Animal Diversity Web

Geographic Range

Rana draytonii, also known as the California Red-legged frog, occurs in the state of California within the central and southern areas. Specifically, they are located on the coast from the Point Reyes National Seashore in Marin County, and inland from the City of Redding in Shasta County, southward to northwestern Baja California, Mexico. The following southern coastal Hydrographic Units in Mendocino County: Point Arena, Garcia, and Gualala also contain Rana draytonii frogs. Rana draytonii has reduced 70% of its geographic range with a major decline in population size as a result of multiple environmental and anthropogenic factors, and is now only found within 265 streams or drainages in 28 counties of California. Historically, there were over 60 drainages that supported Rana draytonii frogs at one point. Most of these population declines occurred in the Sierra Nevada and Southern California. In southern California, they have disappeared from the Los Angeles area south to the Mexican border, with the only known population to be located in San Francisquito Canyon on the Angeles National Forest. Occupancy area and subpopulations of Rana draytonii is still occurring to this day, yet the exact rates are unknown. (Brown, 2020; Davidson, 1996; U.S. Fish and Wildlife Service, 2002)

There is an integrated zone between Rana draytonii frog and another closely related species, Rana aurora, that is located from the north of Walker Creek watershed in Marin County to southern Mendocino County. This intergrade zone between Rana draytonii and R. aurora frogs has recently been found narrower as well as Rana draytonii extending 60 miles further north. Rana draytonii and R. aurora were once thought to be considered subspecies of red-legged frogs, but genetic testing has determined that these are considered to be two separate species that have an overlap of their geographical range. (Brown, 2020; Davidson, 1996; US Service, 2020)

• Biogeographic Regions
• nearctic
  • native

Habitat

Rana draytonii typically occupy sheltered backwaters of ponds, marshes, springs, streams, and reservoirs with riparian vegetation. The vegetation allows for hiding from predators, shading to maintain cool water temperatures, and shelter during winter; Rana draytonii cannot survive in water temperatures higher than 29 degrees Celsius. This sheltering habitat can be a factor limiting population numbers and distribution levels of Rana draytonii. Deep waters with dense amounts of willow trees intermixed with cattails are the best habitat for Rana draytonii. In habitats without riparian vegetation, Rana draytonii is found in short-lasting ponds or drainages. Rana draytonii is located within intermittent waters more than permanent waters, due to predators that dominate permanent waters. Winter rains, as well as non-breeding seasons, may cause Rana draytonii frogs to migrate, typically at night. Winter rains have caused adult Rana draytonii frogs to move more than 2 miles in northern Santa Cruz County without regard to the habitat’s vegetation, while non-breeding seasons cause Rana draytonii to migrate towards nearby upland forests. (Brown, 2020; Cole, 1997; US Service, 2020)

• Habitat Regions
• temperate
• terrestrial
• freshwater

• Terrestrial Biomes
• forest

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• temporary pools
• coastal

• Wetlands
• marsh

• Other Habitat Features
• riparian

Physical Description

When Rana draytonii individuals are larvae, they appear as a brown color with tiny dark-colored spots. Their lower body tends to have a lighter white appearance, also covered with speckles. As adults, they have a physical coloring of brown, gray, olive, red, or orange, often with a pattern of dark spots or specks with thick, rough skin. There are typically light centered spots on its dorsal side as well. Rana draytonii frogs typically have a dorsolateral fold running from its eye to its hip. They also possess large, well-developed webbed feet on their hind legs. Along the upper lip from beneath the eye to the bottom of the jaw, they typically have a cream, white, or orange stripe. Rana draytonii has a white underside with bright red or orange patches on the hind legs and abdomen. They have a groin area with bold black mottling with a background of white or yellow. Rana draytonii has been found to be the largest native frog in the western United States with a snout to vent length ranging from 4.5 to 13.3 centimeters. Rana draytonii have sexual dimorphism where females are typically longer and the males during the mating period will enlarge their forearms and gain a pigmented swelling on the thumbs to aid intercourse. (US Service, 2020; Wake, et al., 2020)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger
• ornamentation

