Predation and Disease
Known predators of mountain yellow-legged frogs include the western terrestrial garter snake (Thamnophis elegans), Brewer's blackbirds (Euphagus cyanocephalus), Clark's nutcrackers (Nucifraga columbiana), and coyotes (Canis latrans). Introduced rainbow trout (Oncorhynchus mykiss), golden trout (O. aguabonita), brook charr (Salvelinus fontinalis), and brown trout (Salmo trutta) have been observed to prey on all life stages of mountain yellow-legged frogs. Fish did not occur in much of the high elevation habitat occupied by mountain yellow-legged frogs until the late nineteenth century (Jennings 1988, Moyle 1976, Moyle et al 1996, Knapp 1996). Introduction of trout into high elevation lakes and streams has resulted in significant predation on frogs, is likely preventing re-colonization of locally depleted or extirpated populations, and has altered lake food webs and nutrient cycles
Frogs are also susceptible to mortality from diseases. Bradford (1991) observed a large-scale die-off of mountain yellow-legged frogs from red-leg disease caused by the bacterium (Aeromonas hydrophila). Recently, a chytrid fungus has been infecting larvae and subadults. Chytrid fungus damages the mouthparts of tadpoles, and then goes on to damage keratin in the skin of metamorphosed frogs, eventually killing them. Chytrid fungi are ubiquitous in soil, but the aquatic chytrid infecting frogs was discovered fairly recently.
Because many of the remaining populations of Sierra Nevada mountain yellow-legged frog are small isolated remnants, they are vulnerable to random natural events that could quickly extirpate them.
Surveys have shown that 93% of the R. sierrae and 95% of R. muscosa historical populations are now extinct. In 2003 the U.S. Fish and Wildlife Service (USFWS) determined that the Sierra Nevada population of the mountain yellow-legged frog should be protected under the Endangered Species Act, but that listing the species under the Act is "warranted but precluded". On September 15, 2010, the California Fish and Game Commission accepted a petition from the Center for Biological Diversity to list all populations of the mountain yellow-legged frog (Rana muscosa and Rana sierrae) as "endangered" under the California Endangered Species Act. On February 2, 2012, the California Fish and Game Commission voted 5-0 to add both species of the mountain yellow-legged frog to the list of animals protected under the California Endangered Species Act. The U.S. Fish and Wildlife Service will be releasing its proposed rule related to listing under the U.S. Endangered Species Act in October 2012.
Conservation efforts: High Mountain Lakes Project