosis during droughts, the drying appears to allow co-existence with the invasive North American Bullfrog (Rana (Aquarana) catesbeiana). Bullfrogs can tolerate the fungal disease, chytridiomycosis, while Rana boylii is vulnerable to its lethal effects. In the autumn when frogs concentrate at remnant pools and cold snaps occur, conditions are ripe for transmission of pathogens and juvenile frogs succumb to disease. Despite local die-offs and episodes of poor recruitment, more than two decades of monitoring revealed that R. boylii populations can rebound after wetter winters that create sufficiently long hydroperiods for tadpoles to reach metamorphosis. (Written by Sarah Kupferberg)
This species was featured as News of the Week on 13 August 2018:
Rana boylii, the Foothill Yellow-legged Frog of Oregon and California, is a declining species considered to function as a "sentinel" for assessing ecological health of stream ecosystems. Its phylogeography was studied using a large dataset (RADseq) in a landscape genomics approach (McCartney-Melstad et al. 2018). The five primary clades are extremely differentiated, with about half of the range occupied by a rather genetically uniform population. The peripheral clades are hierarchically substructured and should be treated as separate management units for conservation purposes (rather than previous watershed units). The species is apparently extinct in southern California and the southwestern-most peripheral clade in Monterey County is near extinct and shows the lowest genetic diversity. This study finds Foothill Yellow-legged Frog to be one of the most genetically diverse frog species and points the way for improved species recovery targets (Written by David B. Wake).
This species was featured as News of the Week on 25 February 2013:
The effects of dams are well documented on fish species (e.g., salmon) but less is known about how dams affect amphibians. A paper in Conservation Biology shows that dams negatively affect river-breeding frogs in California, such as Rana boylii. Kupferberg et al uses 20 years of frog breeding data from regulated (dammed) and unregulated (un-dammed) rivers to show that by altering the flow regime, dams are causing higher egg and tadpole mortality. Dammed rivers that add artificial peak flows in summer months, for example for boating recreation, have the worst impact on native amphibians. (Written by Vance Vredenburg)
Kupferberg, S.J. (1996). ''Hydrologic and geomorphic factors Affecting conservation of a river-breeding frog (Rana boylii).'' Ecological Applications, 6(4), 1332-1344.
Lind, A. J., Welsh, Jr., H. H., and Wilson, R. A. (1996). ''The effects of a dam on breeding habitat and egg survival of the foothill yellow-legged frog (Rana boylii) in northwestern California.'' Herpetological Review, 27(2), 62-67.
Miller, J. (2016). ''Petition Filed for State Endangered Species Act Protection for Rare California Frog.'' Center for Biological Diversity. http://www.biologicaldiversity.org/news/press_releases/2016/foothill-yellow-legged-frog-12-14-2016.php Downloaded on 9 January 2017
Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
Wright, A. H. and Wright, A. A. (1949). Handbook of Frogs and Toads of the United States and Canada. Comstock Publishing Company, Inc., Ithaca, New York.