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Northern red-legged frog
Northern red-legged frog
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Northern red-legged frog
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Genus: Rana
Species:
R. aurora
Binomial name
Rana aurora
Baird and Girard, 1852

Northern red-legged frogs (Rana aurora) are an amphibian species in the true frog family. They have greenish- to reddish-brown skin, red hind legs, dark spots across their backs, and dark facial masks. As a member of the genus Rana, this species is considered a true frog, with characteristic smooth skin and a narrow waist. These frogs are distributed along the Pacific coast of the United States and Canada, from Northern California to southwest British Columbia.[2][3] There is some range overlap with the federally protected California red-legged frog.[4] Northern red-legged frogs generally breed from January to March, laying eggs in water with submerged vegetation.[5]

Northern red-legged frogs have decreasing population sizes and are listed as "Least Concern" by IUCN.[3] They are a conservation strategy species in Oregon.[6] These frogs are negatively affected by roads due to their characteristic breeding migration from upland-terrestrial to aquatic habitat.[7] Excessive road fatalities have led to novel volunteer programs and wildlife undercrossing projects to protect urban frog populations in Portland, Oregon.[8][9]

Taxonomy

[edit]

Northern red-legged frogs' genus and species name is Rana aurora. They are in the "true frog" family Ranidae and are one of two amphibian species classified as red-legged frogs, the other being the California red-legged frog (Rana draytonii).

Both species of red-legged frogs were initially described as distinct by Baird and Girard in 1852.[10] At some point after their initial classification, the frogs were grouped as one red-legged frog species (Rana aurora), with northern (Rana aurora aurora) and California (Rana aurora draytonii) subspecies.[11] This classification was eventually reversed with evidence from DNA analysis and identification of distinct anatomical differences.[4] The northern red-legged frog does not have vocal sacs, which are paired in California red-legged frogs.[12]

Analysis of the mitochondrial DNA cytochrome b gene confirms that the northern red-legged frog and the California red-legged frog are distinct species from one another.[4] Despite similar names, the northern red-legged frog is more closely related to its sister species, the Cascades frog (Rana cascadeae), than the California red-legged frog.[4] An earlier, contrasting hypothesis suggested the Cascades frog was more closely related to the Oregon spotted frog (Rana pretiosa) based on similarities in breeding vocalizations and oviposition patterns.[13]

Description

[edit]

Northern red-legged frogs have smooth skin that ranges from greenish- to reddish-brown in color. Their name comes from the bright-red coloration found underneath their relatively long, webbed hind legs. There are variable densities and patterns of dark spots and flecks across the frog's body. Their eyes are golden-brown. A thin, horizontal dark marking extends from the front of their eye to their nostrils, and a light stripe follows their jawline.[14] A reddish-brown mask covers their tympanum. Adults have characteristic Rana species features, including prominent dorsolateral folds (ridges along their backs) along the entire dorsal margin, non-warty skin, and a small waist.[5] The northern red-legged frog has long, powerful legs well adapted to jumping.

Northern red-legged frogs demonstrate sexual dimorphism in their size. Larger females can reach 10.7 cm (4.2 in), and males can reach 8.1 cm (3.2 in), but size varies by location. Both sexes are typically a few inches smaller than these maximums in Washington state.[5]

Noted lookalike species are the California red-legged frog, Oregon spotted frog, and the Cascades frog.[5][15] Northern red-legged frogs are smaller than California red-legged frogs, and demonstrate differences in color pattern, limb length, and eye size.[15] Distinguishing features of the northern red-legged frog from the Oregon spotted frog and Cascades frog include groin coloration, dorsolateral fold length, eye orientation, posture, toe webbing, and terrestrial habitat use.[5]

Distribution

[edit]

The northern red-legged frog is found west of the Cascade mountain range in the Pacific Northwest. Their range includes Northern California, western Oregon, western Washington and southwestern British Columbia, including Vancouver Island.[3][16] It also occurs somewhat less-commonly in the southern Cascade Range.[2] Their California range spans every coastal county from southern Mendocino County northward. These frogs can live at elevations up to 1,426 m (4,680 ft), though is not found above an elevation of 1,200 m (3,937 ft) in Northern California coastal mountain ranges, or above 914 m (3,000) in Washington.[2][5][6] It is considered introduced to Alaska.[17]

