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Foothill Yellow-legged Frog

Rana boylii

What do they look like?

The backs of foothill yellow-legged frogs are colored like the ground, so they can be almost black, dark brown, reddish brown, gray, olive, or greenish with spots and speckles. Some have a light spot within a dark area on their upper eyelid. Their underside is white or light yellow, and more yellow at the back of the body and back legs. They have a wide, pointy head. The bones between their knees and ankles are extra long, about half the length of the body. Their back feet are short and completely webbed. Foothill yellow-legged frogs are 3.8 to 8.1 cm long. Females are bigger than males, and they are 20 to 25 mm longer. ("Amphibians of Western North America", 1951; "Handbook of Frogs and Toads of the United States and Canada", 1995; Ashton, 1997; Leonard, et al., 1993; Stebbins, 2003)

Tadpoles are olive or olive-gray on top, and have dark brown spots on the tail and fins. They can get up to 5 cm long before they transform into frogs. ("Amphibians of Western North America", 1951; Stebbins, 2003)

  • Sexual Dimorphism
  • female larger
  • Range length
    5 to 9 cm
    1.97 to 3.54 in

Where do they live?

Foothill yellow-legged frogs used to live west of the Cascade mountains from Oregon to California, where they were one of the most common amphibians. Now, they only live in some parts of this area. For example, they no longer live in the San Gabriel Mountains or the coast of Monterey County in California. Only a few of them still live around the base of the southern Sierra Nevada Mountains. ("AmphibiaWeb", 2010; "California Reptiles and Amphibians", 2010; "Encyclopedia of Life", 2010; Ashton, 1997; Leonard, et al., 1993; Stebbins, 2003)

What kind of habitat do they need?

Foothill yellow-legged frogs are almost always in the water. They live in streams, springs, and freshwater lakes, and prefer creeks with rocky bottoms. They usually live in gently flowing water. They prefer to lay eggs in creeks or streams with water that flows softly. Adults spend most of their time sitting on rocks in the stream or nearby on the banks. If they are startled, they immediately leap into the water and quickly swim to the bottom. In clear water, they take shelter under overhanging rocks. In streams with muddy bottoms, they stir up the silt on the bottom and hide in the mud. They live at sea level and anywhere up to 2,040 m in elevation. ("Amphibians of Western North America", 1951; "Handbook of Frogs and Toads of the United States and Canada", 1995; Leonard, et al., 1993)

  • Aquatic Biomes
  • rivers and streams
  • temporary pools
  • Range elevation
    sea level to 2,040 m
    to ft

How do they grow?

Foothill yellow-legged frog eggs develop for 5 to 37 days before they hatch into tadpoles. Then, the tadpoles stay close to the egg mass for about 1 week. Their head and body can be up to 18 mm long, and their tail can be up to 29 mm long. They usually transform into frogs within 3 to 4 months, but this can change with how warm the water is or how much food is available. When they transform, their tail becomes part of their body, they develop front legs, and their digestive tract changes its organization. This is just like other frogs. ("AmphibiaWeb", 2010; "Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010; Ashton, 1997; Leonard, et al., 1993)

How do they reproduce?

In March or April, male foothill yellow-legged frogs group together in the river and pick out spots where they sit and call to females. They wait until the river stops flowing so quickly after the snow melts. Females arrive later at different times, when the air and water are warmer. They only move a short ways along the stream, and often come back to the same place to breed. The calls are faint, short, grating notes followed by a rattling sound. Then, females lay eggs on the same spot males originally picked out. Males breed with more than one female in the same year. ("AmphibiaWeb", 2010; "Amphibians of Western North America", 1951; "Handbook of Frogs and Toads of the United States and Canada", 1995; "Mating strategy and breeding patterns of the foothill yellow-legged frog (Rana boylii)", 2008; Ashton, 1997; Leonard, et al., 1993)

