Overview

Comprehensive Description

The endemic river-dwelling Foothill Yellow-legged Frog (Rana boylii) of California and Oregon (U.S.A.) has disappeared from over 50% of historically occupied localities, with absences more common in close proximity to large dams. Persisting populations are small relative to those in rivers without reservoirs and are harmed by poorly timed flow releases and habitat fragmentation. A general population model developed for this species indicates that many R. boylii populations are at risk of extirpation by virtue of low abundance, even before hydrologic stressors and non-native predators (such as bull frogs or bass) are considered. (Kupferberg et al. 2009 (see report here); Sarah Kupferberg, in litt. August 2010)

Recent radiotelemetry and genetic research shows that these frogs use entire watersheds, sometimes migrating many kilometers to mate and lay eggs at breeding sites that are used year after year. To be successful, their unique survival strategy requires use of all habitats from small creeks to big rivers within a basin. Tadpoles cannot mature into frogs without access to sunlit channels with abundant algal foods in the summer, while juveniles and adults cannot survive winter floods without access to refugia such as small tributaries. During the past 150 years, humans have permanently and drastically transformed riverscapes in the Sierran foothills and the Pacific coast-ranges. This human appropriation of rivers is likely to intensify as we search for carbon-neutral methods to produce electricity (e.g., harnessing hydropower), provide drinking water to urban centers, and deliver irrigation to agricultural users. Current listing status as a California Species of Special Concern does not provide adequate protection for these frogs. (Sarah Kupferberg, in litt. August 2010)

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Description

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. 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).

Male Rana boylii establishing its territory.

Run-time: 1:55.
Video submitted by Pierre Fidenci.
Male and gravid female Rana boylii during mating season.

Run-time: 1:24.
Videos submitted by Pierre Fidenci.

  • 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.
  • Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
  • 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.
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Distribution

Global Range: (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.

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occurs (regularly, as a native taxon) in multiple nations

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Range Description

This species is known from the 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 coastal ranges and Sierra Nevada foothills, in the USA. There is a disjunct population at La Grulla Meadow, Sierra San Pedro Martir, Baja California, Mexico. It has apparently disappeared from portions of its historical range, especially in southern California (see Hayes and Jennings 1988). It occurs from sea level up to 2,040m asl.
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Distribution and Habitat

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, 2040m), 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 Juaquin Co., CA, perhaps a stray from the Sierran 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 and sunny banks. When frightened, it dives to the bottom and takes refuge among stones, silt, or vegetation. (Stebbins 1985)

  • 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.
  • Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
  • 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.
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Geographic Range

Rana boylii, foothill yellow-legged frogs, were historically found in the majority of Pacific drainages west of the Cascade Mountain crest from Marion County, Oregon to Los Angeles County, California, and was considered one of the most abundant amphibians in the area. Recently, however, the abundance and distribution status of this species has significantly declined. Today, these frogs are unevenly distributed in the Pacific northwest. While still ranging from western Oregon to southern California (near Los Angeles County), they are present in fewer drainages than before. Populations that were previously found in the San Gabriel Mountains or along the south coast of Monterey County, for example, no longer exist, and there is only a limited number of individuals remaining in the foothills of the southern Sierra Nevada Mountains.

Biogeographic Regions: nearctic (Native )

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Rana boylii ranges from western Oregon to southern California (Los Angeles County near the coast and Kern County inland, absent from the Central Valley) (Behler and King 1979). It is found west of the crest of the Cascade Mountains in Oregon, south in the coastal mountains of California to the San Gabriel River (Los Angeles County); in the Sierra Nevada foothills to about 1830 meters; and in other isolated populations in California. (Stebbins 1985)

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Physical Description

Morphology

Physical Description

Post-metamorphic Rana boylii range from 3.8 to 8.1 centimeters (1.5 to 3.2 inches) in size. Dorsal colors often resemble those of the ground, with variations including blackish, dark brown, reddish brown, gray, olive-like, or greenish with varying amounts and strengths of spots and speckles. Some individuals may possess a light spot within a dark area on the upper eyelid. Ventral coloration is typically whitish to yellowish, with a gradient towards yellow at the posterior end of the body and hind limbs. The throat and anterior surface of the femurs often display the most mottling.

These frogs typically have a broad and pointed head. The tympanum is small and not very evident, usually covered with small tubercles, as is the rest of the dorsal body skin. The tibia is elongated and extends more than half the length of the body, with a shorter hind foot that barely reaches half of the tibia length. The hind feet are entirely webbed and there is a slight expansion of the toe tips. Dorso-lateral folds in this species are obscure and vomerine teeth are sometimes not apparent. However, a sacral-hump is rather conspicuous.

Sexual differences include a bulbular swelling covered in minute papillae at the base of the male's first finger's dorsomedial surface. The females lack this rough, swollen area, and have a longer first finger than the males do. Adult females are larger than males, with snout-vent lengths 20 to 25 mm greater. During the mating season, males may be identified by swollen arms and enlarged nuptual pads on their thumbs for use in gripping females during amplexus.

The larger tadpoles are usually olive to olive-gray colored above, with dark brown spots on the tail and fins. There are six or seven labial tooth rows above the mouth and five or six tooth rows below the mouth. May reach 5 cm (2 in) prior to metamorphosis.

Range length: 5 to 9 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

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The Foothill Yellow-legged Frog (Rana boylii) may be gray, brown, reddish, or olive above. It is sometimes plain-colored, but more often spotted and mottled. Colors are usually well matched to the local rocks and soil. This frog has truly yellow legs, with the yellow extending from the underside of the hind legs onto the lower abdomen (on young frogs, yellow on the hind legs may be faint or absent). The snout has a triangular, usually buff-colored patch from its tip to a line connecting the eyelids. No mask is present. The throat and chest often have dark spots. The skin, including the eardrums, is noticeably granular. There are indistinct dorsolateral folds. The male has a swollen and darkened thumb base. (Stebbins 1985)

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Size

Length: 8 cm

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Rana boylii adults are around 3.5 to 7 cm long (Stebbins 1985).

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Diagnostic Description

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).

