Conservation and recovery of the mountain yellow-legged frog in Southern California, USA

Summary

The mountain yellow-legged frog (Rana muscosa), Endangered and reduced to nine known populations totaling fewer than 200 adults across southern California's Transverse Ranges after losing over 98% of its historic range, is managed by a multi-agency working group formed in 1999 including USGS, US Fish and Wildlife Service, and three zoos, all populations testing positive for the chytrid fungus Bd. Emergency tadpole rescues, 86 individuals from a drying pool in 2006 and 106 more after a 2009 wildfire, seeded captive breeding colonies at the San Diego Zoo and Fresno Chaffee Zoo, which after securing multi-agency permits and a formal interagency agreement achieved the species' first successful captive breeding in 2010, producing about 1,200 eggs. Two 2010 releases into Indian Creek, Riverside County placed three egg masses (about 600 eggs) in stream cages in April and 36 head-started tadpoles in August, but only 46 of the released eggs proved fertilized and no hatched tadpoles were ever detected in the creek, likely due to their small size and cryptic behavior, leaving just the 36 head-started tadpoles as the year's confirmed release total of 80 frogs. Major difficulties included the complex multi-agency permitting process, securing long-term funding, and low fertility in the first captive breeding attempt. The project rates itself Partially Successful, framing the achievement of successfully releasing a captive-bred endangered species as the year's core accomplishment while acknowledging that evaluating whether the new population actually establishes will take at least five more years.