The southern limit of the northern red-legged frog ends in Northern California's Mendocino County, as is the case for some other Pacific Northwest amphibians. Most California and northern red-legged frog populations demonstrate genetically distinct mitochondrial DNA in their range overlap, indicating a narrow band of hybridization across the region.[4] One study looking at both California and northern red-legged frog presence in southern Mendocino County did not find widespread distribution in forest streams after analyzing environmental DNA.[18]

Habitat

[edit]
Rana aurora adults have smooth brown or reddish-brown skin with small black markings.

Northern red-legged frogs utilize both upland-terrestrial and aquatic habitats. Overwintering habitat data is sparse, though sword fern associations and terrestrial habitation encompass at least part of this period.[5] The still or slow moving waters of ponds, marshes or streams are essential breeding habitat.[19] These frogs' aquatic habitat includes both vernal and permanent bodies of water with submerged vegetation.[6][7]

This species is considered unusually highly oriented to its aquatic habitat, with a clear preference for thickly vegetated shoreline.[20] Northern red-legged frogs require cover because they are subject to predation by various fishes, snakes, birds, mammals, and even other amphibians.

Northern red-legged frogs demonstrate a preference for breeding ponds with sunny patches.[6] Indirect sunlight allows for eggs to absorb heat while embryos develop.[21] Other research and data suggests that closed-canopy ponds may be tolerated and are preferable for tadpole survival in some populations.[22]

Ecology and behavior

[edit]

Diet

[edit]

Mature R. aurora prey upon terrestrial insects, but will also take small snails and crustaceans.[23] Adults also consume worms, tadpoles, small fish, and even small frogs of other species.[citation needed] Tadpole larvae are herbivorous, and eat algae.[5]

Reproduction

[edit]

Males and females begin to move to the breeding sites as early as October, and sometimes as late as January, depending on latitude, cumulative rainfall for the season, and average temperature.[20] The breeding period generally occurs between January and March.[13][5][6] Adult frogs may spend between one and two weeks at their breeding sites.[6] Observations of adult migration are best made on moonlit nights with light rains. Typically, stable minimum temperatures of 5.5 to 6.5 °C (42 to 44 °F) are required to induce breeding.[citation needed] Females deposit eggs in surface water temperatures of at least 6.1 °C (43 °F).[5] Breeding sites can be either permanent or temporary, with inundation usually necessary into June for successful metamorphosis in Oregon, and late May or June in Northern California.[23]

Male frogs arrive at breeding sites before females. The male is thought to defend his territory using nocturnal displays once he reaches the breeding pond.[citation needed] Courtship behaviors commence in January in the California part of the range, and as late as March in northerly regions.[citation needed] Male courtship vocalizations include underwater breeding choruses unique among ranid species, and mating calls during amplexus.[13][21] Eggs are deposited by gravid females in shallow water and attached to submerged vegetation or twigs during amplexus.[13] Males fertilize the eggs as they are deposited.[24] Egg masses are characteristically deposited seven to 15 cm (5.9 in) below the pond surface and away from the water edge.[14][21] Oviposition generally takes place in densely vegetated, shallow portions of wetlands with little current. In unusual cases, egg masses have been observed in water up to 500 cm in depth.[citation needed]

Partially submerged in clear water, there is a clear, jelly egg mass with a bumpy but smooth texture. Inside the mass are small, round black dots. The entire mass is affixed to a small, woody stem.
Northern red-legged frog egg mass, partially submerged in water and attached to woody stems.