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Type Information

Syntype for Rana boylii
Catalog Number: USNM 3370
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: ; 1 adult, 1 larva
Preparation: Ethanol
Locality: No Further Locality Data, El Dorado, California, United States, North America
  • Syntype: Baird, S. F. 1854. Proc. Acad. Nat. Sci. Philadelphia. 7 (2): 62.
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Look Alikes

Lookalikes

The Red-legged Frog (Rana aurora) has red on the underside of its hind legs, usually has a dark mask, has well defined dorsolateral folds, and has smooth eardrums. Relative to R. boylii, the Mountain Yellow-legged Frog (Rana muscosa) has smoother skin, generally heavier spotting and mottling dorsally, usually lacks a snout patch, and often has dark toe tips. The Tailed Frog (Ascaphus truei) has eyes with vertical pupils (horizontal in R. boylii) and 5th (outer) hind toe broadest (not enlarged in R. boylii). (Stebbins 1985)

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Ecology

Habitat

California Montane Chaparral and Woodlands Habitat

This taxon can be found in the California montane chaparral and woodlands, a near coastal ecoregion in Central and Southern California, USA. This ecoregion is disjunctive, with a major element in Southern California and another along the Monterey County coast. The ecoregion encompasses most of the Transverse Range that includes the San Bernardino Mountains; San Gabriel Mountains; portions of the Santa Ynez and San Rafael Mountains; Topatopa Mountains; San Jacinto Mountains; the Tehachapi, Greenhorn, Piute, and Kiavah Mountains that extend roughly northeast-southwest from the southern Sierra Nevada; and the Santa Lucia Range that parallels the coast southward from Monterey Bay to Morro Bay.

The California montane chaparral and woodland ecoregion consists of a complex mosaic of coastal sage scrub, lower chaparral dominated by chamise, upper chaparral dominated by manzanita, desert chaparral, Piñon-juniper woodland, oak woodlands, closed-cone pine forests, yellow pine forests, sugar pine-white fir forests, lodgepole pine forests, and alpine habitats. The prevalence of drought-adapted scrub species in the flora of this ecoregion helps distinguish it from similar communities in the Sierras and other portions of northern California. Many of the shared Sierra Nevadan species typically are adapted to drier habitats in that ecoregion, Jeffrey Pine (Pinus jeffreyi) being a good example.

Oak species are an important component of many chaparral and forest communities throughout the ecoregion. Canyon Live Oak, Interior Live Oak, Tanbark Oak (not a true Quercus species), Engelmann Oak, Golden-cup Oak, and Scrub Oak are some examples. Mixed-conifer forests are found between 1371 to 2896 meters elevation with various combinations and dominance of incense cedar, sugar pine, and white fir, Jeffrey Pine, Ponderosa Pine, and mountain juniper. Subalpine forests consist of groves of Limber Pine (Pinus flexilis), Lodgepole Pine, and Jeffrey Pine. Very old individual trees are commonly observed in these relict subalpine forests. Within this zone are subalpine wet meadows, talus slope herbaceous communities, krumholz woodlands, and a few small aspen groves.

In addition to these general vegetation patterns, this ecoregion is noted for a variety of ecologic islands, communities with specialized conditions that are widely scattered and isolated and typically harbor endemic and relict species. Examples include two localities of Knobcone Pine (Pinus attenuata) on serpentine soils, scattered vernal pools with a number of endemic and relict species, and isolated populations of one of North America’s most diverse cypress floras, including the rare Gowen Cypress (Cupressus goveniana goveniana) restricted to two sites on acidic soils in the northern Santa Lucia Range, Monterey Cypress (Cupressus macrocarpa) found only at two coastal localities near Monterey Bay, and Sargent Cypress (Callitropsis sargentii LR/LC) restricted to serpentine outcrops. Monterey Pine (Pinus radiata) is also restricted to three coastal sites near Monterey Bay.

The ecoregion is also home to a few endemic or near-endemic mammalian vertebrates, such as the White-eared Pocket Mouse (Perognathus alticolus EN), a mammal known only to two disjunct mountain ranges in southern California: San Bernardino Mountains in San Bernardino County (ssp. alticolus), and the Tehachapi Mountains, in Kern, Ventura, and Los Angeles counties. The near-endemic fossorial Agile Kangaroo Rat (Dipodomys agilis) is found in the southern disjunctive unit of the ecoregion, and is known only to the Los Angeles Basin and foothills of San Gabriel and San Bernardino mountains in Ventura, Los Angeles, and Riverside counties north to Santa Barbara County and through the southern Sierra Nevada, including Mount Pinos, Tehachapi and San Gabriel mountains, and northern San Fernando Valley. Non-endemic mammals found in the ecoregion include Botta's Pocket Gopher (Thomomys bottae) and Trowbridge's Shrew (Sorex trowbridgii). Some larger vertebrate predators can be found in the ecoregion, including Puma (Puma concolor), Bobcat (Lynx rufus), Coyote (Canis latrans), and Ringtails (Bassariscus astutus).

The ecoregion boasts five endemic and near-endemic amphibians, largely Plethodontid salamanders. Some specific salamander taxa found here are the endemic Tehachapi Slender Salamander (Batrachoseps stebbinsi VU), known from isolated sites in the Caliente Creek drainage, Piute Mountains, and Kern County, California along with scattered populations in the Tehachapi Mountains to Fort Tejon, Kern County; the near-endemic Blackbelly Slender Salamander (Batrachoseps nigriventris); the Monterey Ensatina (Ensatina eschscholtzii); the Channel Islands Slender Salamander (Batrachoseps pacificus), endemic to a narrow range restricted solely on Anacapa, Santa Cruz, Santa Rosa, and San Miguel islands; and the Arboreal Salamander (Aneides lugubris), found only in California and Baja California. A newt found here is the Coast Range Newt (Taricha torosa). Anuran taxa in the ecoregion include the Foothill Yellow-legged Frog (Rana boylii NT); the Southern Mountain Yellow-legged Frog (Rana muscosa EN), a California endemic occurring in several disjunctive populations; and the Northern Red-legged Frog (Rana aurora).

The California montane chaparral and woodlands ecoregions contains a number of reptiles such as the Coast Horned Lizard (Phrynosoma coronatum), who ranges from Northern California to Baja California. Also found here is the Sagebrush Lizard (Sceloporus graciosus); the Western Fence Lizard (Sceloporus occidentalis); the Southern Alligator Lizard (Elgaria multicarinata); and the Side-blotched Lizard (Uta stansburiana). The Two-striped Garter Snake (Thamnophis hammondii) is a restricted range reptile found near-coastally from Monterey County, California southward to Baja California.