• Range length

  4.5 to 13.3 cm

  1.77 to 5.24 in

Development

Breeding sites of Rana draytonii include pools and backwaters with streams and creeks, ponds, lagoons, and even artificial impoundments like stock ponds. Ponds and streams that dry up in the fall are optimum habitats for Rana draytonii breeding because introduced American bullfrogs (Lithobates catesbeianus) that have tadpoles that require over a year to metamorphose will not survive this periodic drying. Rana draytonii frog eggs are typically attached at or near the surface of the water. Six to fourteen days after fertilization, the embryos hatch and the larvae will take three to seven months to obtain metamorphosis. Larvae have a high mortality rate at every life stage considering that less than one percent of eggs that are laid reach metamorphosis. When they do reach metamorphosis, the brown tadpole typically obtains the size of 7.62 centimeters long. They grow legs, lose their tail, and become the juvenile form of the adult frog. (Brown, 2020; Hickman, 1995; U.S. Fish and Wildlife Service, 2002; Wake, et al., 2020)

• Development - Life Cycle
• metamorphosis

Reproduction

Like other temperate Rana species, males and females congregate at breeding sites to mate. (Brown, 2020; Hickman, 1995; US Service, 2020; Wake, et al., 2020)

• Mating System
• polygynandrous (promiscuous)

Reproduction in Rana draytonii frogs occurs from November through March, with earlier breeding in southern frogs. The female Rana draytonii will lay egg masses containing 2000 to 5000 eggs in permanent bodies of water with extensive vegetation during or right after large rainfall events in late winter and early spring, meaning that they are prolific breeders. Once the female individual reaches three years and the male individual reaches two years, they obtain sexual maturity. The juveniles have been found to live diurnally and nocturnally, while adults are found to usually be nocturnal. (Brown, 2020; Hickman, 1995; US Service, 2020; Wake, et al., 2020)

• Key Reproductive Features
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • external
• oviparous

• Breeding interval

  Rana draytonii breed once during winter to early spring

• Breeding season

  Rana draytonii breed November through March

• Range number of offspring

  2000 to 5000

• Range time to hatching

  6 to 14 days

• Range age at sexual or reproductive maturity (female)

  3 (high) years

• Range age at sexual or reproductive maturity (male)

  2 (high) years

Like other temperate Rana species, females deposit eggs into the water and they are fertilized by males. There is no further parental investment (Brown, 2020; Hickman, 1995; US Service, 2020; Wake, et al., 2020)

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning

Lifespan/Longevity

Rana draytonii frogs have been found to live anywhere from 8 to 10 years depending on environmental factors they encounter. Rana draytonii may live for much less time than this average lifespan if they encounter an unfavorable environment. There have not been any long-term experiments observing the dynamics of Rana draytonii populations, therefore it can be hard to determine exactly how long these frogs live for. (U.S. Fish and Wildlife Service, 2002)

• Typical lifespan
  Status: wild

  8 to 10 years

Behavior

Rana draytonii live in thick or developing coastal vegetation as well as motionless transient and persistent bodies of water which are their ideal breeding locations. Rana draytonii is a solitary, primarily diurnal species that breeds over a few days. During periods of flooding, Rana draytonii conceals itself in mammal burrows or small pockets along the banks of rivers. (Brown, 2020; Hayes, 1986; U.S. Fish and Wildlife Service, 2002; US Service, 2020)

• Key Behaviors
• natatorial
• diurnal
• nocturnal
• motile
• solitary

Communication and Perception

For communication between males and females within Rana draytonii species, male frog mating calls are a few minor sequential grunts, usually portrayed while located beneath the water. These amphibians have a sensory perception of environmental cues that can help them locate their desired ponds every year, as well as locating their mates. Male Rana draytonii have been reported to call other males from within a few centimeters apart, without showing signs of aggression. (Brown, 2020; Wake, et al., 2020)

