The southern mountain yellow-legged frog is highly variable in coloration. They may be brown, yellow, grey or greenish-brown across the back with black or brown mottling. On the throat the skin is white or yellow with brown mottling. The underside of the body is a faint yellow and the underside of the leg is yellow or orange.
Their eye is gold with a horizontal, black pupil.
Females tend to be larger than males. An average southern mountain yellow-legged frog is 4-8.9cm (1.6-3.5in) long. Animals found at higher elevations tend to be smaller. Males weigh 21g (0.74oz) while females weigh 33g (1.16oz).
Southern mountain yellow-legged frogs are carnivores in their adult form. They eat a range of invertebrates both on the land and in the water. Tadpoles are also consumed.
As a tadpole they will feed primarily on diatoms and algae though this is supplemented with small insects.
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North America is the native home of the southern mountain yellow-legged frog. Here they are confined to southern California in a trio of mountain ranges. They are considered extinct across large parts of their former range.
They live at altitudes between 1,066 and 3,658m (3,500 and 12,000ft).
Much of their current range is restricted to National forests and parks.
They make their home in mountain streams and banks with suitable vegetation on the banks as well as lakes, ponds and marshes.
Breeding occurs from May to July. A male will grab on to the back of the female in a position called amplexus. She then lays her eggs and he fertilizes them as she does this.
A females egg mass can contain anywhere from 15-350 eggs. These are laid in globular clumps which are somewhat flattened.
These eggs will take 18-21 days to hatch and emerge as tadpoles who are confined to the water. These tadpoles may measure up to 7.62cm (3in) long. As a tadpole they have gills to breathe in the water.
The time between hatching and metamorphosis is variable between elevations. At lower elevations it can happen in the same season but at higher elevations it may take as many as four years.
During their metamorphosis they will lose the gills and develop lungs. The tail will shorten and be reabsorbed.
It may take between 5 and 8 years for sexual maturity to be reached in the wild.
Mountain yellow frogs will hibernate over winter. In some areas they may only be active for three months of the year. Hibernation occurs underwater in lakes and rivers.
These frogs lack a vocal sac though they do make what is described as a flat ‘clicking’ sound. Males make a call to attract a mate.
They are active during the day. During the day they will bask in the sun to warm up their body.
Predators and Threats
If threatened by a predator the mountain yellow-legged frog will emit a foul smelling odor (similar to garlic) in an attempt to ward them off.
Humans present a range of challenges to the survival of the southern mountain yellow-legged frog. These include habitat destruction and fragmentation, climate change and diseases such as chytrid fungus.
Due to the low population some instances of inbreeding have occurred and led to a decrease in genetic diversity.
A range of captive breeding programs exist which are working to release mountain yellow-legged frogs to the wild.
They are among the largest frogs found in North America.
As few as 200 mountain-yellow legged frogs are estimated to remain in the wild.
USFWS/Rick Kuyper / CC BY (https://creativecommons.org/licenses/by/2.0)
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By Pacific Southwest Region USFWS from Sacramento, US – Mountain yellow-legged frogs after release, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=54948893
Mountain Yellow-Legged Frog (Rana muscosa) Fact Sheet. c2016. San Diego (CA): San Diego Zoo Global; [accessed 2020 09 07]. http://ielc.libguides.com/sdzg/factsheets/ mountainyellow-leggedfrog
Davison, V., 2020. Mountain Yellow-Legged Frog – Amphibians And Reptiles, Endangered Species Accounts | Sacramento Fish & Wildlife Office. [online] Sacramento Fish and Wildlife. Available at: <https://www.fws.gov/sacramento/es_species/Accounts/Amphibians-Reptiles/mt_yellow_legged_frog/> [Accessed 7 September 2020].
AmphibiaWeb 2018 Rana muscosa: Southern Mountain Yellow-legged Frog <http://amphibiaweb.org/species/5104> University of California, Berkeley, CA, USA. Accessed Sep 5, 2020.
Californiaherps.com. 2020. Southern Mountain Yellow-Legged Frog – Rana Muscosa. [online] Available at: <http://www.californiaherps.com/frogs/pages/r.muscosa.html> [Accessed 7 September 2020].
Geoffrey Hammerson. 2008. Rana muscosa. The IUCN Red List of Threatened Species 2008: e.T19177A8847938. https://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T19177A8847938.en. Downloaded on 07 September 2020.