- Baird, 1854
Foothill Yellow-legged Frog
Taxonomic Status: Accepted
Related ITIS Name(s):
Rana boylii Baird, 1854 (TSN 173449)
Spanish Common Names: Rana Pata Amarilla
Unique Identifier: ELEMENT_GLOBAL.2.102584
Element Code: AAABH01050
Informal Taxonomy: Animals, Vertebrates
- Frogs and Toads
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference: Frost, D. R. 1985. Amphibian species of the world. A taxonomic and geographical reference. Allen Press, Inc., and The Association of Systematics Collections, Lawrence, Kansas. v + 732 pp.
Concept Reference Code: B85FRO01HQUS
Name Used in Concept Reference: Rana boylii
Taxonomic Comments: MtDNA data suggest that R. aurora, R. cascadae, and R. muscosa form a clade within the R. boylii species group (Macey et al. 2001).
Global Status: G3
Global Status Last Reviewed: 01Sep2013
Global Status Last Changed: 15Nov2001
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G3 - Vulnerable
Reasons: Occurs in California and western Oregon; substantial ongoing decline, apparently due to habitat alteration (especially that caused by dams), impacts of airborne agrochemicals, and/or effects of exotic species, and because recolonization abilities may be greatly restricted by local extirpation patterns.
Nation: United States
National Status: N3
U.S. & Canada State/Province Status
California (S3), Oregon (S2S3)
IUCN Red List Category: NT - Near threatened
NatureServe Global Conservation Status Factors
Range Extent: 20,000-200,000 square km (about 8000-80,000 square miles)
Range Extent Comments: Range includes Pacific drainages from the upper reaches of the Willamette River system, Oregon (west of the Cascades crest), south to the upper San Gabriel River, Los Angeles County, California, including the coast ranges and Sierra Nevada foothills in the United States (Stebbins 2003). The species occurred at least formerly in a disjunct location in northern Baja California: two specimens (identified by R. C. Stebbins and R. G. Zwiefel) were collected in 1965 at an elevation of 2,040 meters at the lower end of La Grulla Meadow, Sierra San Pedro Martir, Baja California, Mexico (Loomis 1965); subsequent searches have not detected the species in that area (Grismer 2002, Stebbins 2003). The species apparently has disappeared from portions of its historical range, especially in southern California (see Hayes and Jennings 1988). Extant R. boylii populations are not evenly distributed in California; in the Pacific Northwest, 40 percent of the streams support populations, whereas that number drops to 30 percent in the Cascade Mountains (north of the Sierra Nevada), 30 percent in the south coast range (south of San Francisco), and 12 percent in the Sierra Nevada foothills (Fellers 2005). Elevational range extends from sea level to around 2,130 meters.
Number of Occurrences: 81 - 300
Number of Occurrences Comments: This species is represented by a large number of extant occurrences (subpopulations). It has been extensively searched for and commonly found in much of the northern half of the range. Since 1993, it has been found at more than 200 sites in California (Fellers 2005).
Population Size: 2500 - 100,000 individuals
Population Size Comments: Total adult population size is unknown but presumably exceeds 2,500. However, Fellers (2005) found that only 30 of the 213 sites in California with foothill yellow-legged frogs had populations estimated to be 20 or more adult frogs (Fellers 2005). The largest populations in California are in the north coast range where the estimated number of adult frogs exceeded 100 at six sites, and an additional nine populations had more than 50 adult frogs (Fellers 2005).
Number of Occurrences with Good Viability/Integrity: Some (13-40)
Viability/Integrity Comments: Only a small percentage of known occurrences exhibit good viability (see population size comments).
Overall Threat Impact: High
Overall Threat Impact Comments: Major threats include habitat loss and fragmentation and alteration of natural flow regimes as a result of dam construction (http://www.fs.fed.us/psw/topics/wildlife/herp/rana_boylii/), introduced incompatible aquatic animals, aerial drift of pesticides, riverine and riparian impacts of non-selective logging practices, and other habitat degradation and disturbance caused by livestock grazing and in-stream mining. Climate change presumably will have negative effects on this species if it results in increased stream dessication and reduced availability of suitable habitat.
