Mountain Yellow-legged Frog (Rana muscosa) Fact Sheet: Behavior & Ecology

Daily activity

• Diurnal

Seasonal activity

• Migrate to suitable areas for reproduction, feeding, and over-wintering
• Hibernation
• Sierra Nevadas (Bradford 1984)
• Hibernate underwater in lakes and streams
• 6 to 9 months prior to the spring breeding season
• Southern California
• May hibernate in deep stream pools for up to 6 months (Santana 2015)
• Active after snow melts and before winter freeze (Mathews and Pope 1999)
• Both tadpoles and adults seek warmest thermal regions
• Never far from water

Females

• Average range of 462 yards² (386 m²) in August
• Average range of 6098 yards² (5,099 m²) in September

Males

• Male territory is much smaller
• Between 87 and 98 yards² (73 and 82 m²)

Very aquatic frog species

• Tadpoles hide under rocks and mud in ponds and lakes
• Tadpoles obtain oxygen through skin, gills, and mouth
• Underwater, adult frogs obtain oxygen through skin and mouth
• Occupy shallow depressions at bottom of frozen lakes in winter
• When threatened, will bury in substrate

Dormancy

• Metabolic rate decreases significantly during dormancy
• High mortality can occur with oxygen depletion (lakes that are frozen over contain less oxygen)
• Tadpoles move to warmer waters in spring
• Increases body temperature and metabolic rate, hastening development
• Rising temperatures determine end of dormancy

Ectothermic

• Like all amphibians, Rana muscosa is ectothermic or "cold-bodied" (external environment regulates body temperature)
• Not usually in shade for longer than 20 minutes
• Bask in sun to achieve high body temperatures
• Body temperature is about 25°F warmer while basking in sun (vs. in shade)
• Find warm micro-habitats next to shoreline
• Move back and forth from water

Call is a short, raspy croak or clicking sound

• Can call underwater
• Audio recording

Only male frogs make courtship calls

• Call to attract a mate
• Call to communicate to female that she is about to be mounted
• Warning call to males
• If about to be grasped by another male

Vocalize to defend territory

Calls made through vibration of vocal cords, as frog exhales

• No vocal sacs present to further modify sounds (as in other frog species)

Migration to over-wintering habitat

• Frogs move in short bursts of 2-5 hops (Mathews and Pope 1999)
• Appear to rest between bursts
• Fairly straight routes
• Use shortest distance over dry land

Jumping

• Forelimbs lift up, hind legs extend
• Propels frog into the air, as hind feet roll off ground
• Propelled at approximately a 45° angle
• Forelimbs brace frog as it lands

Swimming

• Hind legs extend backwards causing webbed toes to open
• Webbing increases surface area of foot
• Allows frog to use water as a launching pad
• Frog is propelled upwards and forwards
• Forelimbs held flat against body as frog swims

Predators of tadpoles

• Trout: brown, golden, rainbow
• Also eat eggs (Natalie Calatayud, personal communication, 2016)
• Brook char

Predators of adults

• Garter snakes
• Brewer's Black Bird
• Clark's Nutcracker (bird)
• Raccoons
• Coyotes

Tadpole coloration provides excellent camouflage with leaf litter found at the bottom of creeks.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.