There are no known adverse effects of Rana boylii on humans.
Foothill yellow-legged frogs often fall prey to various species at all stages of life. Rough skinned newts and Centrarchid fishes, such as green sunfish, are common predators of egg masses and larvae. Sacramento squawfish eat egg masses, tadpoles, and adult frogs. Tadpoles are also food sources for predaceous insects such as diving beetles, water bugs, and water scorpions. Herons, some passerine birds, and raccoons will eat tadpoles and adult frogs. Garter snakes (Thamnophis) feed 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. American bullfrogs have contributed greatly to population declines of foothill yellow-legged frogs due to direct predation along with competition for resources.
Known Predators:
Anti-predator Adaptations: cryptic
Foothill yellow-legged frogs 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
The lifespan of foothill yellow-legged frogs 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 foothill yellow-bellied frogs 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. The nonnative American bullfrog (Lithobates catesbeianus), has caused declines of foothill yellow-legged frog populations as well, due to competition for resources and direct predation.
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 foothill yellow-legged frogs, but the effect on this frog is not yet known.
Range lifespan
Status: wild: 3 (high) years.
Foothill yellow-legged frogs are highly aquatic and 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
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 )
Foothill yellow-legged frogs eat mostly insects. Arthropods (Arthropoda), both aquatic and terrestrial, serve as its main food source. Its most common prey items are various types of spiders (Araneae), beetles (Coleoptera), "true" bugs (Hemiptera), and flies (Diptera). However, specimens have been found with other sources of food within their stomachs, such as grasshoppers (Caelifera), hornets (Vespa), carpenter ants (Camponotus), water snails, small moths, water striders (Gerridae), and stoneflies (Plecoptera).
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 )
Like other frogs, foothill yellow-legged frogs are an important facet of their ecosystem. They consume a great number of insects and may help keep the populations of its prey in check. They also serve 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:
Like other amphibians, foothill yellow-legged frogs are 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. They also consume a lot of insects, perhaps helping to control pest populations.
After the 5 to 37 day incubation period, foothill yellow-legged frog 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.
Development - Life Cycle: metamorphosis
Like most other Ranid frogs, this species has small, paired vocal sacs, however their call 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
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
During the breeding season, adult male foothill yellow-legged frogs 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. Foothill yellow-legged frogs are polygynous. 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, foothill yellow-legged frogs breed 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, and from 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
Foothill 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)
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.
How is a tadpole like a short-sleeved white tee shirt? The answer lies in the Alameda Creek outside San Francisco, California, USA. Ari Daniel Shapiro wades into the issue of dams and biodiversity with two biologists sampling the DNA of this threatened frog in order to save it.
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.
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.
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)
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)
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)
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)
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)
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).
Rana boylii adults are around 3.5 to 7 cm long (Stebbins 1985).
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.
The foothill yellow-legged frog (Rana boylii) is a small-sized (3.72–8.2 cm or 1.46–3.23 in) frog[2] from the genus Rana in the family Ranidae. This species was historically found in the Coast Ranges from northern Oregon, through California, and into Baja California, Mexico as well as in the foothills of the Sierra Nevada and southern Cascade Range in California.[3][4] The foothill yellow-legged frog is a Federal Species of Concern and California State Endangered.[3][5] A federal rule to list four out of six extant distinct population segments (DPS) under the Endangered Species Act was proposed in December 2021.[6]
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.[7]
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.[7]
Both the Columbia spotted frog and the Cascades frog, also part of the genus Rana, live in the northern regions of this frog's territory.
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.[8] 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.[9]
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.[7] High stream velocities, however, may dislodge R. boylii egg masses from oviposition substrates.[10] 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.[7] 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 m attached to rocks underwater in streams and rivers with flow velocities ranging from 0.1 to 0.6 m3/second.[10]
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.[7] 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.
Foothill yellow-legged frogs occur in the Coast Ranges from the Santiam River in Marion County, Oregon south to the San Gabriel River in Los Angeles County and along the west slopes of the Sierra/Cascade mountain ranges in most of central and northern California. Other isolated populations have been reported in the Baja California Norte, in southern California, and at Sutter Buttes in Butte County, California. The species is found at elevations ranging from sea level to 6,700 feet (2,000 m) in Baja California Norte. In California, foothill yellow-legged frog have been recorded in the Sierra as high as 6,000 feet (1,800 m) near McKesick Peak,[11] Plumas National Forest and 6,365 feet (1,940 m) at Snow Mountain[12] at the boundary of Lake and Colusa Counties.[13][3] They are found in flowing streams and rivers with either rocky substrate or sunny banks.[9][14]
R. boylii uses a chemical defense to protect itself from fungal infections, such as the Batrachochytrium dendrobatidis.[15] 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.[16] 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. Exposure to carbaryl, a substance found in common pesticides, has been shown to not kill the frogs but does lower the peptides' abilities to defend the species against invaders like the chytrid, B. dendrobatidis.[15] More research is being done to see the full effects pesticides may have on R. boylii.
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.[7] 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.[17]
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.[17] 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 Nevada, especially south of Highway 80, where pesticides often contaminate rivers, and dams block the essential stream flows.[18]
The foothill yellow-legged frog is a natural prey of diving beetles, water bugs, garter snakes, rough-skinned newts, bullfrogs, and western toads.[7]
The foothill yellow-legged frog (Rana boylii) is a small-sized (3.72–8.2 cm or 1.46–3.23 in) frog from the genus Rana in the family Ranidae. This species was historically found in the Coast Ranges from northern Oregon, through California, and into Baja California, Mexico as well as in the foothills of the Sierra Nevada and southern Cascade Range in California. The foothill yellow-legged frog is a Federal Species of Concern and California State Endangered. A federal rule to list four out of six extant distinct population segments (DPS) under the Endangered Species Act was proposed in December 2021.