On the main stem of the Trinity River, northern California, unnatural flow regimes and loss of habitat caused by dam construction are the greatest threats (Ashton et al. 1997). Potential breeding habitat was reduced by 94 percent after dam construction (Lind et al. 1996). Controlled flows allowed encroachment of riparian vegetation and retarded cobble/gravel bar formation. Since dam construction water releases have been reduced to 10-30 percent of pre-dam flows, based on both total yearly volume and magnitude of periodic high flows (Lind et al. 1996). High flow releases from dams in late spring sometimes result in scouring of egg masses, whereas receding high flows, if poorly timed, can leave egg masses "high and dry" (Lind et al. 1996). Source: Ashton et al. (1997).
Adults, larvae, and/or eggs are vulnerable to an array of non-native predators such as predatory fishes, bullfrogs, and crayfish (Lind et al. 1996, Kupferberg 1996, Ashton et al. 1997, Lind et al. 2003, Fellers 2005, Paoletti et al. 2011), but the population effects of these species and of potential non-native competitors are not well known. Dam-controlled flows and lack of winter flooding may result in stable pool areas with established aquatic vegetation (Lind et al. 1996, Kupferberg 1996), and this may increase suitable habitat for exotic species such as bullfrogs (Ashton et al. 1997). Decreased flows may force frogs into permanent pools where they are more susceptible to predation (Hayes and Jennings 1988). Kupferberg (UC Berkeley) found that bullfrog larvae perturbed aquatic community structure and exerted detrimental effects on Rana boylii populations in northern California but had only a slight impact on Pseudacris regilla (Froglog, September 1993). Interspecific matings between male R. boylii and female bullfrogs have been observed; these interactions with non-native bullfrogs might reduce the reproductive output of R. boylii (Lind et al. 2003).
Logging and erosion from road cuts have resulted in periodically high levels of stream siltation in some areas of northern California (Ashton et al. 1997). High levels of silt may inhibit the attachment of the egg mass to the substrate (Ashton et al. 1997). Excessive accumulation of silt on the egg masses may have adverse effects on embryo development (Jennings and Hayes 1994). Silt also reduces the interstitial spaces available for use by tadpoles, reduces algal growth on which the tadpoles feed (Power 1990), and can have a significant negative impact on adult frog food resources (e.g., aquatic macro-invertebrates; Petts 1984) (source: Ashton et al. 1997).
In the Sierra Nevada foothills of California, air-borne pesticides (that move east on the prevailing winds blowing across the highly agriculturalized Central Valley) are likely to be the primary threat (LeNoir et al. 1999; Sparling et al. 2001; Fellers 2005, Sparling and Fellers 2007). Davidson et al. (2002) found evidence that airborne agrochemicals have played a significant role in the decline; habitat destruction, climate change, and UV-B radiation appeared to be contributing factors in the decline of this species.
Ashton et al. (1997) mentioned the potential for spills of toxic materials into streams along roads along the Trinity River in northern California. Bury (1972) found that spilled diesel fuel had negative impacts on R. boylii tadpoles and partially transformed individuals but apparently little impact on adults.
Chytrid fungus has been found in this species, but its population effects are unknown (Fellers 2005). In laboratory experiments, Davidson et al. (2007) found that chytrid infection reduced growth of newly metamorphosed Rana boylii by approximately one-half.and that exposure to the pesticide carbaryl may increase susceptibility to chytrid infection.
Recolonization abilities may be greatly restricted by local extirpation patterns. For example, dams eliminate habitat and cause local extirpations, and they also interfere with normal dispersal and movements (Fellers 2005).
Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Trend over the past 10 years or three generations is uncertain, but probably the area of occupancy, number of subpopulations, population size, and habitat quality have declined.
Long-term Trend: Decline of 30-70%
Long-term Trend Comments: This frog is still common along the north coast of California (Fellers 2005). It still occurs in significant numbers in some coastal drainages in the Coast Ranges north of the Salinas River (Ashton et al. 1997). Fellers (1994) reported healthy, reproducing populations throughout suitable habitat in the Diablo Range in Alameda, western Stanislaus, Santa Clara, San Benito, and western Fresno counties.
A large decline has occurred in southern California (Sweet 1983, Jennings and Hayes 1994); the species is probably extirpated from the Tehacahapi Mountains south, it is still present but nowhere abundant in coastal California from Monterey County southward to northwestern San Luis Obispo County. Severe declines have occurred in central California (Drost and Fellers 1996). In view of these trends, Jennings and Hayes (1994) recommended endangered status in southern and central California south of the Salinas River, Monterey County, and threatened status in the "west slope drainages of the Sierra Nevada and southern Cascade Mountains east of the Sacramento-San Joaquin River axis."