Egg masses are globular in shape, typically about 10 cm (3.9 in) in diameter, and may disperse into an irregular form underwater or float to the surface.[21] Jelly surrounding the eggs swells in size after oviposition due to water uptake.[13] Estimates for the number of eggs contained in each egg mass vary between 500 to 1100 and up to 2,000 eggs.[6][24] Eggs are between 2.0 and 3.0 mm in diameter.[21][24] Eggs generally hatch 3 to 5 weeks after fertilization, which is unusually long for other Rana species.[5] Tadpoles will emerge after hatching; they are oval in shape, and gradually get lighter in color with age.[5] There is a spike in mortality among the tadpoles shortly after hatching due to predation and density of the population.[25] The tadpoles that do survive will metamorphose once they reach 5–7.6 cm (2–3 in), and newly metamorphosed frogs will be smaller; between 2 and 2.5 cm (0.8–1 in).[5][21]

Adults leave the breeding pond soon after the breeding activity is concluded and may migrate about one half kilometer to their summer locations, which are likely to be riparian zones. Juveniles are slow to leave the breeding ponds, tend to find cover in riparian areas, and may readily migrate about 0.5 km (0.3 mi) by summertime.[citation needed]

Other behaviors

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In the northern part of their range, adults may hibernate.[citation needed] When this frog senses danger, it will quickly plunge to depths of one meter or more to seek safety in the benthic zone of a pond.[citation needed]

Conservation

[edit]

Northern red-legged frogs are listed as "Least Concern" by ICUN, though their decreasing population size is noted.[3] Frog populations have been extirpated or have reached near-extinction in some regions of California.[4] They are a designated species of concern by the Oregon Conservation Strategy, Oregon's State Wildlife Action Plan.[6]

Increased distance to forest patches and impervious surfaces—such as roads—negatively impact the presence of northern red-legged frogs. Urban frog populations are at risk due to high rates of pavement and forest habitat degradation.[7]

Road fatalities are a conservation concern for northern red-legged frogs. Each frogs' annual breeding migration from upland forest habitat to lowland wetlands can involve crossing busy roads.[6] For the northern red-legged frog population in Portland, Oregon, road fatalities led to the formation of a volunteer program called the Harborton Frog Shuttle in 2013.[8] Frog migration from upland habitat in Forest Park to the Harborton wetlands involves crossing five lanes of traffic on U.S. Highway 30.[26] During the frog's breeding season, volunteers collect frogs stopped by temporary barriers that prevent them from crossing the roads. People then shuttle the frogs to and from the wetlands. Volunteers have escorted hundreds to thousands of frogs to safety each year.[8][27]

The Palensky wildlife undercrossing is another effort to reduce road fatalities across U.S. Highway 30. The culvert is the first amphibian-specific wildlife crossing structure in Oregon as of 2025, though the culvert is large enough to allow passage of other animals, as well.[9]

References

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Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Northern red-legged frog

View on Grokipedia
from Grokipedia
The Northern red-legged frog (Rana aurora aurora) is a medium-sized species in the family Ranidae, distinguished by its slender build, smooth skin, prominent dorsolateral folds, and striking red or pink pigmentation on the undersides of its hind legs, with adults typically measuring 4.4–10 cm in snout-vent length (females larger than males). This species is highly aquatic and arboreal, favoring lowland moist coniferous forests, riparian zones, and wetlands with dense vegetation for cover, where it spends much of its time foraging in leaf litter or climbing low vegetation. Native to the coastal , it ranges from southwestern (including and the ) through and to northwestern (primarily the Coast Ranges from Del Norte to Mendocino County), generally below 1,200 m elevation and west of the . Breeding occurs from late winter to early spring (January–March in southern parts, February–April northward), with males attracting females through underwater vocalizations and amplecting pairs laying 300–5,000 eggs in gelatinous masses attached to submerged vegetation in shallow, slow-moving waters such as , marshes, or stream pools with emergent plants. Eggs hatch in 5–14 days into tadpoles that graze on and organic , metamorphosing after 3–7 months (or overwintering in some cases), with juveniles dispersing into upland habitats by fall to avoid predation. Adults are carnivorous, preying on a variety of like , crustaceans, and snails, as well as smaller vertebrates including , tadpoles, and occasionally conspecifics or small mammals, using sit-and-wait ambush tactics near water edges. Lifespan in the wild averages 8–10 years, with reached at 2–3 years. Populations have experienced localized declines due to habitat loss from , , and ; introduction of non-native predators like bullfrogs, centrarchid fish, and ; ; and emerging diseases such as , though the species remains relatively stable in core areas of Washington and . Globally, it is assessed as Least Concern by the IUCN due to its wide distribution and adaptability, but it holds protected status in parts of its range, including Special Concern in (COSEWIC) and Blue List in , with management emphasizing preservation, riparian buffers, and control of .