The California Condor once inhabited much of the ecoregion, with the western Transverse Range acting today as a refuge for some of the last wild populations, after considerable conservation efforts, especially in the Los Padres National Forest. The Heermann's Gull (Larus heermanni NT) is found in coastal areas of the ecoregion.

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California Central Valley Grasslands Habitat

This taxon is found in the California Central Valley grasslands, which extend approximately 430 miles in central California, paralleling the Sierra Nevada Range to the east and the coastal ranges to the west (averaging 75 miles in longitudinal extent), and stopping abruptly at the Tehachapi Range in the south. Two rivers flow from opposite ends and join around the middle of the valley to form the extensive Sacramento-San Joaquin Delta that flows into San Francisco Bay.

Perennial grasses that were adapted to cool-season growth once dominated the ecoregion. The deep-rooted Purple Needle Grass (Nassella pulchra) was particularly important, although Nodding Needle Grass (Stipa cernua), Wild Ryes (Elymus spp.), Lassen County Bluegrass (Poa limosa), Aristida spp., Crested Hair-grass (Koeleria pyramidata), Deergrass (Muhlenbergia rigens,), and Coast Range Melicgrass (Melica imperfecta) occurred in varying proportions. Most grass growth occurred in the late spring after winter rains and the onset of warmer and sunnier days. Interspersed among the bunchgrasses were a rich array of annual and perennial grasses and forbs, the latter creating extraordinary flowering displays during certain years. Some extensive mass flowerings of the California Poppy (Eschscholzia californica), Lupines (Lupinus spp.), and Exserted Indian Paintbrush (Castilleja exserta) are found in this grassland ecoregion.

Prehistoric grasslands here supported several herbivores including Pronghorn Antelope (Antilocapra americana), elk (including a valley subspecies, the Tule Elk, (Cervus elaphus nannodes), Mule Deer (Odocoileus hemionus), California ground squirrels, gophers, mice, hare, rabbits, and kangaroo rats. Several rodents are endemics or near-endemics to southern valley habitats including the Fresno Kangaroo Rat (Dipodomys nitratoides exilis), Tipton Kangaroo Rat (Dipodomys nitratoides nitratoides), San Joaquin Pocket Mouse (Perognathus inornatus), and Giant Kangaroo Rat (Dipodomys ingens). Predators originally included grizzly bear, gray wolf, coyote, mountain lion, ringtail, bobcat, and the San Joaquin Valley Kit Fox (Vulpes velox), a near-endemic.

The valley and associated delta once supported enormous populations of wintering waterfowl in extensive freshwater marshes. Riparian woodlands acted as important migratory pathways and breeding areas for many neotropical migratory birds. Three species of bird are largely endemic to the Central Valley, surrounding foothills, and portions of the southern coast ranges, namely, the Yellow-billed Magpie (Pica nuttalli), the Tri-colored Blackbird (Agelaius tricolor EN), and Nuttall’s Woodpecker (Picoides nuttallii).

The valley contains a number of reptile species including several endemic or near-endemic species or subspecies such as the San Joaquin Coachwhip (Masticophis flagellum ruddocki), the Blunt-nosed Leopard Lizard (Gambelia sila EN), Gilbert’s Skink (Plestiodon gilberti) and the Sierra Garter Snake (Thamnophis couchii). Lizards present in the ecoregion include: Coast Horned Lizard (Phrynosoma coronatum NT); Western Fence Lizard (Sceloporus occidentalis); Southern Alligator Lizard (Elgaria multicarinata); and the Northern Alligator Lizard (Elgaria coerulea).

There are only a few amphibian species present in the California Central Valley grasslands ecoregion. Special status anuran taxa found here are: Foothill Yellow-legged Frog (Rana boylii NT); Pacific Chorus Frog (Pseudacris regilla); and Western Spadefoot Toad (Pelobates cultripes). The Tiger Salamander (Ambystoma tigrinum) occurs within this ecoregion.

Although many endemic plant species are recognized, especially those associated with vernal pools, e.g. Prickly Spiralgrass (Tuctoria mucronata). A number of invertebrates are known to be restricted to California Central Valley habitats. These include the Delta Green Ground Beetle (Elaphrus viridis CR) known only from a single vernal pool site, and the Valley Elderberry Longhorn Beetle (Desmocerus californicus dimorphus) found only in riparian woodlands of three California counties.

Vernal pool communities occur throughout the Central Valley in seasonally flooded depressions. Several types are recognized including valley pools in basin areas which are typically alkaline or saline, terrace pools on ancient flood terraces of higher ground, and pools on volcanic soils. Vernal pool vegetation is ancient and unique with many habitat and local endemic species. During wet springs, the rims of the pools are encircled by flowers that change in composition as the water recedes. Several aquatic invertebrates are restricted to these unique habitats including a species of fairy shrimp and tadpole shrimp.

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Central Pacific Coastal Forests Habitat

This taxon is found in the Central Pacific Coastal Forests ecoregion, as one of its North American ecoregions of occurrence. These mixed conifer rainforests stretch from stretch from southern Oregon in the USA to the northern tip of Vancouver Island, Canada. These forests are among the most productive in the world, characterized by large trees, substantial woody debris, luxuriant growths of mosses and lichens, and abundant ferns and herbs on the forest floor. The major forest complex consists of Douglas-fir (Pseudotsuga menziesii) and Western hemlock (Tsuga heterophylla), encompassing seral forests dominated by Douglas-fir and massive old-growth forests of Douglas-fir, Western hemlock, Western red cedar (Thuja plicata), and other species. These forests occur from sea level up to elevations of 700-1000 meters in the Coast Range and Olympic Mountains. Such forests occupy a gamut of environments with variable composition and structure and includes such other species as Grand fir (Abies grandis), Sitka spruce (Picea sitchensis), and Western white pine (Pinus monticola).

Characteristic mammalian fauna include Elk (Cervus elaphus), Black-tailed Deer (Odocoileus hemionus), Coyote (Canis latrans), Black Bear (Ursus americanus), Mink (Mustela vison), and Raccoon (Procyon lotor).