The species formerly was regarded as at least locally abundant in southwestern Oregon (Fitch 1936, 1938), but now it is rare or absent through the entire western half of the Oregon range (Fellers 2005). This frog has disappeared from more than 50 percent of historical locations in Oregon and is presumed extirpated from most of the northern and far eastern portions of the range in Oregon (Hayes et al., in Jones et al. 2005).
Intrinsic Vulnerability: Moderately vulnerable
Environmental Specificity: Narrow. Specialist or community with key requirements common.
Other NatureServe Conservation Status Information
Inventory Needs: Full geographic inventory badly needed; especially recent data in northern half of range.
Protection Needs: Promote management that restricts alterations to streams; entire hydrographic basin protection is needed to insure long-term survival.
(20,000-200,000 square km (about 8000-80,000 square miles))
Range includes Pacific drainages from the upper reaches of the Willamette River system, Oregon (west of the Cascades crest), south to the upper San Gabriel River, Los Angeles County, California, including the coast ranges and Sierra Nevada foothills in the United States (Stebbins 2003). The species occurred at least formerly in a disjunct location in northern Baja California: two specimens (identified by R. C. Stebbins and R. G. Zwiefel) were collected in 1965 at an elevation of 2,040 meters at the lower end of La Grulla Meadow, Sierra San Pedro Martir, Baja California, Mexico (Loomis 1965); subsequent searches have not detected the species in that area (Grismer 2002, Stebbins 2003). The species apparently has disappeared from portions of its historical range, especially in southern California (see Hayes and Jennings 1988). Extant R. boylii populations are not evenly distributed in California; in the Pacific Northwest, 40 percent of the streams support populations, whereas that number drops to 30 percent in the Cascade Mountains (north of the Sierra Nevada), 30 percent in the south coast range (south of San Francisco), and 12 percent in the Sierra Nevada foothills (Fellers 2005). Elevational range extends from sea level to around 2,130 meters.
U.S. States and Canadian Provinces
Endemism: occurs (regularly, as a native taxon) in multiple nations
U.S. & Canada State/Province Distribution
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.
For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.
Range Map Compilers: IUCN, Conservation International, NatureServe, and collaborators, 2004
U.S. Distribution by County
||County Name (FIPS Code)
Contra Costa (06013),
Del Norte (06015),
El Dorado (06017),
Los Angeles (06037)*,
San Benito (06069),
San Joaquin (06077)*,
San Luis Obispo (06079),
San Mateo (06081),
Santa Barbara (06083)*,
Santa Clara (06085),
Santa Cruz (06087),
* Extirpated/possibly extirpated
U.S. Distribution by Watershed
||Watershed Name (Watershed Code)
Upper Deschutes (17070301)+,
Middle Fork Willamette (17090001)+,
Coast Fork Willamette (17090002)+,
Upper Willamette (17090003)+*,
North Santiam (17090005)+*,
South Santiam (17090006)+,
North Umpqua (17100301)+,
South Umpqua (17100302)+,
Upper Rogue (17100307)+,
Middle Rogue (17100308)+,
Lower Rogue (17100310)+,
Upper Eel (18010103)+,
Middle Fork Eel (18010104)+,
Lower Eel (18010105)+,
South Fork Eel (18010106)+,
Upper Klamath (18010206)+,
Lower Klamath (18010209)+,
South Fork Trinity (18010212)+,
Lower Pit (18020003)+,
Sacramento headwaters (18020005)+,
Upper Stony (18020115)+,
Upper Cache (18020116)+,
North Fork Feather (18020121)+,
East Branch North Fork Feather (18020122)+,
Middle Fork Feather (18020123)+,
Upper Yuba (18020125)+,
Upper Bear (18020126)+,
North Fork American (18020128)+,
South Fork American (18020129)+,
Cow Creek (18020151)+,
Cottonwood Creek (18020152)+,
Battle Creek (18020153)+,
Clear Creek-Sacramento River (18020154)+,
Paynes Creek-Sacramento River (18020155)+,
Thomes Creek-Sacramento River (18020156)+,
Big Chico Creek-Sacramento River (18020157)+,
Upper Putah (18020162)+,
Lower Sacramento (18020163)+,
Upper Kern (18030001)+,
South Fork Kern (18030002)+*,
Upper Deer-Upper White (18030005)+*,
Upper Tule (18030006)+,
Upper Kaweah (18030007)+*,
Upper Dry (18030009)+,
Upper King (18030010)+*,
Tulare-Buena Vista Lakes (18030012)+,
Middle San Joaquin-Lower (18040001)+,
Middle San Joaquin-Lower (18040002)+,
San Joaquin Delta (18040003)+,
Upper San Joaquin (18040006)+,
Upper Chowchilla-Upper Fresno (18040007)+,
Upper Merced (18040008)+,
Upper Tuolumne (18040009)+,
Upper Stanislaus (18040010)+,
Upper Calaveras (18040011)+,
Upper Mokelumne (18040012)+,
Upper Cosumnes (18040013)+,
Panoche-San Luis Reservoir (18040014)+,
Suisun Bay (18050001)+,
San Pablo Bay (18050002)+,
San Francisco Bay (18050004)+,
Tomales-Drake Bays (18050005)+,
San Francisco Coastal South (18050006)+,
San Lorenzo-Soquel (18060001)+,
Central Coastal (18060006)+,
Santa Ynez (18060010)+*,
Santa Barbara Coastal (18060013)+*,
Santa Clara (18070102)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: A small, plain or mottled frog with the undersides of the hind limbs yellow.