Taxonomy and systematics

Classification

The Northern red-legged frog (Rana aurora) is classified in the family Ranidae, commonly known as the true frogs, within the order Anura (frogs and toads), class Amphibia, phylum Chordata, subphylum Vertebrata, kingdom Animalia. The binomial name Rana aurora was originally described by Spencer Fullerton Baird and Charles Frédéric Girard in 1852, based on specimens from the Puget Sound region in present-day Washington state. Historically, the taxonomy of R. aurora underwent significant revision in the early . For much of the , populations of red-legged frogs ranging from to were treated as a single polytypic species, with the southern form designated as the subspecies Rana aurora draytonii (now the , Rana draytonii). In 2004, comprehensive analyses of sequences, allozymes, and morphological traits demonstrated substantial genetic divergence and limited hybridization, leading to the elevation of R. aurora and R. draytonii as full species; their narrow contact zone occurs in southern Mendocino County, . This split clarified the distinct evolutionary trajectories of northern and southern populations, with R. aurora restricted to regions north of this boundary. Currently, Rana aurora is recognized as a monotypic with no . Phylogenetically, it belongs to a western North American of Rana (previously classified under the subgenus Amerana), which forms a to the Eurasian Rana temporaria species group, based on molecular data from mitochondrial and nuclear genes. This positioning highlights its close affinities to other North American ranids such as Rana luteiventris (Columbia spotted frog) and Rana pretiosa (Oregon spotted frog).

Etymology and history

The scientific name Rana aurora derives from the Latin genus Rana, meaning "frog," which has been used since antiquity to denote members of this family, likely mimicking the sound of their calls. The specific epithet aurora, also Latin, translates to "dawn" and alludes to the bright reddish-orange coloration on the undersides of the frog's hind legs, evoking the hues of a sunrise. The northern red-legged frog was first formally described in 1852 by American naturalists Spencer Fullerton Baird and Charles Frédéric Girard, based on specimens collected during the U.S. Exploring Expedition (1838–1842) led by Lieutenant Charles Wilkes. These specimens originated from the Puget Sound region near the Columbia River in what is now Washington state, marking an early contribution to North American herpetology from this landmark naval survey of the Pacific coast. The description appeared in a report on reptiles from the expedition, distinguishing R. aurora from related species based on morphological traits like leg color and body proportions. Throughout the late 19th and early 20th centuries, R. aurora featured in regional surveys of amphibians, including those by the U.S. Biological Survey and early state natural history collections, which documented its presence in coastal wetlands and forests from to . Taxonomic confusion arose soon after description, as R. aurora was frequently lumped with the closely related (Rana draytonii), also described by Baird and Girard in 1852, due to overlapping ranges and subtle morphological differences; by the mid-20th century, they were often treated as (R. a. aurora and R. a. draytonii). This ambiguity persisted until the , when biochemical analyses by Hayes and Miyamoto () provided initial genetic evidence for their distinction as separate . Further resolution came in the 1990s and 2000s through molecular studies, particularly (mtDNA) sequencing, which confirmed deep phylogenetic divergence and a narrow hybrid zone in ; a seminal 2004 analysis by Shaffer et al. solidified the split, emphasizing ecological and genetic isolation. Early research milestones included 19th-century expedition records that established basic distribution, while detailed breeding observations emerged in the 1970s, with studies like Brown (1975) documenting clutch sizes, embryonic development, and seasonal timing in northwestern Washington populations.

