Giving Frog Species a Leg Up for Survival

Of the animal species hit by the firestorm that roared through Southern California in the fall of 2003, the mountain yellow-legged frog was among the most devastated.

Already on the endangered list, the yellow-legged population in the San Bernardino Mountains is thought to have been nearly wiped out by the fire, increasing the chances that Rana muscosa may soon go extinct like so many amphibian species have done.

But a venture between the Los Angeles Zoo and the San Diego Zoo’s Conservation and Research for Endangered Species program, in cooperation with state and federal wildlife agencies, aims to give the smallish frog a fighting chance at a comeback. (A good-size male is about 3 1/2 inches long, or about the width of two columns of the type on this page.)

In small, closely watched tanks at the San Diego Zoo’s Wild Animal Park, seven frogs are being fattened on a diet of crickets so they can produce enough frogs to possibly start a new colony in the City Creek area of the San Bernardinos.

It won’t be easy or fast. Of the seven, only one is a female. Maintenance is also a chore. As skin-breathers, the frogs are vulnerable to any changes in their aquatic digs.

“Amphibians are a lot more difficult to maintain than a snake, lizard or another herp,” said frog project leader Jeffrey Lemm, one of the San Diego Zoo’s herpetologists.

It’s more than just a science-for-science’s-sake project. Mountain homeowners who returned after the fire missed the yellow-legged’s distinctive call and their usefulness in keeping down the mosquito population.

The decades have not been kind to the yellow-legged frog. Once it roamed -- well, hopped -- through a wide swath of the mountainous region of Southern California.

But its numbers have been greatly diminished by a variety of threats, among them: toxins, hungry bullfrogs, hungry fish, pesticides, disease and loss of habitat due to development.

Before the fire, only a couple of hundred yellow-leggeds were thought to exist in Southern California -- scattered in the San Bernardino, San Jacinto and San Gabriel mountains -- with the largest population in the City Creek area. A once-thriving population on Palomar Mountain has been extinct for a generation.

A cousin species to the Southern California yellow-legged lives in the Sierra Nevada and also is imperiled.

Amphibians are considered the miner’s canary of world wildlife -- the first to die from a change in the environment that later strikes larger creatures.

Jane Hendron, an official with the Carlsbad office of the U.S. Fish and Wildlife Service, the lead agency in enforcing the Endangered Species Act, said the decline of frogs in an area often can signal changes in the environment “that we, as humans, should become concerned about.”

That the seven frogs here survived at all involves some luck. Researchers from the U.S. Geological Survey spotted them as morphs -- the stage between tadpole and frog -- in a shallow pool near City Creek not long after the fire.

Figuring the small animals might not survive the winter, the researchers got federal and state approval to evacuate them to the Los Angeles Zoo.

It was a good move, because the mud and ash that lingered in the fire-stricken areas were deadly to many animals that had survived the flames.

“Amphibians took it badly because of all the ash that washed into the water,” Lemm said.

(In all, 11 morphs were rescued; four of them died later.)

Even in a pristine world, frogs have it tough.

“Mortality is very high,” said Russ Smith, curator of reptiles at the Los Angeles Zoo. “You start with thousands of eggs to get hundreds of tadpoles and then, after a winter, you’re lucky to have 10 frogs.”

The remaining yellow-leggeds in the wild also are being attacked by a fatal fungus -- Batrachochytrium dendrobatidis -- that is devastating frog populations worldwide.

Scientists think the fungus has existed for decades but burst out in a lethal form, in Southern California and elsewhere, more recently.

Ed Auer, ranch foreman for the privately run Wildlife Rehabilitation Center in the Center Glen area, remembers when the colorful yellow-leggeds were plentiful, when their gentle calls of peep-peep-peep could be heard on still nights.

“They were all over the place, especially during breeding season,” he said. “I just hate to see any species leave the mountain.”

Without the yellow-leggeds and other frogs, mosquitoes are gaining in dominance. “The bugs population around here has been going crazy,” Auer said.

It may take a year or longer to get sufficient numbers of frogs in captivity to begin plotting exactly where and when to release them. Because the speed at which frogs mature and reproduce can vary widely because of temperature and other factors, no timetable can be set yet, Lemm said.

Discussions on the best strategy will be held among the zoo specialists and the state and federal agencies.

In the meantime, the lucky seven are being watched day and night. They were brought to the Conservation and Research for Endangered Species facility at the Wild Animal Park last month from Los Angeles.

So far, progress has been encouraging. The frogs’ fungus infections are clearing up, and they are gaining weight.

“He’s a big boy,” Lemm said as he weighed one at 48.1 grams.