The Latin name of the frog species is Rana muscosa. Their food consists of insects, eggs, tadpoles and even other frogs. Frogs are important for the ecological balance in an ecosystem. They keep the insect population down.

Rana muscosa is endemic to California, USA. The yellow-legged frog from Southern Mountain once stretched from Palomar Mountain in San Diego County through the San Jacinto, San Bernardino and San Gabriel Mountains in Riverside, San Bernardino and Los Angeles counties in Southern California.

The adult Mountain yellow-legged frog lives mainly on insects found on land and also the aquatic insects that seek out on the beach and live in shallower water. Tadpoles live on algae along rocky lake bottoms and other watercourses.

Highly Endangered

The Mountain yellow-legged frog is highly endangered. The goal is to try to multiply the frogs in captivity in order to then be able to reintroduce them into the wild.

Chytrid fungus

The Mountain yellow-legged frog are highly susceptible to a chytrid fungus known as “Bd” that is sickening millions of frogs worldwide. To treat frogs exposed to Bd, biologists build large, 180*180 cm net pens to hold the frogs in and the caught as many frogs as possible to keep in these pens. Treating a sufficient number of frogs in the population can prevent local extinction.

The Mountain yellow-legged frogs get to soak in an antifungal treatment solution for approximately 10 minutes once a day for eight days. The treatment reduces the amount of fungus on the frogs’ skin, allowing their immune systems to catch up and begin to fight the fungus naturally. There are also indications that raised water temperature can help treat Chytrid fungus in MYLF.

Mountain’s yellow-legged frog complex

This frog is one of the two species within the mountain’s yellow-legged frog complex. The two species are Rana muscosa and Rana sierrae. Both species need water to survive and go no further than a meter or two from the water’s edge.

Both Rana sierrae and Rana muscosa are yellowish in the skin. From above, they are reddish brown and have black or brown spots marked. The tips of the toes are dark. The entire underside of the frog is yellow or light orange. Another similar species is the Foothill Yellow legged frog, which is more transparent than the Mountain yellow-legged frog. The yellow colour extends towards the forelegs. Dorsolateral folds are usually present, but they can often be quite indistinct.

Identify MYL frog
The upper picture displays a Mountain Yellow-legged frog. The lower picture is a Foothill yellow-legged frog


As soon as the snow melts, the frog departs from its winter habitat. Its mating period commences after the most severe meltwater flow has ended, typically between March and May in the southern regions of its range. This period can extend until July in the northern, higher altitude regions. The eggs are fertilized externally, with the cluster secured to aquatic plants in a moving stream, or occasionally left to float freely in calm waters.

The onset of the breeding season can fluctuate between 1-4 years, and snow levels and ambient temperatures heavily influence this timing. Extremely low temperatures have the potential to kill the larvae. The young frog, or tadpole, may remain in this state for a period of 3 to 4 years before it starts to transform.

However, this duration can significantly vary depending on the environmental temperature and altitude. There are two categories of tadpoles: those in their first year, and those in their second year. Typically, the transformation from tadpole to young frog, a phase known as metamorphosis, occurs in the second summer of the tadpole’s life.

When the metamorphosis phase is underway, they are referred to as metamorphs. Once they have survived their first winter, they are then classified as juveniles. After two years in the juvenile stage, they reach sexual maturity and are ready to reproduce. Interestingly, it has been noted that the growth and development rates tend to slow down at higher elevations.

Rana muscosa or Rana sierrae

What distinguishes the two species Rana muscosa and Rana sierrae is that the Mountain yellow-legged frog (Rana muscosa) has longer legs. When the leg is folded towards the body, the tibiotarsal joint usually extends beyond the outer veins. Mating calls also separate the two species. Rana muscosa’s mating calls lack transitions between pulsed and noted sounds. Both species use their mating calls underwater. The males can also be heard above the water surface, but only if you are close, no more than two meters away.


The Mountain Yellow-Legged Frog is considered an endangered species under the US Endangered Species Act. Its population is divided into two distinct segments (DPS): the northern DPS, which has been listed as endangered since 2014, and the southern DPS, declared endangered in 2002. The Tehachapi Mountains form a geographical divide between these two segments, and they each inhabit different environments. The northern DPS resides in lakes or slow-moving water bodies at alpine and subalpine elevations in the Sierra Nevada, whereas the southern DPS inhabits the quicker and warmer waters of the chaparral, occasionally being found at higher elevations in the Transverse Range. Furthermore, these two DPS show genetic divergence, indicative of their long-term reproductive isolation.

International conservation organizations have also recognized the perilous status of the Mountain Yellow-Legged Frog. The International Union for Conservation of Nature lists it as endangered, while its conservation status on NatureServe is “critically imperiled.”

The San Diego Zoo marked a conservation milestone in 2009, when it achieved the first successful captive breeding of the frog. The zoo raised three tadpoles, and its conservation team intends to release any additional captive-bred frogs into their native range, the San Jacinto Mountains.

Efforts to reintroduce the species to their natural habitats have been ongoing. In 2015, frogs and tadpoles of the species were reintroduced to Fuller Mill Creek in the San Bernardino Mountains and San Bernardino National Forest. They were bred and raised at the Arnold and Mabel Beckman Center for Conservation Research in Escondido, which collaborates with the San Diego Zoo Institute for Conservation Research (ICR) to prevent the species from becoming extinct. The Los Angeles Zoo, another coalition partner, is raising two groups of tadpoles from different localities in the San Gabriel Mountains for future release.

Meanwhile, the Oakland Zoo initiated a rehabilitation project for the frog in 2015. Each year, a group of tadpoles are collected from native lakes across California and brought to the zoo. These tadpoles are nurtured to juvenile frog stage and inoculated against the chytridiomycosis fungus disease. Once immune and ready, these frogs are released back into the lakes where they were originally found. In 2016, the zoo released 53 specimens into various lakes in the Sequoia and Kings Canyon National Parks. The program planned to release 130 inoculated individuals into lakes in these National Parks and the Inyo National Forest in 2017.

In response to recent wildfires that adversely affected the habitats of these frogs, the Aquarium of the Pacific partnered with governmental organizations like the California Department of Fish and Wildlife in 2021. Their collaboration led to the creation of a facility dedicated to the care and conservation of Mountain Yellow-Legged Frogs. Wildlife agencies have rescued and relocated frogs from fire-damaged habitats to this facility. Such efforts aid in the recovery of the species after natural disasters and stave off their extinction.