Wild Populations of Endangered Frog Found in Southern California

The mountain yellow-legged frog, Rana muscosa, is on the federal Endangered Species List and is classed as Critically Endangered by the IUCN Red List of Threatened Species. Until last month researchers had estimated only 122 adult mountain yellow-legged frogs remained in the wild.

In June, two separate groups of scientists pursuing different goals each discovered mountain yellow-legged frogs in the San Jacinto Wilderness.

The frogs were spotted at two locations about 2.5 miles apart in the Tahquitz and Willow creeks in the San Jacinto Mountains. The number of frogs in the area has not yet been determined.

"If this population is large, it could play an important role in the re-establishment of this species across Southern California," said Adam Backlin, a biologist from the U.S. Geological Survey assessing suitability of sites to re-establish frogs. He led the team that on June 10 spotted the first new Tahquitz Creek frogs.

Biologists from the San Diego Natural History Museum made their find June 25. To study biological change in the region over the past 100 years, the museum scientists were retracing the path of a 1908 expedition by the Museum of Vertebrate Zoology, University of California, Berkeley. Then, the frog was collected at five sites in the San Jacinto Mountains.

The museum scientists were in the Tahquitz Valley area during the week of June 21 when field biologist Drew Stokes found and photographed a single mountain yellow-legged frog in Willow Creek, a tributary of Tahquitz Creek.

Mountain yellow-legged frog (Photo by Eugene van der Pijll, USGS)

This rediscovery is a windfall for government and nonprofit partners working to increase the number of mountain yellow-legged frogs in the wild by means of habitat protection and restoration as well as a captive breeding and release program.

In addition to the USGS and the San Diego Natural History Museum, the effort involves the San Diego Zoo's Institute for Conservation Research, the California Department of Transportation, U.S. Fish and Wildlife Service, U.S. Forest Service, University of California and California Department of Fish and Game.

The San Diego Zoo was the first to breed a mountain yellow-legged frog in captivity. That animal has recently morphed from a tadpole into juvenile frog. The goal of the program is to breed mountain yellow-legged frogs in captivity and return them to their native habitat.

"Historically, scientists have had great difficulty breeding frogs in captivity," said Jeff Lemm, an animal research coordinator for the zoo. "We are excited by this success and cautiously optimistic we will have more eggs soon."

The frog recovery effort is funded by Caltrans to compensate for emergency work to stabilize a slope near the frogs' habitat on state Route 330 in the San Bernadino Mountains.

Craig Wentworth, a senior environmental planner/biologist with Caltrans, said, "The emergency slope reconstruction project had the dual benefit of opening a road that was about to fail as well as helping to ensure that the last known population of the mountain yellow-legged frog in the San Bernardino Mountains had a program in place to aid recovery."

The California Department of Fish and Game is working towards completion of a trout removal project to benefit the endangered mountain yellow-legged frog in Little Rock Creek in the Angeles National Forest.

Trout were introduced to lakes and streams throughout the region in the late 1800s to benefit recreational fishers. However, tadpoles often become prey to non-native fish such as trout and at the tadpole stage, mountain yellow-legged frogs can take up to two years to mature, so are vulnerable to fish predation for a long period of time.

Trout populations have been reduced in one section of Little Rock Creek and as a result, frogs in that section have increased, demonstrating the success of this approach.

Jim Bartel, the field supervisor for the U.S. Fish and Wildlife Service office in Carlsbad, said his agency is pleased to participate in the effort to rescue the mountain yellow-legged frog and conserve its remaining riparian habitat. Bartel said, "We look forward to reintroducing the species to its native habitat."

Globally, frogs and other amphibians are on the decline because of habitat loss, the effects of climate change, pesticide contamination and the spread of a deadly fungus.

Copyright Environment News Service, ENS, 2009. All rights reserved.