SAN DIEGO — Efforts to save the mountain yellow-legged frog -- the sweet-croaking amphibian that once roamed Southern California forests but is now on the endangered list -- have suffered a setback.
All seven of the tiny frogs that were part of a rescue effort by the San Diego Zoo have died mysteriously, officials announced Tuesday.
The frogs were found in late 2003 in a shallow pool near the City Creek area of the San Bernardino Mountains soon after the state's largest brush fire had roared through the area.
Of all the animal and plant species hit by the firestorm, the mountain yellow-legged frog, Rana muscosa, was among the hardest hit as its already shrinking habitat was destroyed.
Researchers had hoped that the seven rescued frogs -- one female and six males -- could provide enough offspring to start a colony. They were being watched and fattened up on crickets by the Conservation and Research for Endangered Species program that is attached to the zoo's Wild Animal Park.
The female was the first to go. The males followed over a period of days. Efforts to boost their strength by giving them "calcium baths" proved futile. The frogs were being kept in plastic dishes, waiting for the day when they could be transferred to special terrariums.
"They just never got to the point where they could get into their tanks," zoo spokesman Andrew Circo said.
Necropsies have been ordered to determine the cause of death. Initial results show that the seven suffered from a bacterium that is a distant cousin to tuberculosis.
Researchers had been buoyed several weeks ago when the frogs were declared free of a fungus, Batrachochytrium dendrobatidis, that is wiping out frog populations worldwide. All seven had the fungus when they arrived in San Diego from the Los Angeles Zoo.
But Circo said the knowledge that researchers gained in successfully treating the frogs for the fungus may prove helpful as they continue the hunt for a cure for frogs in the wild.
The zoo will continue working with state and federal agencies on a yellow-legged frog rescue program, Circo said.