General Description: This is a s small frog, gray, brown, reddish, or olive above, and often spotted or mottled with dusky, sometimes plain. Adults have yellow on the underside of the hind legs, extending onto the lower abdomen. A pale triangle is present between tip of the snout and the eyes. The throat and chest often are dark spotted. This species lacks a dark mask. The skin has a granular texture. Dorsolateral folds are indistinct. Young have faint or no yellow pigment on the hind limbs. Adult males have a swollen, darkened thumb base. Adult snout-vent length usually is 3.7-7.1 centimeters. Source: Stebbins (1985).
Diagnostic Characteristics: This frog differs from red-legged frogs (Rana aurora, Rana draytonii) in having yellow (vs. red) on the hind limbs, no dark mask, no well-developed dorsolateral folds, and rough rather than smooth eardrums (Stebbins 1985). It differs from other yellow-legged frogs (Rana muscosa, Rana sierrae) in its rougher skin, lesser spotting and mottling dorsally, presence of a pale triangle on snout (usually absent in the other species), and undarkened toe tips (Stebbins 1985). It differs from tailed frogs in having (in bright light) a horizontal pupil (vs. vertical) and an outer hind toe that is not thicker than the other toes (Stebbins 1985).
Reproduction Comments: Breeding occurs between mid-March and early June, after stream flow subsides from winter storms and runoff. Wheeler et al. (2003) observed newly deposited clutches in early to mid-May in northwestern California. Eggs often are laid in clusters of about 1,000 eggs/mass (Nussbaum et al. 1983). Larvae hatch in about 5 days at 20 C, and metamorphose in summer.
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): CREEK, High gradient, MEDIUM RIVER, Moderate gradient, Pool, Riffle, SPRING/SPRING BROOK
Palustrine Habitat(s): Riparian
Special Habitat Factors: Benthic
Habitat Comments: This species inhabits partially shaded, rocky streams at low to moderate elevations, in areas of chaparral, open woodland, and forest (Nussbaum et al. 1983, Hayes and Jennings 1988). It seeks cover at the bottom of a pool when startled. Habitats in order of decreasing favorability: (1) partially shaded, small perennial streams, at elevations of 30-1,000 meters, with at least some cobble-sized rocks; riffle areas and stream depth rarely greater than 1 meter, (2) intermittent, small, partly shaded, rocky streams displaying seasonal riffle habitat, (3) large (consistently greater than 1 meter in stream depth), partly shaded, perennial streams with rocky or bedrock habitat, (4) open perennial streams with little or no rocky habitat.
Breeding occurs in pools of streams. Eggs usually are attached to gravel or rocks at pool or stream edges(Nussbaum et al. 1983). In northern California, eggs were attached to cobbles and boulders at lower than ambient flow velocities, near confluences of tributary drainages in wide, shallow reaches; most breeding sites were used repeatedly (Kupferberg 1996).
Adult Food Habits: Invertivore
Immature Food Habits: Herbivore
Food Comments: Adults are mainly invertivorous; larvae eat algae, organic debris, plant tissue, and minute organisms in water.
Adult Phenology: Diurnal, Hibernates/aestivates
Immature Phenology: Diurnal, Hibernates/aestivates
Phenology Comments: These frogs are inactive in cold temperatures and redice activity during hot, dry weather. Usually they are most active during daylight hours.
Length: 8 centimeters
Not yet assessed
Stewardship Overview: This species would benefit from streamflow management that avoids aseasonal flow fluctuations (Kupferberg et al. 2009).
