The Presidio is a showcase of successful urban wildlife recovery, where massive efforts to restore marshlands and grasslands have, in turn, invited back former inhabitants, including coyotes, herons, egrets, 25 species of fish, and over 100 invertebrates. It’s a big reason San Francisco is a biodiversity hot spot.
But it could be even richer, says Jonathan Young, wildlife ecologist for the Presidio Trust.
I meet up with Young on a windy, foggy July morning, and he happily points to an empty chrysalis, cream colored with dollops of black and orange, attached to a stone planter wall at the Presidio’s Inspiration Point Overlook.
The chrysalis, where a variable checkerspot butterfly recently emerged, is a sign of a small yet significant victory for what Young calls Restoration 2.0, where species that previously existed in a location are brought back to reestablish a population.
The checkerspot disappeared from the Presidio in the 1970s due to loss of habitat that included the bright orange sticky monkey flower. The flower is now back, and the butterfly, reintroduced by Young and others in 2017, is thriving. “Earlier this year, there were dozens [of chrysalises] along here,” says Young, pointing to the low stone wall.
So far, managed reintroduction is working for the checkerspot. But climate change could imperil another success story, the Sierran chorus frog. It’s tiny, and you’re unlikely to spot one, but thousands of San Franciscans have no doubt heard the classic calls, especially if they live near or stroll past the Presidio’s Mountain Lake Park at certain times of year.
Like numerous species that once crawled, swam, hopped, or fluttered through the Presidio’s warrens, marshes, and hills, the frogs (sometimes called Pacific chorus frogs, but these are in fact a different species), lost most of their habitat to San Francisco’s expansion in the 1900s. The amphibian was able to hold on in a few pockets of the city because it can survive in marshy puddles. It has a prolonged breeding season that starts in November and can go into July, which means they need access to water well into summer.
Trouble is, puddles are having trouble staying wet as climate change brings hotter temperatures and longer droughts. But one small swimming hole gives Young reason for optimism.
A backstage pass
On this midsummer day, Young leads me and Sophia Hosmer-Hughes, an intern from Cal Poly San Luis Obispo, down a hiking path that winds past scrub brush and above grasslands. We pass a couple of people walking dogs and a few hikers, before Young stops and bends slightly to step one leg over the cable fencing.
He stops and tugs at his bright orange vest to show he has the correct credentials. This is the Presidio equivalent of slipping behind the velvet rope.
As we step, the hillside crumbles. It’s not easy to walk down, but its geology is a big reason the pond we’re walking to exists. That’s because the soil contains serpentinite, California’s state rock, and Young notes that serpentine soil is toxic. Only a few rare plants, like Raven’s Manzanita, have adapted and can grow in it. But serpentinite is also porous, which allows water from springs and creeks to seep through, creating an environment that’s unique to this corner of the Presidio.
At the bottom of the hill is a thicket of willows, a sign of a lot of water in the ground. Young points a few feet ahead where the water has pooled in the grasslands. What’s the name of the pond? “Landfill Two. It’s not very exciting,” Young says, “but a lot of these names get made when we’re doing construction and design,” such as restoring creeks and wetlands and enhancing the serpentine grasslands to foster a rich environment for the chorus frogs and other amphibians.
To create that habitat, Young and colleagues dispersed wood from fallen branches and trees to create nooks and crannies where moisture can accumulate and where frogs, salamanders, and the insects they feast upon can hide.
We walk carefully around the pond to look for critters. The pond is teeming with life.
A San Francisco forktail damselfly hovers around the rushes and sedges emerging from the pond. “On a sunny day, there’d be a whole bunch of damselflies going crazy right now. They’re a good indication that the water’s clean, that they have food,” Young adds.
Then he spots a frog, the object of our expedition. Young dips his hands into the water and rubs them together to remove oils that might get on the frog’s skin, which is how it breathes.
He picks up the frog and cups his hands around it. It’s bright green with two thin brown stripes that run from each nostril, over each eye, and end just behind each forelimb. It’s like a little mask. The frog is no bigger than a quarter.
The first 20 years of Presidio restoration relied on ‘build it-and they will come’ to invite back wildlife that could find its way home. But certain smaller critters need help.
The wads of submerged vegetation are a sign the water has a healthy amount of oxygen. That’s good for the tadpoles swimming about — late bloomers. Young says they’ll have time to make the transition to adulthood.
Landfill Two has enough water for now, but it’s not what it could be. “In normal years, when the groundwater table is higher, there would be seeping all over the area here,” Young notes, and shows how he and colleagues have piled cattails around the pond to slow evaporation.
Other Presidio ponds are not so lucky. Another frog habitat, a dune pond fed by seepage near the Presidio Landmark apartment building on the park’s west side, has gone dry.
Guerrilla rescue and restoration
Young once found a colony of damselflies in an unremarkable place, on the side of the road that leads to Fort Point, in “a ditch with random plants in it.” It was, in fact, a mini-marsh, thanks to natural seepage.
Likewise, the chorus frog has been able to hold on in the oddest places in San Francisco. In an industrial drainage ditch near Islais Creek, a small colony has lived since the early 2000s after a forced relocation to escape construction of a new bridge. Local herpetologists have kept an eye on the population, one of the oldest genetic lines of chorus frogs in the city.
Young says neighbors rescued another colony from a toxic spill in a Muni maintenance yard in Potrero Hill and placed them in a nearby community garden.
Frog friends have also built backyard habitats, including submerged bathtubs, to help boost the population. But these efforts have met with some resistance. When certain homes changed hands, the new residents were not too keen on scientists monitoring their backyards. In other instances, neighbors complained of the frogs’ loud presence during breeding season. (They don’t call ’em chorus frogs for nothing.)
Backyard builders creating small unconnected patches of territory can only do so much, Young cautions. To truly reestablish the chorus frog in San Francisco requires more sustainable efforts.
The same caution applies to his work.
The first 20 years of restoration in the Presidio relied on the “build it and they will come” mode of revival. Reestablishing native plants and daylighting creeks created environments that invited back a lot of wildlife. Those that could return by walking (coyotes) and flying (Western bluebirds) found their way. But certain smaller critters need help, according to Young.
“In an isolated area like the Presidio, smaller things like frogs and damselflies can’t make it here from other locations because it’s surrounded by ocean and the city and all that stuff,” he says. (Other 2.0 projects include the ringlet butterfly, the California floater mussel, and the Olympia oyster.)
Since 2014, when Mountain Lake was cleaned up and restored as a habitat for native species like the chorus frog, Young and others have been transferring the frog’s gelatinous clutches of eggs from the lake to dune ponds and wetlands elsewhere in the Presidio.
But these eggs are all from the same population, and Young is worried about a genetic bottleneck, which happens when a small population of a species is started from a few members of an original population. It reduces the genetic diversity, which lessens the chance a species can adapt to changes.
In the case of the Presidio frogs, having the ability to morph faster from tadpole to adult frog would be useful when their aquatic environment is drying out more quickly. Where to get that diverse gene pool is a question local researchers will investigate as part of this new, 2.0 twist on ecological restoration.
Young relishes the challenge. “We’ve turned the tides for the better so far,” he says. “It’s a really exciting time because not many people around the world have really thought about reintroducing wildlife into urban areas.”
Kristi Coale (@unazurda) is a San Francisco-based freelance writer and radio producer for various outlets, including KALW’s Crosscurrents and the National Radio Project’s Making Contact.