NATURAL HISTORY

SIERRA NEVADA MOUNTAIN YELLOW-LEGGED FROG } Rana muscosa
FAMILY: Ranidae

DESCRIPTION: The Sierra Nevada mountain yellow-legged frog is of moderate size with highly variable color, ranging from brown and yellow to gray, red, or green-brown, with patterns of dark spots or patches on the back. The underside of the hind limbs can vary from a pale-lemon color to bright sun yellow. Eyes have an intense gold iris with a horizontal black counter-shading stripe. Females are slightly larger than males, up to three inches long.

HABITAT: Mountain yellow-legged frogs live in glaciated alpine lakes, ponds, tarns, springs, and streams. Lakes used usually have grassy or muddy margins, and adults are typically found sitting on wet rocks along the shoreline, usually where there is little or no vegetation.

RANGE: The frog lives in the Sierra Nevada Mountains of California and Nevada from southern Plumas County to southern Tulare County, at elevations mostly above 6,000 feet. A genetic study published in 2007 revealed that there are two distinct mountain yellow-legged frog species that do not overlap in range or interbreed: a northern and central Sierra Nevada species and a southern Sierra Nevada and southern California species.

MIGRATION: This species has no distinct breeding migration, as adults are almost always found within two to three feet of water. In some areas, there is a seasonal movement of frogs from deeper lakes to nearby breeding areas after overwintering. Frogs typically move less than a few hundred meters.

BREEDING: Breeding sites are generally located in, or connected to, lakes and ponds that do not dry up in the summer, and that are sufficiently deep not to freeze through in winter. Since larvae are susceptible to fish predation, successful breeding sites do not overlap with fish presence. The frogs breed in June or July.

LIFE CYCLE: Eggs hatch within several weeks and larvae usually transform during July or August. Larvae at high elevations or subject to severe winters may not metamorphose until the end of their fourth summer. Adults hibernate in water during the coldest months, under ice or near shore under ledges and in underwater crevasses.

FEEDING: Adults feed on terrestrial insects and adult aquatic insects: beetles, flies, wasps, bees, ants, true bugs, and spiders. They also consume large quantities of Yosemite toad and Pacific treefrog tadpoles and can be cannibalistic. Tadpoles graze on algae and diatoms along rocky bottoms of streams, lakes, and ponds.

THREATS: These frogs are threatened by predation by introduced trout, pesticides, environmental changes from drought and global warming, disease, and habitat degradation due to livestock grazing.

POPULATION TREND: More than 93 percent of northern and central Sierra Nevada populations, and more than 95 percent of southern Sierra Nevada and southern California populations, are already extinct.