Foothill yellow-legged frogs wait to breed until the conditions are right in their environment. At lower elevations, they breed from late March to early May, when the streams aren't as powerful. At higher elevations, they breed from June to August, after the ice and snow melts from mountain lakes. They mate and lay eggs only in streams and rivers, while other frogs that live nearby also do this in ponds and lakes. Their eggs are small clusters like grapes that are normally attached to rocks or even plants under the water. The eggs have 3 jelly envelopes, and are often black on top, and white or light gray tan underneath. Each cluster of eggs is made up of 100 to 1,000 eggs, and 900 on average. They often cover the mass of eggs with a layer of sand or silt to camouflage them from predators. ("AmphibiaWeb", 2010; "Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010; "Encyclopedia of Life", 2010; "Handbook of Frogs and Toads of the United States and Canada", 1995; Ashton, 1997)

The eggs hatch in 5 to 37 days. They probably hatch faster when the water is warmer, and slower when it is colder. They transform into frogs when they are 3 or 4 months old. Males are able to have their own young when they are 1 to 2 years old and females when they are 2 years old. ("AmphibiaWeb", 2010; "Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010; "Encyclopedia of Life", 2010; "Handbook of Frogs and Toads of the United States and Canada", 1995; Ashton, 1997)

  • How often does reproduction occur?
    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
  • 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

Females make sure that the masses of eggs they lay are attached to the rocks on the bottom of a river or stream where the water moves slowly. They cover the eggs with silt or sand to hide them from predators. Besides this, they don't invest time or energy into their young. ("California Reptiles and Amphibians", 2010; "Encyclopedia of Life", 2010)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

How long do they live?

Scientists haven't determined the lifespan of foothill yellow-legged frogs. They might be able to live for 12 years or longer like their close relatives. ("AmphibiaWeb", 2010; Ashton, 1997)

There are many threats to how long foothill yellow-legged frogs live. They can be eaten by predators or infected with parasitic helminth worms. When it's dry, they are more likely to come on land. This means they are more likely to get eaten or have their eggs dry out. Flooding can make their eggs come off the rock they're stuck to, so they are less likely to survive. They are also affected by habitat loss, pesticides, new fish species, and competition with American bullfrogs. ("AmphibiaWeb", 2010; "California Reptiles and Amphibians", 2010; Ashton, 1997)

  • Range lifespan
    Status: wild
    3 (high) years

How do they behave?

Foothill yellow-legged frogs are typically active during the day, but they are very shy. They bask in the sun on rocks or along the shore, but quickly jump into the water if they get frightened. They can leap a long distance if their hiding place is hard to get to. They usually stay in the same spot, except that they will travel hundreds of meters to breeding sites. In warmer climates, they are active year-round. In colder climates, they hibernate in cold winters. Foothill yellow-legged frogs can change from a dark to lighter color within about half an hour. They give off an oily, garlicky smell when humans touch them. ("Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010; "The Frog Book", 1913; Leonard, et al., 1993)

Home Range

Scientists don't know the size of the territory where foothill yellow-legged frogs usually live and travel. ("AmphibiaWeb", 2010)

How do they communicate with each other?

Like most other frogs, foothill yellow-legged frogs have a pair of small organs they use to make noise called vocal sacs. Their call is faint and not heard very often. In the mating season, they actually make most of their calls underwater because the stream makes it really noisy above the water. Foothill yellow-legged frogs make low-pitched and raspy sounds that are croaks, grunts or oinks. ("Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010)

What do they eat?

Foothill yellow-legged frogs eat mostly insects, and their main source of food is arthropods. They often eat spiders, beetles, "true" bugs, and flies. They also eat grasshoppers, hornets, carpenter ants, water snails, small moths, water striders, and stoneflies. They spot prey with their eyes and catch food on their big, sticky tongue. Tadpoles eat only plants at first, including different kinds of algae. They get food off the surface of plants rocks. ("AmphibiaWeb", 2010; "Amphibians of Western North America", 1951; "California Reptiles and Amphibians", 2010)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • Plant Foods
  • algae

What eats them and how do they avoid being eaten?