Physical characteristics

Morphology

The Northern red-legged frog (Rana aurora) is a medium-sized , with adults measuring 4 to 10 cm in snout-vent length (SVL). The skin is smooth and moist, characteristic of semi-aquatic ranids, with a slightly rugose texture on the undersides. The dorsal coloration ranges from greenish-brown to reddish-brown, often adorned with small, indistinct black spots or flecks forming a network pattern. The ventral surface is pale yellow to creamy white, marked with dark flecks or marbling, while the undersides of the hind legs and exhibit prominent or pinkish pigmentation on a yellowish background. Juveniles may show less intense hues or faint yellowish tints. The head features golden-brown irises with horizontal pupils and laterally oriented eyes, accompanied by a dark mask-like stripe extending from the eye to the , bordered below by a light stripe. Prominent dorsolateral folds run from behind the eyes to the . The limbs are notably long, with the hind legs capable of extending beyond the when folded forward; the hind feet are fully webbed, while the forefeet lack webbing. The body has a distinctive slim waist. Males lack well-developed vocal sacs. Unlike the closely related (R. draytonii), R. aurora exhibits finer spotting and reduced or absent vocal sacs.

Sexual dimorphism

The Northern red-legged frog (Rana aurora) exhibits primarily in body size, with adult females larger than males to support greater egg production. Females reach a maximum snout-vent length (SVL) of up to 10.7 cm, while males reach up to 8.1 cm SVL. This size disparity is evident across populations and contributes to differences in maturation rates, with males reaching at around 2 years and females at 3 years. In terms of coloration and markings, the sexes are largely similar, featuring dorsally tan, , or with dark spots and a distinctive red or orange tint on the undersides of the hind legs and . However, during the breeding season, males may display more pronounced reddish hues on their legs, potentially as a visual cue in mate attraction, though this variation is subtle and not always diagnostic. Overall patterning remains comparable between sexes. Reproductive anatomy shows clear dimorphism adapted to breeding roles. Males lack external vocal sacs but possess paired internal vocal sac rudiments, which support their characteristic underwater calling without surface inflation. During the breeding season (typically late winter to early spring), males develop darkened nuptial pads on their thumbs and enlarged forearms to facilitate , the clasping grip used to ensure of eggs. In contrast, gravid females exhibit noticeably distended abdomens due to developing egg clutches, which can contain hundreds of eggs, further emphasizing their larger body size.

Distribution and habitat

Geographic range

The Northern red-legged frog (Rana aurora) is native to the coastal regions of the in , with its range spanning from Mendocino County in northward through western and Washington to southwestern , including and the adjacent . This distribution is largely confined to areas west of the , encompassing lowlands, forested slopes, and riparian zones along the . Historically, the species was more widely distributed and abundant across this coastal corridor, but populations have experienced local extirpations and declines, particularly in the southern portions of its range in and Oregon's , attributed to alterations and other factors. In contrast, populations remain relatively stable and widespread in , but have experienced declines in Oregon's and parts of , with no significant overall range contraction in core areas. Within its range, the Northern red-legged frog occurs from to about 1,200 m elevation, though it is most frequently encountered below 1,000 m in moist, lowland environments. Introduced populations exist outside the native range, including in (Chichagof Island), Nevada, and Hawaii, but none are documented within this native range, emphasizing its strictly endemic status to these coastal Pacific ecosystems.

