With Easter around the cor­ner, South­ern Cal­i­for­nia biol­o­gists are play­ing bunny and hid­ing some 300 eggs in the wild.

But these are tiny, gelati­nous eggs that belong to Rana mus­cosa — the moun­tain yellow-legged frog (also know as the Sierra Madre yellow-legged frog). And the eggs went into a chilly stream in the James San Jac­into Moun­tains Reserve near Idyll­wild, Cal­i­for­nia, as part of an ongo­ing effort to pre­serve this endan­gered amphib­ian. The site is part of the Uni­ver­sity of Cal­i­for­nia Nat­ural Reserve Sys­tem, a net­work of 36 pro­tected nat­ural areas encom­pass­ing approx­i­mately 150,000 acres used for research and education.

Researchers from USGS and the San Diego Zoo released these eggs on April 14. The eggs were laid by cap­tive frogs at a zoo lab­o­ra­tory 90 miles away. The expe­di­tion was part of a larger USGS-led part­ner­ship to study the South­ern Cal­i­for­nia pop­u­la­tion of the moun­tain yellow-legged frog, which is fed­er­ally listed as endan­gered with only 200 adult frogs remain­ing in the wild.

USGS West­ern Eco­log­i­cal Research Cen­ter biol­o­gists Adam Back­lin and Liz Gal­le­gos lead the annual pop­u­la­tion mon­i­tor­ing and cap­tures of the frogs, while the San Diego Zoo, Los Ange­les Zoo and Fresno Chaf­fee Zoo man­age cap­tive breed­ing pro­grams. The U.S. Fish and Wildlife Ser­vice and Cal­i­for­nia Depart­ment of Fish and Game are respon­si­ble for the frog’s man­age­ment and recov­ery, and the Uni­ver­sity of Cal­i­for­nia Nat­ural Reserve Sys­tem pro­tects the stream they were released into.

“We’re hop­ing that we also see some matur­ing frogs from last year’s batch of released tad­poles, when we head out to release the eggs on Thurs­day,” says Back­lin, who has been prepar­ing the eggs’ new home in the 50-degrees-cold stream waters.

The eggs were placed in a cage made of win­dow screen­ing, and should hatch out tad­poles over the com­ing weeks. The cage also helps researchers count how many tad­poles actu­ally hatched, and pro­tect them for a lit­tle while before they are released to their free­dom — hope­fully to sur­vive nature’s haz­ards and grow into adult frogs that help repop­u­late this dwin­dling species.

“Researchers and man­agers know that the San Jac­into Reserve once had a yellow-legged frog pop­u­la­tion in the mid-1990’s,” says Back­lin, who is based in Irvine. “This par­tic­u­lar area is already pro­tected land, closed off from human activ­i­ties and is easy for us researchers to hike to and mon­i­tor. So it seemed a safe loca­tion to pick for a rein­tro­duc­tion effort.”

South­ern Cal­i­for­nia moun­tain yellow-legged frogs are now only found in the San Gabriel, San Bernardino and San Jac­into moun­tains. A group of San Gabriels frogs were res­cued after the 2009 Sta­tion Fire, and those are cur­rently being cared for at the Fresno Chaf­fee Zoo.

Mean­while, the Los Ange­les Zoo also has a group of San Jac­into frogs, whose lat­est batch of 500 eggs will be hatched into tad­poles in prepa­ra­tion for a June release.

This project is one of many efforts under the USGS Amphib­ian Research and Mon­i­tor­ing Ini­tia­tive, which was char­tered by con­gres­sional man­date to study the trou­bling amphib­ian declines in the U.S. and around the world.

– Ben Young Lan­dis, USGS

See more pho­tos of the release at the USGS West­ern Eco­log­i­cal Research Center.