The following anuran species occur in the Central Pacific coastal forests: Coastal tailed frog (Ascaphus truei); Oregon spotted frog (Rana pretiosa VU); Northern red-legged frog (Rana pretiosa); Pacific chorus frog (Pseudacris regilla); Cascade frog (Rana cascadae NT), generally restricted to the Cascade Range from northern Washington to the California border; Foothill yellow-legged frog (Rana boylii) and the Western toad (Anaxyrus boreas NT).  A newt found in the ecoregion is the Rough skinned newt (Taricha granulosa).

Salamanders within the ecoregion are: Del Norte salamander (Plethodon elongatus NT);  Van Dyke's salamander (Plethodon vandykei); Western redback salamander (Plethodon vehiculum); Northwestern salamander (Ambystoma gracile);  Olympic torrent salamander (Rhyacotriton olympicus VU), whose preferred habitat is along richly leafed stream edges; Long-toed salamander (Ambystoma macrodactylum), whose adults are always subterranean except during the breeding season; Dunn's salamander (Plethodon dunni), usually found in seeps and stream splash zones; Clouded salamander (Aneides ferreus NT), an aggressive insectivore; Monterey ensatina (Ensatina eschscholtzii), usually found in thermally insulated micro-habitats such as under logs and rocks; Pacific giant salamander (Dicamptodon tenebrosus), found in damp, dense forests near streams; and Cope's giant salamander (Dicamptodon copei), usually found in rapidly flowing waters on the Olympic Peninsula and Cascade Range.

There are a small number of reptilian taxa that are observed within this forested ecoregion, including: Pacific pond turtle (Emys marmorata); Common garter snake (Thamnophis sirtalis), an adaptable snake most often found near water; Northern alligator lizard (Elgaria coerulea); and the Western fence lizard.

Numerous avian species are found in the ecoregion, both resident and migratory. Example taxa occurring here are the Belted kingfisher (Megaceryle alcyon); Wild turkey (Meleagris gallopavo); and the White-headed woodpecker (Picoides albolarvatus) and the Trumpeter swan (Cygnus buccinator), the largest of the North American waterfowl.

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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).

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Habitat and Ecology

Habitat and Ecology
This species inhabits partially shaded, rocky streams at low to moderate altitudes, in areas of chaparral, open woodland, and forest (Nussbaum, Brodie and Storm 1983; Hayes and Jennings 1988). It seeks cover at the bottom of a pool when startled. Its breeding and non-breeding habitats are the following, in order of decreasing favourability: (1) partially shaded, small perennial streams, 30-1,000m asl, with at least some cobble-sized rocks, riffle areas and a stream depth rarely greater than 1m; (2) intermittent, small, partly shaded, rocky streams displaying seasonal riffle habitat; (3) large (consistently greater than 1m in stream depth), partly shaded, perennial streams with rocky or bedrock habitat; and (4) open perennial streams with little or no rocky habitat. Breeding takes place in pools of streams, and eggs are usually attached to gravel or rocks at the edge of pools or streams (Nussbaum, Brodie and Storm 1983). In northern California, eggs were found attached to cobbles and boulders at lower than ambient flow velocities, near confluences of tributary drainages in wide, shallow reaches, and most breeding sites were used repeatedly (Kupferberg 1996).

Systems
  • Terrestrial
  • Freshwater
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Rana boylii is a highly aquatic species and is almost always found in, or within a short distance from, water. The most frequently used habitats are streams, springs, and freshwater lakes, with a preference for rocky-bottomed creeks; it usually occurs in gently flowing water. Slow-flowing creeks or streams with cobble-sized pebbles are preferred egg laying sites for foothill yellow-legged frogs. Adults often spend the majority of their time sitting on rocks in the stream or nearby on the banks. If startled, however, they will immediately leap into the water and swim swiftly to the bottom. In clear waters, they will take cover under overhanging rocks; in streams with muddy bottoms, they will stir up the silt and hide in the mud. They may occur at any elevation from sea level up to 2,040 m.

Range elevation: sea level to 2,040 m.

Habitat Regions: temperate ; freshwater

Aquatic Biomes: rivers and streams; temporary pools

Other Habitat Features: riparian

  • 1951. Amphibians of Western North America. Berkeley and Los Angeles: University of California Press.
  • 1995. Handbook of Frogs and Toads of the United States and Canada. Ithaca and London: Comstock Publishing Associates.
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Rana boylii is a frog of woodland, chaparral, and forest. It is usually found near water, especially near riffles where there are rocks and sunny banks. When frightened, it dives to the bottom and takes refuge among stones, silt, or vegetation. It occurs from sea level to around 2130 meters. (Stebbins 1985)

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Adults are mainly invertivorous; larvae eat algae, organic debris, plant tissue, and minute organisms in water.

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Food Habits

Rana boylii is primarily an insectivorous species. Arthropods, both aquatic and terrestrial, serve as its main food source. Its most common prey items are various types of spiders (order Araneae), beetles (order Coleoptera) , "true" bugs (order Hemiptera), and flies (order Diptera). However, specimens have been found with other sources of food within their stomachs, such as grasshoppers, hornets, carpenter ants, water snails, small moths, water striders, and stoneflies.

Food is often captured by use of the frog's large, sticky tongue to bring the prey towards its mouth, and is generally located by sight. Tadpoles are herbivorous during early stages of development and consume algae, diatoms, and debris by grazing the surface of vegetation and rocks.

Animal Foods: insects; terrestrial non-insect arthropods; mollusks

Plant Foods: algae

Other Foods: detritus

Primary Diet: carnivore (Insectivore )

  • Wegner, K., J. Crayon. 2009. Diets of Three Species of Anurans from the Cache Creek Watershed, California, USA. Journal of Herpetology, 43(2): 275-283.
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Associations

Ecosystem Roles

Rana boylii, similar to other frogs of its kind, is an important facet to the ecosystem. It consumes a great number of insects and may help keep the populations of its prey in check. It serves as a suitable source of food to many predators, and as a host to various endoparasites. Tadpoles contribute by aiding in the control of algal growth.

Amphibians in general are also excellent indicators of environmental quality. Having permeable skin allows waterborne contaminants to enter the body readily and display the effect on the environment much quicker than could be done by other animals, providing managers with more time for change and repair before it is too late.

