En Español.

They are secret frogs. Sort of.

Their locations are revealed only on terms of nondisclosure, cross-streets mentioned and then retracted. The frog people are true believers in the virtue of reintroducing frog habitat. They worry about judgmental neighbors.

The few, the proud, the frog people go out after the winter rains, studying the local puddles of the Mission for signs of nascent frog: wriggling tadpole, small nebulas of egg. The frogs mated from February to May, and once the rains start, eggs will be laid.

In one Mission backyard, a woman points sheepishly to a small pool covered by a thick mat of aquatic plants. “I haven’t cleaned this up in awhile,” she says. The egg clusters laid by the frogs attach themselves to standing vegetation in quiet, shallow water; once the eggs hatch, the tadpoles and frogs prefer a cluttered landscape in which it is very difficult for something to see you and eat you.

The woman declines to have her name mentioned. Why all the secrecy?

“Believe me,” says Jim McKissock, an amateur biologist, “there are people who basically don’t care about the frogs. They interfere with the world as they would like it to be. Let’s have more lawns. Let’s have more Frisbee, let’s have more dog areas. That’s the kind of attitude we run into.”

The Mission was once, with its vernal pools, spring-fed seeps and possibly imaginary seasonal Lake of Sorrows, arguably the puddle capitol of San Francisco. But even under the best of circumstances, marshland is not a landscape that has survived the last century well. It is not one that humans are aesthetically fond of. It’s got a reputation for breeding mosquitoes, for being hard to traverse, for being unnecessarily wet and squishy.

It is especially unpopular when it fills up with the effluvia of an entire gold rush town and begins to smell really bad, instead of sort of not great. Early on, the creeks were rerouted underground and the marshes were paved over and filled in.

But in the springtime between May and March, along the banks of old Precita Creek, long buried under Cesar Chavez, in a few places the distinct sound of frog can be heard. The Pacific chorus frog once lived all across San Francisco, and now lives wherever it finds good, neglected weeds and water that never seems to quite dry out.

There aren’t many of these spots left. The old Standard Pacific railyard in Brisbane is, in the absence of any humans who want to use the place, slowly subsiding back into marshland, which the frogs like immensely.

Other spots around the city haven’t lasted long, when they have emerged, says McKissock, who grew up playing in the vacant lots and tidal marshes of the Bay Area. “The last big site was down where Muni headquarters is now,” he says. “They put clay all over where the habitat was. They said it had toxins in the soil.”

The Pacific chorus frog has a croak that has been described as the “classic ribbit,” the one we all remember from cartoons. The background audio for those cartoons was probably recorded by a sound guy in the weeds behind a Los Angeles movie lot — the Pacific chorus frog’s range stretches across the state. When a hole developed in the ozone layer, the frog continued to do surprisingly well; turns out its eggs can handle a lot of UV radiation and still hatch — unlike those of the red-legged frog, which is also local but now listed as endangered, and found nowhere in the city.

The woman who built the pond in the Mission did so more than three years ago, after reading an article that quoted McKissock as looking for people with yards but without dogs (dogs are much more into eating frogs than cats are). He was also looking for, he said, people who wouldn’t get discouraged and give up.

The woman dug a hole in her backyard, lined it, filled it — all to little avail. There were no frogs that year. Or the next year. Or the next.

Then, one night in February, she heard something. Something loud. Mating season had begun, and suddenly her pond was filled with male frogs, all trying to out-ribbit each other. They were very competitive. If her boyfriend walked into the backyard, the low register of his voice would set off a frenzy of croaking. She would wake in the middle of the night to the sound of the frogs trying to prove their superiority as a mate compared to a nearby car alarm.

“I was so afraid the neighbors would get upset,” she says. But the neighbors, so far, have proved tolerant of nature that openly competes with fire alarms — at least until May, when the din stops. “It makes me,” she says, “so happy.”

Probably, says McKissock, the long-term hope for the frogs of the Mission are ponds like these, in private backyards, maintained by people who want to take care of them.

Why does he do this? Pacific chorus frogs aren’t endangered. Scooping frog eggs out of puddles can’t be the most fun way to spend afternoons about town.

“But there were thousands of frogs around the Bay when I was growing up,” he says. Since then he’s seen the wildlife within the city’s boundaries dwindle as its human population has increased. “What if you didn’t see birds anymore?” he asks. “What if you didn’t see butterflies anymore?

“You would miss them.”