Habitat requirements

The Northern red-legged frog (Rana aurora) requires a combination of aquatic and terrestrial habitats to complete its life cycle, with breeding and larval development occurring in shallow, permanent or semi-permanent water bodies such as , marshes, slow-moving , and wetlands featuring emergent vegetation like cattails and sedges. These sites provide submerged stems for egg attachment and quiet waters essential for survival, while avoiding deep or fast-flowing rivers that could disrupt development. Juveniles and adults often utilize ephemeral pools seasonally when available. On land, the species depends on upland forests, including coniferous and types, for and overwintering, where individuals in leaf litter, logs, burrows, and dense riparian zones with canopy cover to maintain . These moist forested areas, often adjacent to breeding sites, support non-breeding phases by offering refuge from . Microhabitat preferences include high humidity and cool temperatures, with activity ranging from 5–25°C; the frog remains inactive during extreme cold or hot, dry conditions but may be active year-round in coastal regions. Water bodies should be pH-neutral, typically around 6–7, as extremes can harm embryos. Seasonally, breeding occurs in lowland aquatic sites from late winter to early spring (typically – depending on ), after which adults and juveniles shift to upland forested areas for the non-breeding period, overwintering under vegetation or in burrows within these habitats. The species is associated with temperate rainforests and coastal ecosystems, where it faces vulnerability to habitat drying driven by , potentially reducing suitable persistence.

Ecology and behavior

Diet and foraging

The Northern red-legged frog (Rana aurora) exhibits a diet that varies by life stage, with adults functioning as carnivorous predators and larvae as herbivores. Adult frogs primarily consume such as beetles, spiders, , grasshoppers, slugs, and other terrestrial and , with prey selection limited by gape size and opportunistic encounters. Larger individuals occasionally ingest small vertebrates, including other amphibians or mice, but dominate the diet year-round. In contrast, tadpoles are herbivorous-detritivorous, grazing on filamentous , scraping it from substrates, and consuming decaying in aquatic environments. Foraging behavior in R. aurora is characterized by ambush predation, where frogs employ a sit-and-wait strategy, relying on visual cues and movement to detect prey before capturing it with a projected sticky . Adults are primarily nocturnal, along shorelines, in riparian vegetation, or on land during wet conditions, while juveniles are active both diurnally and nocturnally and target smaller prey near water margins. This behavior is less efficient in water compared to terrestrial settings, prompting most feeding to occur on land. Seasonal variations in foraging align with activity periods and environmental conditions, with frogs active from late to in their range, hibernating during winter. intake increases during summer months when prey abundance peaks, supplemented by opportunistic scavenging of available items like earthworms during rainy periods. Prey availability is influenced by moist forest and habitats, where dense vegetation supports populations. As a mid-level predator, the Northern red-legged frog occupies secondary and tertiary trophic positions in and riparian food webs, controlling populations including potential pests while contributing to dynamics through predation and nutrient cycling.

Reproduction and life cycle

The Northern red-legged frog (Rana aurora) engages in explosive breeding, with mating concentrated in a brief 1-2 week period that varies regionally. In southern portions of its range, such as , breeding typically occurs from January to March, while in northern areas like Washington and , it shifts to through April. This timing is triggered by increasing rainfall, which stimulates adult movement to breeding sites, and sustained water temperatures above 7°C following periods of milder weather above 6°C. Males produce a weak advertisement call—a stuttering series of 4-5 guttural notes—to attract females, often from submerged positions, leading to axillary amplexus where tactile cues confirm pairing. During amplexus, females release 300–1,300 eggs per (averaging around 600–800 in northern populations) in a single gelatinous mass, attached to submerged or emergent about 7-15 cm below the surface. These egg clusters, up to 10 inches across, are deposited in permanent pools to minimize risk. Eggs hatch into tadpoles in 1-5 weeks, with development time varying inversely with —typically 6-14 days in warmer conditions or up to 35 days at 4.5-7.8°C. Tadpoles, which are dark brown or olive with spotting, feed on and before metamorphosing into juveniles after 3–7 months (some overwintering and transforming after over 12 months), usually by early summer in northern populations. is attained at 2 years for males and 3 years for females, with larger females (as noted in ) capable of producing larger clutches. Wild adults have an average lifespan of 8–10 years, but populations face high juvenile mortality exceeding 90%, primarily from predation during the stage where only about 5% survive to . Eggs and early s are particularly vulnerable to if water levels drop and to predators such as , salamanders, and birds, with no provided to mitigate these risks.