• Communication Channels
• acoustic

• Perception Channels
• acoustic

Food Habits

R. draytonii has a highly variable diet, including invertebrates (such as insects) as the most common item. Some vertebrates eaten by R. draytonii may be the Pacific Chorus Frog, and even larger frogs may eat the California mouse. This species is also known for eating the larvae of salamanders. Larvae R. draytonii will typically eat algae, but they might even eat detritus that is located on various greenery or stones. The age of R. draytonii frogs greatly influences the timing that they feed, considering that young frogs will eat at any time but adults are typically only nightly feeders. (Brown, 2020; U.S. Fish and Wildlife Service, 2002)

• Primary Diet
• carnivore
  • eats terrestrial vertebrates
  • eats eggs
  • insectivore

• Animal Foods
• mammals
• amphibians
• eggs
• insects

• Plant Foods
• algae

• Other Foods
• detritus

Predation

The primary predators of Rana draytonii have been found to be raccoons (Procyon lotor), garter snakes (Thamnophis spp.), and Great Blue Herons (Ardea herodias). It has been argued that predation by introduced fish species has been an element in the reduction of individuals of Rana draytonii. American bullfrogs (Lithobates catesbeianus) has been recognized as a species also responsible for the declines of Rana draytonii, but this relationship is largely unknown. Less frequently, Rana draytonii has been eaten by Black-Crowned Night Herons (Nycticorax nycticorax), American Bitterns (Botaurus lentiginosus), and occasionally by Red-Shouldered Hawks (Buteo lineatus). (Wake, et al., 2020)

• Known Predators

  • raccoons (Procyon lotor)
  • garter snakes (Thamnophis spp.)
  • Great Blue Herons (Ardea Herodias)
  • American bullfrogs (Lithobates catesbeianus)
  • Black-Crowned Night Herons (Nycticorax nycticorax)
  • American Bitterns (Botaurus lentiginosus)
  • Red-Shouldered Hawks (Buteo lineatus)

Ecosystem Roles

Rana draytonii are widely involved with many ecosystem roles, whether being the predator or prey. Rana draytonii larvae have been found to eat algae, allowing for control of algae overpopulation as well as keeping the water content clean. Rana draytonii has established correlations with Pacific tree frogs (Pseudacris regilla), American bullfrogs (Lithobates catesbeianus), and rough-skinned newts (Taricha granulosa). Lithobates catesbeianus are typical predators for Rana draytonii which shows its significance within the food web. Rana draytonii also co-occur with California giant salamanders (Dicamptodon ensatus), California tree frogs (Pseudacris cadaverina), and arroyo toads (Anaxyrus californicus. Rana draytonii frogs have been less frequently associated with Pacific pond turtles (Emys marmorata), western toads (Anaxyrus boreas), Sierra garter snakes (Thamnophis couchi), California newts (Taricha torosa), and common garter snakes (Thamnophis sirtalis). Not only are Rana draytonii a food source for larger animals but they also play a huge role in being able to control the smaller insects and the larger animals, like other frogs and mice, by feeding on them. (Wake, et al., 2020)

Economic Importance for Humans: Positive

Rana draytonii frogs have been used by fisheries since 1849, around the time of the Gold Rush. These fisheries allow for many humans to consume frog legs for food; over 80,000 individuals were harvested for their legs at one point within only a span of one year. Just like other amphibian species, these animals can be used to detect water quality levels as well as the amount of vegetation within an area. Rana draytonii allows for an ecological balance in our ecosystem due to their ability to eat many insects, small mammals, and other invertebrates, as well as being the prey of many other native animals. Therefore, Rana draytonii has the ability to control pests in anthropogenic gardens and within agriculture. Rana draytonii is also extremely beneficial for human health within the medical field because their skin secretions contain multiple antimicrobial peptides that can allow for creating possible pharmaceuticals. The antimicrobial peptides can be in use for creating strains of medicine that prevent pathogenic resistance to occur. (Brown, 2020; Jennings, 1985)

• Positive Impacts
• food
• source of medicine or drug
• research and education
• controls pest population

Economic Importance for Humans: Negative

There are no known adverse effects of R. draytonii on humans.