Commensal/Parasitic Species:

  • Helminth parasites

  • Chanson, J., T. Boucher. 2004. Disappearing Jewels: The Status of New World Amphibians. Arlington, Virginia: NatureServe.
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Predation

Rana boylii often falls prey to various species at all stages of life. Rough Skinned Newts and Centrarchid fishes, such as green sunfish, are common predators to egg masses and larvae. Tadpoles are also food sources for predaceous insects such as diving beetles, water bugs, and water scorpions. Sacramento squawfish, will eat egg masses, tadpoles, and adult frogs. Herons, some passerine birds, and raccoons will eat tadpoles and adult frogs. American bullfrogs have contributed greatly to population declines of Rana boylii due to direct predation along with competition for resources.

Garter snakes (Thamnophis species) however, are a primary predator to Rana boylii, feeding on both tadpoles and post-metamorphic stages. Species such as common garter snakes, terrestrial garter snakes, and Sierra garter snakes are known to eat mainly juvenile frogs, while Oregon aquatic garter snakes have a preference for tadpoles.

Known Predators:

Anti-predator Adaptations: cryptic

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One Species at a Time Podcast

In rivers regulated by dams, a large water release can be disastrous for frogs. The foothill yellow-legged frog population has been wiped out from more than half of its historic range along California’s coast and central valley- an area that contains 800 damns. Many biologists see this tiny amphibian as a canary in the coalmine – an early indication of an ecosystem gone wrong. By studying the DNA of these frogs scientists are examining how big and healthy the remaining populations are.

Listen to the podcast, meet the featured scientists and find intriguing extras on the Learning + Education section of EOL.

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Kupferberg (1997) studied the invasion of the American Bullfrog (Rana catesbeiana) into a northern California river system (in the Angelo Coast Range Reserve, Mendocino County, California) where it is not native. Native Foothill Yellow-legged Frogs (Rana boylii) were nearly an order of magnitude less abundant in reaches where R. catesbeiana was well established. Competition experiments indicated that R. catesbeiana tadpoles caused a significant reduction in both survivorship and growth of R. boylii. Competition appeared to be mediated by competition for algal resources on which both species feed.There was no evidence of behavioral or chemical interference.

Kupferberg et al. (2009) report on outbreaks of a parasitic copepod, the Anchor Worm (Lernaea cyprinacea), on Foothill Yellow-legged Frogs in a northern California river in 2006 and 2008. Lernaea cyprinacea is originally a Eurasian species, but is now far more widespread. These copepods were most frequently found embedded near a hind limb or the cloaca. Infestation rates were much higher downstream. In both years of the study, recently metamorphosed frogs with copepods were, on average, slightly smaller than those not infested and, at least for frogs parasitized early in development, it appeared that morphological abnormalities may result from infestation. Copepod outbreaks were associated with three unusual conditions: high water temperature (in 2006 and 2008); drought induced low flow (2008); and high densities of tadpoles. Kupferberg et al. suggest that increasing summer water temperatures, decreased daily discharge, or a combination of both promote outbreaks of this non-native parasite on this native host and could present a threat to the long-term conservation of R. boylii under the flow regime scenarios predicted by climate change models.

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 - 300

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).

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Global Abundance

2500 - 100,000 individuals

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).

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Life History and Behavior

Behavior

Communication and Perception

Like most other Ranid frogs, this species has small, paired vocal sacs, however the call of Rana boylii is faint and rarely heard. Most of its calls during mating season occur underwater due to the difficulty of hearing in the air within its noisy stream habitat. This frog's call generally consists of low-pitched and raspy croaks, grunts, or oinks given in a series of 4 to 6 notes per second. Other forms of communication are unknown for this species.

Communication Channels: visual ; acoustic

Perception Channels: visual ; tactile ; acoustic

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Behaviour

Rana boylii is primarily diurnal (Behler and King 1979). The voice of Rana boylii is rarely heard. It is a gutteral, grating sound on one pitch or with rising inflection, a single croak lasting 1/2 to 3/4 seconds. Four or five croaks may be delivered in rapid succession followed by a rattling sound, the entire sequence lasting about 2 1/2 seconds. The inconspicuous vocal sac is evident on each side of the throat, in front of the forelimbs. (Stebbins 1985) Recordings of the calls can be heard here.

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Cyclicity

Comments: These frogs are inactive in cold temperatures and redice activity during hot, dry weather. Usually they are most active during daylight hours.

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Life Cycle

Development

After the 5 to 37 day incubation period, Rana boylii tadpoles hatch out and will remain around the egg mass for about a week, possibly aiding in species identification. Larvae can be up to 18 mm in length for the head and body, and 29 mm in length for the tail. Larval growth rate is dependent on water temperature and food availability, but tadpoles normally undergo metamorphosis within three to four months. Similar to other frogs, typical metamorphic features include absorption of the tail, emergence of front limbs, and reorganization of the digestive tract.

Frog maturity often occurs upon reaching a size of 40 mm snout-vent length (SVL). The reproductive organs become functional in the first summer after metamorphosis, but the first breeding activity often occurs in the second post-metamorphic year. Some individuals, however, have been known to reproduce as early as six months after metamorphosis.

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Life Expectancy

Lifespan/Longevity

The lifespan of Rana boylii is currently unknown. One recaptured female was aged at three years, however, longevity may potentially reach 12 years or more based on studies of closely related species.

The individual lifespan of Rana boylii is often limited by many threats, such as predation and parasites, especially helminth worms. Drought leads to congregation of frogs on land and therefore increased risk of predation, while it also makes eggs more susceptible to desiccation. Floods that occur soon after oviposition may detach egg masses from their substrate, decreasing the chances of survival. Loss of habitat, use of pesticides, and introduced fish species also have negative effects on this species.

Increased exposure to UV-B is believed to have a negative impact on egg hatching success in other Ranids, however this has not yet been determined in this particular species. Chytrid fungus has also been found on Rana boylii, but the effect on this frog is not yet known.

The nonnative bullfrog, Lithobates catesbeianus, has caused declines of Rana boylii populations as well, due to competition for resources and direct predation.

Range lifespan

Status: wild:
3 (high) years.

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Reproduction

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.

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During the breeding season, Rana boylii adult males congregate along gravel and cobble bars of the river and establish calling sites. Male movements occur after river flow decreases following the snow thaw. Thus, the breeding season usually begins in April or March. Females arrive later, asynchronously, after the air and water temperatures have warmed further. Breeding migration by adult frogs appears to be limited to small movements along stream corridors. Individuals exhibit site-fidelity to breeding locations that retain optimal breeding conditions.