Foothill yellow-legged frogs are eaten by different kinds of animals as eggs, tadpoles, and grown frogs. Rough skinned newts and sunfishes like green sunfish eat their eggs and larvae. Sacramento squawfish eat egg masses, tadpoles, and adult frogs. Tadpoles are also food sources for insects like diving beetles, water bugs, and water scorpions. Herons, some songbirds, and raccoons eat tadpoles and adult frogs. Garter snakes eat tadpoles and grown frogs. Some of them, like common garter snakes, terrestrial garter snakes, and Sierra garter snakes mostly eat young frogs, and others like Oregon aquatic garter snakes prefer to eat tadpoles. They often compete with American bullfrogs for food and space, and these animals eat them as well. ("AmphibiaWeb", 2010; Ashton, 1997; Leonard, et al., 1993)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Foothill yellow-legged frogs reduce the numbers of insects that they eat. They are a food source for many predators. Tadpoles limit how much algae grows because they eat so much of it. They are sensitive to pollution and other changes in their environment, so they can serve as an early warning about problems in their environment. Foothill yellow-legged frogs get different kinds of parasitic worms in their bodies. (Ashton, 1997; Chanson and Boucher, 2004; Leonard, et al., 1993)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • helminth woms

Do they cause problems?

There are no known negative impacts of foothill yellow-legged frogs on humans.

How do they interact with us?

Like most amphibians, foothill yellow-legged frogs are sensitive to problems in their environment. This means they are an excellent species to warn conservationists about problems in their habitat. This is because their skin allows pollutants to get inside their bodies. Foothill yellow-legged frogs also eat a lot of insects, and some of these are pests to humans. (Ashton, 1997; Chanson and Boucher, 2004)

Are they endangered?

Foothill yellow-legged frogs are listed as "Near Threatened" by the IUCN Red List. They are also listed as a California Species of Special Concern, according to the California Department of Fish and Game. They are affected by erosion, competition with American bullfrogs, loss of habitat, pesticides, logging, and mining. They are sensitive to changes in stream flow, water temperature, and the amount of sediment on the stream bottom. Some groups of them live in protected lands like national forests, parks, and land owned by conservation organizations. ("AmphibiaWeb", 2010; Fellers, 2010)


Samantha Aliah (author), Michigan State University, James Harding (editor), Michigan State University, Rachelle Sterling (editor), Special Projects, Catherine Kent (editor), Special Projects.


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.

1913. The Frog Book. Garden City New York: Doubleday, Page & Company.

2010. "AmphibiaWeb" (On-line). Accessed November 19, 2010 at

2010. "California Reptiles and Amphibians" (On-line). Accessed November 19, 2010 at

2010. "Encyclopedia of Life" (On-line). Accessed November 20, 2010 at

2008. Mating strategy and breeding patterns of the foothill yellow-legged frog (Rana boylii). Herpetological Conservation and Biology, 3(2): 128-142.

Ashton, D. 1997. "FOOTHILL YELLOW-LEGGED FROG (Rana boylii) Natural History" (On-line). Accessed November 20, 2010 at

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

Fellers, G. 2010. "IUCN Red List of Threatened Species: Rana Boylii" (On-line). IUCN Red List of Threatened Species. Accessed November 22, 2010 at

Leonard, W., H. Brown, L. Jones, K. McAllister, R. Storm. 1993. Amphibians of Washington and Oregon. Seattle, WA: Seattle Audubon Society.

Stebbins, R. 2003. A Field Guide to Western Reptiles and Amphibians. New York, NY: Houghton Mifflin.

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.

University of Michigan Museum of ZoologyNational Science Foundation

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Aliah, S. 2012. "Rana boylii" (On-line), Animal Diversity Web. Accessed July 30, 2014 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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