Conservation Status

Rana draytonii is considered to have a national status of being threatened since 1996, declared by the Fish and Wildlife Services after a Congressional prohibition. Rana draytonii frogs are protected by the federal and California law. Declining populations of Rana draytonii have been found to be due to factors like the degeneration and decrease of habitats through farming, urbanisation, quarrying, logging operations, non-indigenous plants, decreasing water conditions, use of defoliants, and alien predators. Each geographical location has multiple factors performing together allowing for the declining population sizes of Rana draytonii. Rana draytonii have a recovery plan developed to provide rehabilitation for the declining populations of these frogs. The objectives of this recovery plan are to protect existing populations by reducing hazards in order to restore and build new ecological habitats that can be controlled. This plan allows for monitoring population levels of Rana draytonii and to be able to conduct research on the biological threats. Therefore, this plan is used to be able to restore population levels of the species where Rana draytonii had its historical spectrum previously. Some efforts have already been started, such as removing exotic plants, introducing Rana draytonii tadpoles, maintaining dense stands of riparian vegetation, and silt removal. These have been proposed during fall months to not disrupt the breeding season of November through April. (Brown, 2020; US Service, 2020)

• IUCN Red List

  Vulnerable

• US Federal List

  Threatened

Other Comments

The subspecies R. aurora and R. draytonii were previously placed together as a single species because of the recognition of them being considered hybrids from the coastal region of northern California. More recently, new data has determined R. aurora and R. draytonii as separate species by genetic testing. (Camp, 1917)

Contributors

Bethany Long (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Brown, S. 2020. "Animal Diversity Web" (On-line). Accessed March 10, 2020 at https://animaldiversity.org/accounts/Rana_aurora/.

Camp, C. 1917. Notes on the Systematic Status of the Toads and Frogs of California. Berkeley, CA: University of California Publications in Zoology.

Cole, E. 1997. The response of Amphibians to Clearcutting, Burning and Glyphosate Application in the Oregon Coast Range. Journal of Wildlife Management, 61.3: 656-664.

Davidson, C. 1996. "Rana aurora - Red-legged Frog" (On-line). Accessed February 11, 2020 at http://ice.ucdavis.edu/Toads/texthtml/aurora.html.

Hayes, M. 1986. Vocal Sac Variation Among Frogs of the Genus Rana from Western North America. Copeia, 4: 927-936.

Hickman, C. 1995. Animal Diversity. Miami, FL: McGraw-Hill Higher Education.

Jennings, M. 1985. Pre-1900 Overharvest of California Red-Legged Frogs (Rana aurora draytonii): The Inducement for Bullfrog (Rana Catesbeiana). Herpetologica, 41.1: 94-103.

Nafis, G. 2020. "California Herps" (On-line). Accessed April 21, 2020 at http://www.californiaherps.com/frogs/pages/r.draytonii.html.

U.S. Fish and Wildlife Service, 2002. "Recovery Plan for the California Red-legged Frog (Rana aurora draytonii)" (On-line). Accessed March 10, 2020 at https://ecos.fws.gov/docs/recovery_plan/020528.pdf.

US Service, 2020. "California Red-Legged Frog Species Profile" (On-line). Accessed February 11, 2020 at https://www.fws.gov/arcata/es/amphibians/crlf/crlf.html.

Wake, D., M. Koo, V. Vredenburg. 2020. "Amphibiaweb" (On-line). Accessed February 11, 2020 at https://amphibiaweb.org/cgi/amphib_query?where-genus=Rana&where-species=draytonii.