Males attract females by calling from their specific sites, which later become oviposition sites for laying females. Mate calling normally occurs underwater, but males will also call above water. The call is described as several short grating notes followed by a rattling sound. These calls, however, are faint and don't carry very far.

Mating System: polygynous

At lower elevations, Rana boylii breeds from late March to early May, after the high-water stages of streams subside. At higher elevations, breeding usually takes place from June to August, after the ice and snow has melted from the high-mountain lakes.

Reproduction is aquatic, with external fertilization. Unlike other Ranidae frogs of the area, mating and egg-laying occurs exclusively in the slow-flowing, shallow water of streams and rivers, but not in ponds or lakes.

Eggs are laid in compact, grape-like clusters that are normally attached to the downstream sides of submerged stones, and occasionally vegetation. The eggs have three gelatinous envelopes present, all of which are firm and distinct, and are often black above, and white or light gray tan below. Anywhere from 100 to over 1,000 eggs may be laid per mass, although the average amount is 900. Egg masses normally have size dimension ranges of 2x2x1.5 to 2x4x2.4 inches. In order to hide them from predators, these masses are often covered with a layer of silt for camouflage.

Depending on the water temperature, the eggs may hatch within 5 to 37 days. This development is probably accelerated in warmer temperatures, and slowed in colder ones. Metamorphosis occurs when tadpoles are 3 to 4 months of age, but they do not reach reproductive maturity until 1 to 2 years of age for males and 2 years for females.

Breeding interval: Foothill yellow-legged frogs breed once yearly.

Breeding season: Foothill yellow-legged frogs breed from late March to early May at lower elevations; June to August at higher elevations.

Range number of offspring: 100 to 1000+.

Average number of offspring: 900.

Range time to hatching: 5 to 37 days.

Range time to independence: 3 to 4 months.

Range age at sexual or reproductive maturity (female): 1 to 2 years.

Average age at sexual or reproductive maturity (male): 2 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

Yellow-legged frogs have little parental investment beyond sperm and egg development and mating. Females ensure attachment of egg masses to the downstream side of a substrate in slow-moving water. They will also cover the masses with a layer of silt to help hide them from predators.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female)

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Rana boylii breeds from mid-March to early June, after high water of streams subsides (Stebbins 1985). Egg clusters are attached to the downstream side of submerged rocks (Behler and King 1979). Females are able to find low-flow spots to protect their eggs even when the ambient flow velocity is very swift (Kupferberg 1996; Sarah Kupferberg, in litt. August 2010).

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Skin secretions fight microbes: frogs
 

Skin secretions of some frogs may help protect them from drug-resistant microbes via novel antimicrobial peptides.

   
  "Skin secretions from many species of anurans (frogs and toads) are a  rich source of peptides with broad-spectrum antimicrobial activities  that may be developed into agents with therapeutic potential,  particularly for topical applications." (Conlon & Sonnevend 2010:3)


"Scientistsreported that frog skin contains natural substances  that could be the basis for a powerful new genre of antibiotics 

"Michael Conlon, Ph.D., who reported on the research, noted that the  emergence of drug-resistant bacteria, which have the ability to shrug  off conventional antibiotics, is a growing problem worldwide. As a  result, patients need new types of antibiotics to replace drugs that no  longer work.

 

"'Frog skin is an excellent potential source of such antibiotic  agents,' said Conlon, a biochemist at the United Arab Emirates  University in Al-Ain, Abu Dhabi Emirate. 'They've been around 300  million years, so they've had plenty of time to learn how to defend  themselves against disease-causing microbes in the environment. Their  own environment includes polluted waterways where strong defenses  against pathogens are a must.'

 "The scientists are currently screening skin secretions from more than  6,000 species of frogs for antibiotic activity. So far, they have  purified and determined the chemical structure of barely 200, leaving a  potential bonanza of antibiotic substances awaiting discovery 

"One substance isolated from the skin secretions of the Foothill  Yellow-legged Frog — a species once common in California and Oregon but  now facing extinction — shows promise for killing methicillin-resistant  Staphylococcus aureus (MRSA) bacteria. MRSA is a 'superbug,' infamous  for causing deadly outbreaks of infection among hospitalized patients.  Now it is occurring in settings outside hospitals, including schools,  nursing homes, and day care centers.

 

"The skin of the mink frog, likewise, contains secretions that show  promise for fighting 'Iraqibacter,' caused by multidrug-resistant  Acinetobacter baumanni.

 "Some of the substances could make their way into clinical trials within the next five years, Conlon predicted." (EurekAlert! 2010)
  Learn more about this functional adaptation.
  • Conlon JM; Sonnevend A. 2010. Antimicrobial peptides in frog skin secretions. Methods Mol Biol. 618(1): 3-14.
  • 2010. Frog skin may provide 'kiss of death' for antibiotic-resistant germs. EurekAlert! [Internet],
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Conservation

Conservation Status

NatureServe Conservation Status

Rounded Global Status Rank: 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.

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Narrow. Specialist or community with key requirements common.

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National NatureServe Conservation Status

United States

Rounded National Status Rank: N3 - Vulnerable

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IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2004

Assessor/s
Georgina Santos-Barrera, Geoffrey Hammerson, Gary Fellers

Reviewer/s
Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)

Contributor/s

Justification
Listed as Near Threatened because the species has declined seriously in some areas (but overall probably at a rate of less than 30% over ten years), and the causes of the decline are not well known, thus making the species close to qualifying for Vulnerable.

History
  • 1996
    Not Evaluated
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Rana boylii is currently listed as a California Species of Special Concern, according to the California Department of Fish and Game, and the IUCN Red List labels it as Near Threatened.

Leading causes of the decline of this species include stream scouring, introduction of nonnative species (such as American bullfrogs) habitat loss, the use of pesticides, logging and mining. Any activity that alters stream flow, water temperatures, or stream bed siltation may harm this species.

Some populations of Rana boylii occur in national forests of California and Oregon, a few national, regional, and state parks, as well as on properties owned by The Nature Conservancy. However, these do not necessarily contribute an adequate amount of support for the declining species.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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Global Short Term Trend: Decline of 10-30%

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.

Global Long Term Trend: Decline of 30-70%

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).

