'Toads bury themselves in mud and can survive for months until the rains come down," says Diane Nygaard, president of Preserve Calavera, a nonprofit environmental organization that works to protect native habitats around Mount Calavera in Carlsbad. "They retain 30 percent of their body weight in water and store it in their bladders, so they just absorb that as they need to during this long period of waiting for the next year's rainy season." On Sunday, June 24, Preserve Calavera will conduct a hike and training session for people interested in participating in the National Wildlife Federation Frogwatch USA volunteer frog and toad monitoring program. "We're collecting data on the frequency and distribution of frog species across the country," says Nygaard. "I go to a location during breeding season and listen to frog sounds and identify frog species by their sound. There are 7 frog and toad species in our area; 25 in California. I can tell their sex, too -- only the males call, primarily. There are two different kinds of calls. One is the mating call -- the male frogs do it to attract a mate. The other is a release call, because when the frog jumps on the back of another frog, they don't know what sex it is. So if they jump on another male, the male says, 'Ahh, get off of me!'"

Trainees will be led a mile and a half into the Dawson-Los Monos Reserve, beginning in Buena Vista Park and proceeding along the Agua Hedionda Creek, a tributary that flows into the Pacific Ocean. The hike will be followed by a workshop in which volunteers will learn how to identify frogs by sight and sound and how to record the data for the Frogwatch program.

"Toads are just one of the nine families of frogs," Nygaard explains. "So all toads are frogs, but only some frogs are toads. Toads tend to have smaller bodies with short legs and warty skin. Frogs tend to be smooth skinned [with] bulging eyes and long legs." Locals may encounter the Western toad, which is two to five inches long, gray or green with a light stripe down its back, and covered in reddish, black splotchy warts. The National Wildlife Federation warns that toads "secrete a viscous white poison that gets smeared in the mouth of any would-be predator, inflaming the mouth and throat and causing nausea, irregular heartbeat, and, in extreme cases, death." Humans are instructed to wash their hands after handling toads.

One local species, the California red-legged frog, is on the U.S. endangered-species list. The initial decline in numbers of the red-legged frog was in the 1800s, when mining in California muddied and clogged many streams. Later, an estimated 80,000 frogs were harvested for food each year. "A big part of developing recovery plans is understanding what [the frogs'] distribution is," says Nygaard.

Frog and toad calls vary with each species. "Most frogs breathe through their skin, which is called cutaneous gas exchange, but they still have lungs," explains Nygaard. "For most frogs, the lungs are used for vocalization -- they close [their] mouths and noses and push the air out of their lungs into vocal sacs in their throats. The Pacific tree frog is the one you most commonly hear; it goes 'ribbit, ribbit, ribbit.'"

The Frogwatch website offers sound samples and descriptions for most species. The Western toad's call is "like the weak peeping of baby chicks," because this particular toad has no vocal sacs. The American bullfrog sounds a "deep-pitched jug o' rum call that can be heard for more than a quarter mile on quiet mornings." The California tree frog makes "an abrupt low-pitched quack, given during the day as well as at night," and the red-legged frog sounds a "series of weak throaty notes, rather harsh, lasting two to three seconds."

Frogs and toads only call during the breeding season, which varies from species to species. The bullfrog has the longest breeding season, from February to October, whereas the California tree frog's season is only from March to May. The red-legged frog breeds from December to March. "Sometimes you go out and you can distinguish individual frogs," says Nygaard. "Other times there are so many going at once you can't identify anything; right now, I'm just getting a chorus."

Most frogs begin calling after sunset, so volunteers are advised to listen half an hour after the sun goes down. "Frogs are anywhere they can regularly get water; if you walk in your neighborhood, you'll probably hear frogs at night. We aren't tuned in to them, but as soon as you are, it's, like, 'Oh, my goodness! That's a Pacific tree frog, and it's right here,' or 'There's a bullfrog, hiding in those bushes over there!' It surprises me how many I'll hear walking down my street after dark in Oceanside." -- Barbarella

Frogwatch USA Hike and Workshop Sunday, June 24 1 p.m. to 4 p.m. Dawson-Los Monos Reserve Vista Cost: $10 (reservations required) Info: 760-724-3887 or www.preservecalavera.org/activities.html