Movement and other behaviors

The Northern red-legged frog (Rana aurora) exhibits seasonal migrations between breeding wetlands and upland habitats, typically covering distances of 300 m to 1–2 km, though some individuals travel up to 4.8 km. These movements occur primarily at night during rainy periods, facilitating travel along riparian corridors and streams to summer areas. Juveniles disperse from breeding sites shortly after , often within days or weeks, while adults undertake longer migrations over extended periods. Locomotion in the Northern red-legged frog relies on powerful hind legs adapted for jumping, allowing leaps of considerable distance relative to body size, often exceeding 1 m to evade threats. In aquatic environments, individuals are proficient swimmers, using reduced toe webbing for efficient propulsion in pools and . They also climb low and traverse undergrowth, employing evasive jumps to navigate terrestrial terrain. Territoriality is minimal outside breeding contexts, with adults showing little toward one another and no established defense of areas. Antipredator responses include initial immobility to avoid detection, followed by rapid fleeing into or dense cover via leaps. During winter, frogs overwinter in aquatic sites or terrestrial refuges such as burrows and under logs, entering to endure cold temperatures without freeze tolerance. Social structure is simple, featuring loose aggregations at breeding sites but lacking complex hierarchies or cooperative behaviors.

Conservation

Threats

The Northern red-legged frog faces multiple anthropogenic and natural threats that contribute to declines across its range, particularly in coastal lowlands and forested wetlands. loss and degradation from , , and are primary concerns, as these activities fragment wetlands, drain breeding ponds, and alter canopies essential for retention and . Road construction exacerbates this by blocking migration routes and causing high rates, with studies documenting up to 92% declines near new highways. Livestock and stream channelization further degrade riparian zones, reducing suitable terrestrial . Pollution from agricultural runoff, including pesticides, nitrates, and , contaminates breeding sites and impairs development, with toxicity affecting embryos and tadpoles in areas like the Fraser Lowlands. The chytrid fungus poses an emerging disease threat, detected in populations since 2008, though mortality impacts remain limited; warmer conditions may heighten susceptibility. Forestry herbicides and urban pollutants add to these risks by accumulating in aquatic environments. Invasive species, notably the (Lithobates catesbeianus) and introduced fish such as bass and , prey on larvae and compete for resources, leading to reduced tadpole survival and habitat exclusion. These invasives thrive in modified permanent ponds created by human activities, amplifying their impact in the . Climate change intensifies vulnerabilities through altered precipitation patterns that cause pond drying and increased drought frequency, disrupting breeding cycles. Rising temperatures and storm events exacerbate habitat degradation, elevate disease risks like chytridiomycosis, and facilitate bullfrog range expansion. Sea-level rise in coastal areas introduces saltwater intrusion, lethal to embryos at concentrations above 4.5%. Other factors include minor collection for the pet trade and stochastic events like severe droughts, which can eliminate local populations but affect a smaller portion of the range compared to ongoing anthropogenic pressures.

Status and management

The Northern red-legged frog (Rana aurora) is classified as Least Concern on the IUCN Red List, a status assigned in 2004, though the global population is experiencing an overall decreasing trend due to localized declines. In the United States, it holds no federal listing under the Endangered Species Act, but state-level designations vary: it is considered Sensitive in Oregon, reflecting ongoing vulnerabilities as of 2025, and Apparently Secure in Washington per NatureServe rankings. In Canada, the species is listed as Special Concern under Schedule 1 of the Species at Risk Act, with provincial status as Blue-listed in British Columbia, indicating a vulnerability ranking of S3S4. Population trends show stability in core habitats of Washington and northern Oregon, where the species remains widespread, but rangewide long-term declines of 30–50% have occurred since the mid-20th century, with notable impacts in and attributed to habitat loss and other pressures. Overall adult population estimates range from 100,000 to 1,000,000 individuals across its range, though precise monitoring remains challenging due to the species' cryptic nature and dispersed sites. Management efforts emphasize habitat protection and restoration, including wetlands enhancement to support breeding and overwintering sites, as outlined in Oregon's Conservation Strategy where the frog has been a focal species since 2016. Innovative mitigation for road mortality includes the Harborton Frog Shuttle, or "frog taxi," in , operational since the early 2020s, which transports frogs across U.S. Highway 30 during migrations through volunteer efforts; Oregon's first amphibian underpass under the highway was completed in late 2024 to further aid passage in 2024–2025 projects. In , management aligns with the federal Species at Risk Act through recovery strategies focusing on habitat connectivity. Recent research from 2024–2025 highlights connectivity improvements, such as under-road crossings in Portland's Forest Park, which enhance migration success and genetic exchange, while broader studies explore climate adaptation measures like preservation to counter warming trends. Ongoing monitoring programs, including those by state wildlife agencies, track population responses to these interventions without evidence of recovery sufficient for status upgrades.