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Population

Population
This species has probably been extirpated from the Tehacahapi Mountains southwards, and there have also been severe declines in the central Sierra foothills of California (Drost and Fellers 1996). It is now rare or absent in Oregon (Leonard et al. 1993), moderately common in north-western California and the northern Sierra foothills, and rare or absent in the central and southern Sierra foothills. This species was first recorded in Mexico three decades ago, but almost nothing is known about its biology there.

Population Trend
Decreasing
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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).

  • 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.
  • Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
  • 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.
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Threats

Degree of Threat: High

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).

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Major Threats
Threats to this species include stream scouring (it may negatively impact frogs in stream bed hibernation sites), introduced aquatic species, non-selective logging practices, and stabilization of historically fluctuating stream flows. However, because causes of declines are uncertain, it is difficult to assess the degree to which this species is threatened. S.J. Kupferberg (pers. comm.) found that bullfrog (Rana catesbeiana) larvae perturbed aquatic community structure and exerted detrimental effects on R. boylii populations in northern California but had only a slight impact on Pseudacris regilla.
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Life History, Abundance, Activity, and Special Behaviors

Official: A California species of special concern; a candidate for Federal Listing (Lind et. al. 1996). Trends: 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, occurs (Lind et. al. 1996).

  • 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.
  • Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
  • 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.
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Davidson (2004) found a strong statistical association between declines in populations of Rana boylii (and several related species) and total upwind pesticide use. Davidson suggests that the common perception that field levels of pesticides are extremely low may be a sampling artifact since at any one location the bulk of pesticide applications occurs during a few short time periods. Thus, animals may experience much higher short-term exposure than insufficiently frequent sampling might indicate.

Davidson et al. (2007) studied the effects of the pathogenic chytrid fungus Batrachochytrium dendrobatidis on Rana boylii. They found that chytrid infection reduced growth of newly metamorphosed frogs by around half, but did not significantly increase mortality. Interestingly, Rana boylii skin peptides strongly inhibited chytrid growth in vitro, which may explain why chytrid exposure did not increase mortality. However, skin peptide defenses were significantly reduced after exposure to a sub-lethal dose of the pesticide carbaryl, suggesting that pesticides may inhibit this innate immune defense and increase susceptibility to disease, including chytrid infection. The authors found no statistical interaction between chytrid and pesticide exposure on mortality or growth (i.e., under the conditions of these experiments, there was no evidence of a synergistic effect of pesticide and chytrid exposure on mortality). However, they suggest that this could be because for this well-defended anuran species, even the reduced level of skin peptides present after a single exposure to carbaryl was still sufficient to ward off the lethal effects of chytrid infection. In the field, animals may receive multiple exposures to carbaryl or other pesticides, which might make intensify their effect in increasing susceptibility to chytrid infection. It is also possible that while carbaryl suppressed skin peptide levels, other aspects of the immune system may have protected R. boylii against chytrid infection.

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Management

Biological Research Needs: Obtain data on hibernation sites, dynamics of local colonization/extinction, habitat utilization of larval stages, basic demography.

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Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: Some occurrences are within national forests in California and Oregon, but this does not necessarily provide adequate protection. A few occurrences are in national, regional and state parks, and on TNC properties. In Mexico it occurs within the San Pedro Martir National Park which is a relatively well preserved area. This species is protected by Mexican Law under the "Special Protection" category (Pr).

Needs: Promote management that restricts alterations to streams; entire hydrographic basin protection is needed to insure long-term survival.

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Conservation Actions

Conservation Actions
Some populations of this species occur in national forests in California and Oregon, but this does not necessarily provide adequate protection. It also occurs in a few national, regional and state parks, and on properties owned by The Nature Conservancy. In Mexico it occurs within the San Pedro Martir National Park, which is a relatively well-preserved area. This species is protected by Mexican law under the "Special Protection" category (Pr).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

There are no known adverse effects of Rana boylii on humans.

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Economic Importance for Humans: Positive

Rana boylii, as with other amphibians, is an exceptional indicator of environmental health. Due to its permeable skin, waterborne contaminants can be detected early in this frog by ecosystem managers, allowing time for the necessary action to take place.

Rana boylii also consumes numbers of insects, perhaps helping to control pest populations.

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Risks

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).

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Wikipedia

Foothill Yellow-legged Frog

The foothill yellow-legged frog (Rana boylii) is a small-sized 3.72–8.2 cm (1.46–3.2 in) frog[2] from the Rana genus in the Ranidae family. This species can be found from northern Oregon, down California’s west coast, and into Baja California, Mexico. Both the Columbia spotted frog and the Cascades frog, also part of the Rana genus, live in the northern regions of this frog's territory. They prefer to live in streams and rivers, and lay their eggs in masses attached to rocks underwater.

Appearance[edit]

The frog is part of the olive variety with the yellowish legs.
This frog displays the reddish dorsum.

The foothill yellow-legged frog has a grey, brown, or reddish dorsum, or the back of the frog. It is commonly spotted or mottled, but occasionally is plainly colored. Adults have yellow coloration under their legs, which may extend to their abdomens, but this characteristic is faint or absent in young frogs.

A triangular, buff-colored patch occurs on the snout, and, unlike other frogs in the genus, there is no eye stripe. The throat and chest are often boldly mottled; and the species has indistinct dorsolateral skin folds and granular skin. Males of this species develop nuptial pads on their thumb bases during the breeding season. These frogs can be identified by their rough skin, horizontal pupils, fully webbed hind feet, and their habit of jumping into moving water.[3]

Tadpoles of this species, though, resemble those of the western toad, Bufo boreas. R. boylii as tadpoles have fairly flattened tails that lack color at the end and are the tallest in the midsection. The mouths of the tadpoles are made for suction to rocks, with labial teeth rows used for scraping algae and diatoms, unicellular algae with cells walls that contain silica, off of the rocks to which they are clinging. The mouth of the young R. boylii is also helpful in identifying it from B. boreas because the young foothill yellow-legged frogs develop more defined teeth rows after three weeks, while their counterparts do not.[3]

Food sources[edit]

Food supplies, such as algae the tadpoles eat, also affect the sexual maturity of the species. Reportedly, the “amount of protein in different algae, can affect size at and time to metamorphosis” and “these food effects may be mediated through diet-induced changes in thyroid function”, which means the food the tadpoles ingest dictates the changes in the thyroid gland's production of certain proteins.[4] Tadpoles most commonly feed on algae, diatoms, and detritus. As the species grows older, it changes its diet to animal tissue which must be swallowed whole because the frog's jaw is structured on a hinge joint that does not allow for sideways movement as in humans. Adult frogs eat a range of foods such as moths, ants, grasshoppers, hornets, beetles, flies, water striders, and snails.[5]

Mating habits[edit]

This egg mass is placed between two large rocks.