Conservation of R. boylii may be enhanced by maintaining or restoring channels with shapes that provide stable breeding sites over a range of river stages (Kupferberg 1996). "Restoration practices and land use changes that affect the relative sediment supply and local geomorphic processes in a stream may directly impact the suitability of habitat complexity required by R. boylii" (Yarnell 2005). New breeding habitat can be created; populations have responded to "bank feathering" restoration projects within one year of construction (Lind et al. 1996).
Monitoring Requirements: Searches for this species at the wrong season can often be unproductive.
Biological Research Needs: Obtain data on hibernation sites, dynamics of local colonization/extinction, habitat utilization of larval stages, basic demography.
Group Name: Ranid Frogs
Use Class: Not applicable
Subtype(s): Breeding Location
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including larvae or eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy major highway, especially at night, such that frogs rarely if ever cross successfully; urban development dominated by buildings and pavement; habitat in which site-specific data indicate the frogs virtually never occur.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: BARRIERS/UNSUITABLE HABITAT: Rivers may or may not be effective barriers, depending on stream width and flow dynamics; identification of streams as barriers is a subjective determination. Ranid frog species vary in habitat use, but even the most aquatic species may traverse upland habitat when conditions are suitable (Pope and Matthews 2001); natural and seminatural upland habitat generally does not constitute a barrier. Here, unsuitable habitat refers to upland habitat devoid or nearly devoid of wetlands, streams, ponds, or lakes. Bodies of water dominated by predatory fishes may be barriers to some species but suitable habitat for others; in most cases, such waters probably should be regarded as unsuitable habitat.
SUITABLE HABITAT: Suitable habitat includes riparian/riverine corridors, wetlands, and wetland/upland mosaics in which wetland patches are separated by less than 1 km of upland habitat; it also includes any upland habitat regularly used for feeding or wintering (e.g., mesic forest for wood frogs).
MOVEMENTS: Available information indicates that individual ranids occasionally move distances of several km (R. luteiventris: Reaser 1996, cited by Koch et al. 1997; R. blairi: Gillis 1975) but most individuals stay within a few kilometers of their breeding sites (R. aurora draytonii: USFWS, Federal Register, 11 September 2000; R. capito: Franz et al. 1988; R. clamitans: Lamoureux and Madison 1999; R. luteiventris: Turner 1960, Hollenbeck 1974, Bull and Hayes 2001). Similarly, maximum distance between capture points generally is a few kilometers or less (R. aurora: Hayes et al. 2001; USFWS, Federal Register, 11 September 2000; R. catesbeiana: Willis et al. 1956; R. luteiventris: Reaser and Pilliod, in press; Engle 2000; R. muscosa: Pope and Matthews 2001). Dispersal data for juveniles are lacking for most species.
Adult and juvenile R. sylvatica readily traveled in excess of 300 m from their pools of origin (Vasconcelos and Calhoun 2004). Bellis (1965) determined that adult and juvenile R. sylvatica in a peat bog had traveled at least 410 m from the nearest breeding pool. Berven and Grudzien (1990) found that dispersing R. sylvatica juveniles traveled an average of 1,208 m from their natal pools. In the Shenandoah Mountains, data for R. sylvatica indicated that ponds separated by a distance greater than 1,000 m should experience little gene flow (Berven and Grudzien 1991). In contrast, populations in Minnesota were very similar in allelic frequencies, even at distances greater than several kilometers (Squire and Newman 2002). However, sample sizes and number of loci examined were small, and genetic patterns do not necessarily reflect movement distances.
The preponderance of data for ranids indicate that a separation distance of several kilometers may be appropriate for suitable habitat and practical for occurrence delineation, despite occasional movements that are longer and that may allow some genetic interchange between distant populations. The movement data for ranids are here regarded as consistent enough to allow the same separation distance to be used for different species; much of the apparent variation in movements doubtless reflects differences in study methods and in the ability to detect long-distance movements.
Author: Hammerson, G.
U.S. Invasive Species Impact Rank (I-Rank)
Not yet assessed
NatureServe Conservation Status Factors Edition Date: 01Sep2013
NatureServe Conservation Status Factors Author: Hammerson, G., M. R. Jennings, and M. P. Hayes
Element Ecology & Life History Edition Date: 20Dec2010
Element Ecology & Life History Author(s): Hammerson, G.
Zoological data developed by NatureServe and its network of
natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).
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