Mountain Yellow-legged Frog (Rana muscosa) Fact Sheet: Population & Conservation Status

IUCN Status

• Red List
  • Endangered (2021 assessment) (IUCN SSC Amphibian Specialist Group 2022)
• Green List
  • Largely Depleted (2024 assessment) (Sheir et al. 2024)
    • Conservation breeding and reintroduction efforts helping MYLF populations survive chytrid fungus, habitat loss, drought, and introduced predators

CITES Status

• Not listed (UNEP 2019)

United States Endangered Species Act

• Endangered

California

• Endangered

 History of Conservation Efforts

• Identification of two distinct populations: northern and southern California
  • 2002: Given Endangered Species Status by USFWS
  • 2006: Designation of Critical Habitat by USFWS; 8,283 acres in portions of Los Angeles, Riverside, and San Bernardino counties
  • 1996-2004: Listed as Vulnerable by IUCN
  • 2006: Listed as Critically Endangered by IUCN
  • 2008: Listed as Endangered by IUCN

By 2003, fewer than 200 individuals remained in the wild

• Survey of 150 historical distribution sites (Backlin 2013)
  • Nine small populations were detected
  • Abundance estimates were small (1–55 adults per population).
  • Data indicated most of the remaining populations had fewer than 10 pairs of adults.
• Reintroductions of individuals bred in managed care supplementing reproduction in wild populations

San Diego Zoo Wildlife Alliance

• Leading efforts to study the reproduction and natural history of this species, with ultimate goal of preventing its extinction
• Hatch eggs and raise young frogs in managed care
  • Release into the wild
• Working to improve husbandry and managed care breeding protocols
  • Simulate seasonal temperature changes (hibernation cues)
  • Simulate natural light cycles
  • Study nutritional requirements
• Use assisted reproduction techniques (e.g., hormone therapies and in vitro fertilization)
• Partnerships with the California Department of Fish and Wildlife, U.S. Forest Service, U.S. Fish and Wildlife Service, U.S. Department of Agriculture, U.S. Geological Survey, Los Angeles Zoo, and Omaha’s Henry Doorly Zoo and Aquarium
• Preserving genes in The Frozen Zoo®
• Studying embryo and tadpole development
• See Managed Care

(Hammerson 2008)

Diseases

• Chytrid fungus
• Red-leg disease/syndrome

Predation

• Predation on tadpoles by non-native fish
  • Especially introduced trout

Environmental effects

• Drought
• Fire (SDZWA Press Releases)
  • Habitat saturated in ash and debris
• Loss of genetic vigor due to population isolation and inbreeding
• Air and water contamination
  • Agricultural chemicals/pesticides
  • Low pH and elevated aluminum concentrations
  • Mining
  • Human disturbance of wildlife areas
• Threats described by IUCN (International Union for Conservation of Nature)

Learn how San Diego Zoo Wildlife Alliance researchers raise endangered mountain yellow-legged froglets for reintroduction into the wild.

© San Diego Zoo Wildlife Alliance. All rights reserved.

SDZWA Senior Research Coordinator, Jeff Lemm, checks a clutch of Mountain Yellow-Legged Frog eggs.

San Diego Zoo Wildlife Alliance has been breeding, raising and reintroducing frogs into historical native habitat since 2010.

Image credit: Ken Bohn, © San Diego Zoo Wildlife Alliance. All rights reserved.

 

Release into Fuller Mill Creek.

Image credit: Ken Bohn, © San Diego Zoo Wildlife Alliance. All rights reserved.

USFWS (2002)
USFWS (2006)
IUCN (2004)
IUCN (2006)
IUCN (2008)
Backlin (2013)
Fellers et al. (2001)
Vredenburg et al. (2008)