The mating “ceremonies” begin in spring, when adult frogs congregate on sandy and/or rocky bars to mate. Previously believed to mate from March to May, recent experiments have shown the time to be closer to April to late June.[3] High stream velocities, however, may dislodge R. boylii egg masses from oviposition substrates.[6] Thus, R. boylii avoids rapid waters to protect the egg masses from being swept away. This technique is why the species has a long breeding season. If the conditions do not meet their standards, they refuse to mate and wait until the water velocities go back down to ideal.

For the foothill yellow-legged frog, oviposition, or the depositing of eggs, is somewhat sporadic because delays such as rains could cause problems such as unwanted removal of eggs.[3] The males also perform mating calls mostly underwater, and those above the water are faint and hard to hear over 50 m. After the frogs have successfully mated, the egg masses are laid about 0.5 mr down in the river and with flow velocities ranging from 0.1 to 0.6 m3/second.[6]

These egg masses can contain 100 to 1000 eggs in one batch, contained in a bluish gel that disappears once the eggs take on water, and the dark ovum, the center of egg, is covered by three jelly envelopes about 5.4 mm in diameter. Eggs hatch in about five to over thirty days depending on the temperature that the mass is at and the surrounding water.[3] The tadpoles continue to stay associated with the egg mass for several days, and continue to need higher temperatures to grow quickly. By the time the tadpoles reach about 40 mm, roughly 1.5 in, they are adults and their reproductive organs are mostly functional. The frogs are usually fully developed by the summer after their first metamorphosis, though some begin breeding after six months.

Habitat[edit]

The foothill yellow-legged frog's territory spans from northern Oregon, to California's coast where it most commonly found, and into Baja California, Mexico. They are found in flowing streams and rivers with either rocky substrate or sunny banks.[5]

Chemical defense[edit]

R. boylii uses a chemical defense to protect itself from fungal infections, such as the Batrachochytrium dendrobatidis.[7] The frog secretes a peptide through the skin and the hydrophobic (water repellent) sections of the peptide access to fungi that want to attach to the amphibian.[8] This ability can also be found in other Rana species, including the Cascades frog and the moor frog. The former secretes a milky substance that fights against fungal infections and the latter uses its capability to have males turn blue during mating season. Still, the foothill yellow-legged frog's chemical defense has not been fully examined. Although not much is known about it, this ability of the species has been of interest to many companies because of its overall antifungal effectiveness. However, current pesticide use has caused problems for the frog. So far, exposure to carbaryl, a substance found in common pesticides, has been shown to not kill the frogs, it does lower the peptides’ abilities to defend the species against invaders like the chytrid, B. dendrobatidis.[7] More research is being done to see the full effects pesticides may have on R. boylii.

Environmental issues[edit]

Along with the problems associated with pesticides being washed into this frog's habitat, in Trinity County, California, a dam on the major river of the frog's home has affected about 94% of the possible procreation areas for the frogs, which has endangered the population.[3] One study suggests the “data from a comparably sized undammed river fork in the same system…demonstrated that both the number of potential sites and the total number of egg masses were…higher on this fork than in our main stem”, so the unseasonal flooding required by the dam was negatively affecting the mating behavior of the frog.[9]

The temperature of the water in Trinity County is also lower than it was before the dam was put into place. To keep up with demands of fisheries, the water’s temperature is kept artificially lower than normal, which consequently slows the development of R. boylii.[9] Therefore, the colder temperatures are making it more difficult for the frogs to grow quickly, which sometimes leaves the species prey to many other animals that feed on their young. The problems occurring between the foothill yellow-legged frog and the dam are being handled by several herpetological organizations, along with the Forest Service, to find ways to alter the effects in a beneficial way for the frog. This species is also estimated to be gone from most of its range in the Sierra Nevadas, especially south of Highway 80, where pesticides often contaminate rivers, and dams block the essential stream flows.[10]

Predators[edit]

The foothill yellow-legged frog is a natural prey of diving beetles, water bugs, garter snakes, rough-skinned newts, bullfrogs, and western toads.[3]

References[edit]

  1. ^ Georgina Santos-Barrera, Geoffrey Hammerson and Gary Fellers, 2004
  2. ^ Robert N. Fisher and Ted J. Case, 2003
  3. ^ a b c d e f g Ashton, Don T., Amy J. Lind, and Kary E. Schlick. "Foothill Yellow-Legged Frog (Rana boylii) Natural History." USDA Forest Service (1998).
  4. ^ Kupferberg, Sarah J. "The Role of Larval Diet in Anuran Metamorphosis." American Zoologist 37 (1997): 146-59.
  5. ^ a b "Rana boylii." AmphibiaWeb. 21 Apr. 2009<http://amphibiaweb.org/cgi-bin/amphib_query?where-genus=Rana&where-species=boylii>.
  6. ^ a b Welsh, Jr., Hartwell H., and Clara A. Wheeler. "Mating Strategy and Breeding Patterns of the Foothill Yellow-Legged Frog (Rana Boylii)." Herpetological Conservation and Biology 3(2008): 128-42.
  7. ^ a b Benard, Michael F., and Et al. "Effects of Chytrid and Carbaryl Exposure on Survival, Growth and Skin Peptide Defenses in Foothill Yellow-legged Frogs." Environmental Science and Technology 41 (2007): 1771-776.
  8. ^ Conlon JM, Sonnevend A, Patel M, et al (November 2003). "Isolation of peptides of the brevinin-1 family with potent candidacidal activity from the skin secretions of the frog Rana boylii". The Journal of Peptide Research: Official Journal of the American Peptide Society 62 (5): 207–13. PMID 14531844. Retrieved 2009-04-26. 
  9. ^ a b Lind, Amy J., Hartwell H. Welsh, Jr., and Randolph A. Wilson. "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 (1996): 62-67.
  10. ^ "R boylii." californiaherps 07 Sept 2011<http://www.californiaherps.com/frogs/pages/r.boylii.html#status
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Names and Taxonomy

Taxonomy

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).

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