References

  1. https://amphibiaweb.org/species/4987
  2. https://www.env.gov.bc.ca/wld/frpa/iwms/documents/Amphibians/a_redleggedfrog.pdf
  3. https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=1494
  4. https://wdfw.wa.gov/species-habitats/species/rana-aurora
  5. https://animaldiversity.org/accounts/Rana_aurora/
  6. https://www.inaturalist.org/taxa/25545-Rana-aurora
  7. https://collections.si.edu/search/detail/edanmdm:nmnhvz_6005855
  8. https://a100.gov.bc.ca/pub/eswp/speciesSummary.do?id=19586
  9. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/northern-red-legged-frog-2015.html
  10. https://pubmed.ncbi.nlm.nih.gov/15315679/
  11. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.100633/Rana_aurora
  12. https://californiaherps.com/frogs/pages/r.aurora.html
  13. https://www.sciencedirect.com/science/article/abs/pii/S1055790304003240
  14. https://www.researchgate.net/publication/8112136_Phylogeny_of_the_New_World_True_Frogs_Rana
  15. https://pages.uoregon.edu/titus/herp_old/aurorahistory.htm
  16. https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_red_legged_frog_e.pdf
  17. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-294X.2004.02285.x
  18. https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_red_legged_frog_e1.pdf
  19. https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=190359
  20. https://bcreptilesandamphibians.ca/northern-red-legged-frog/
  21. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=68
  22. https://a100.gov.bc.ca/pub/eswp/esr.do?id=19586
  23. https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1934742
  24. https://a100.gov.bc.ca/pub/acat/public/viewReport.do?reportId=52503
  25. https://nwcasc.uw.edu/science/project/assessing-western-sword-fern-microhabitat-for-northern-red-legged-frogs-a-possible-refuge-in-a-changing-climate/
  26. https://oaresource.library.carleton.ca/wcl/2016/20160503/CW69-14-713-2015-eng.pdf
  27. https://www.wildlifeprofessional.org/western/transactions/transactions_1997_12.pdf
  28. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/management-plans/northern-red-legged-frog-2017.html
  29. https://www.registrelep-sararegistry.gc.ca/virtual_sara/files/plans/mp_northern_red_legged_frog_e_proposed.pdf
  30. https://bcreptilesandamphibians.ca/wp-content/uploads/2024/02/licht_1969-1.pdf
  31. https://ecotox.oehha.ca.gov/citation/reproduction-and-development-red-legged-frog-rana-aurora-northwestern-washington
  32. https://esajournals.onlinelibrary.wiley.com/doi/10.2307/1935670
  33. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/red-legged-frog/chapter-7.html
  34. https://wdfw.wa.gov/sites/default/files/publications/01479/wdfw01479.pdf
  35. https://www.registrelep-sararegistry.gc.ca/virtual_sara/files/plans/mp_northern_red_legged_frog_e_final.pdf
  36. https://www.oregonconservationstrategy.org/strategy-species/northern-red-legged-frog/
  37. https://www.opb.org/article/2024/11/23/portland-northern-red-legged-frog-taxi-species-migration/
  38. https://portlandtribune.com/2024/12/26/oregons-first-amphibian-underpass-northern-red-legged-frogs-get-safe-passage-under-highway-30/
  39. https://publications.gc.ca/site/eng/9.831203/publication.html
  40. https://www.pbs.org/video/frog-taxi-9tlwyy/
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