Mountain Yellow-legged Frog (Northern Distinct Population Segment [DPS])

Rana muscosa

Picture of Mt Yellow-Legged Frog
Photo Credit: Ricky Kuyper/USFWS

Basic Species Information

STATUS

Endangered. This species is in danger of extinction throughout all or a significant portion of its range.

DESCRIPTION

The mountain yellow-legged frog is a medium-sized amphibian, measuring about 1.5 to 3.25 inches on average. Females tend to be slightly larger than males.

Adult frogs a mix of brown and yellow coloring on their upper (dorsal) body, but can also be grey, red, or greenish-brown, usually with dark spots or splotches, called cryptic coloration. These spots can look like lichen or moss and make the frog appear camouflaged. The belly and underside of the back legs, and sometimes the front legs, are yellow or light-orange. This gives the frog part of its common name—"yellow-legged."

If disturbed or threatened, mountain yellow-legged frogs produce a distinctive mink-or garlic-like odor to ward off predators and other animals.

Although these frogs do not have vocal sacks, they can vocalize in or out of water, making what has been described as a flat "clicking" sound.

The tadpoles reach about 2.8 inches in length and generally are mottled brown on the upper side with a faintly yellow underside.

FOOD SOURCES

This species eats a variety of terrestrial and aquatic invertebrates, including beetles, ants, bees, wasps, flies, and dragonflies. Tadpoles may also be consumed.

Frogs tend to sit and wait until they see prey come within range, or may creep up a little, before striking with their large sticky tongue to catch the prey and bring it into the mouth.

HABITAT

Mountain yellow-legged frogs are highly aquatic and are rarely found more than 3.3 feet from water. They can be found sitting on rocks along the shoreline where there may be little or no vegetation.

These species historically inhabited lakes, ponds, marshes, meadows, and streams at elevations typically ranging from about 4,500 to 12,000 feet.

HIBERNATION

Mountain yellow-legged frogs emerge shortly after snow melts to forage and so adults can breed. In years of heavy snow, they may only be active for about three months.

MATING

Reproduction is aquatic. Fertilization is external, with the male grasping the back of the female (“amplexus”) and releasing sperm as the female lays her eggs. Mating and egg-laying occurs from May to July.

Mountain yellow-legged frogs deposit their eggs in globular clumps, which are often somewhat flattened and roughly one to two inches in diameter.

Spawn size varies from 15 to 350 eggs per mass and eggs hatch in 18 to 21 days with water temperatures from 41 to 56 degrees Fahrenheit.

Tadpoles often require two to four years to reach metamorphosis (i.e., the time required to reach reproductive maturity), depending on local climate conditions and site-specific conditions. After the frogs transition from tadpoles, metamorphosis, is thought to vary between three and four years. In total, it can take five to eight years for mountain yellow-legged frogs to start reproducing after they emerge from their egg mass.

RANGE

The northern DPS of the mountain yellow-legged frog occurs only in the western Sierra Nevada and extends from south of the Monarch Divide in Fresno County through portions of the Kern River drainage.

Most of these frogs are now found on National Forest and National Park lands.

THREATS

Threats include habitat degradation and fragmentation, predation and disease, climate change, and the interaction of these various stressors impacting small remnant populations.

There has been a range-wide reduction in abundance and geographic extent of surviving populations of frogs following decades of fish stocking, habitat fragmentation, and most recently a disease epidemic. Surviving populations are smaller and more isolated, and breeding in disease-infested populations is highly reduced from historic norms. Studies show that populations of the northern DPS of mountain yellow-legged frog have declined by over 80 percent.

Fish compete with and prey upon mountain yellow-legged frogs, tadpoles, and eggs. In the past, these animals experienced natural predation, mostly by garter snakes and sometimes birds. But the scope and scale of fish stocking activities over the last century has effectively replaced mountain yellow-legged frogs from much of their native habitat, and isolated remaining populations from each other. Recently, the “chytrid” fungus (Batrachochytrium dendrobatidis) has rapidly spread through the Sierra Nevada. The fungus has decimated populations that persisted despite the continued presence of fish within their native range.

WHAT YOU CAN DO

Wherever you live in California, there are zoos and nature centers where you can see and learn about frogs. You can also download the scientific species account and read about recent efforts to combat chytrid.