Chimney Sweep

A San Francisco Airport Website Is Crawling With Snakes—And That is a Good Factor

During a typical year there are a few 55 million people pass through San Francisco International (SFO), the country’s seventh largest airport. At some point during their journey to or from the terminal, each of them will travel through a seemingly nondescript 180-acre property, muddy and spartan, bordered by highways and railroad tracks, bisected by rows of power lines. It may look like any other overgrown building lot, but this one is home to the world’s largest population of the strikingly beautiful and critically endangered San Francisco garter snake. A recent study by the US Geological Survey (USGS) confirmed the occurrence of approximately 1,300 snakes on SFO’s West of Bayshore property – the highest concentration ever recorded.

The data marks a hard-won victory for Natalie Reeder, who has worked to keep the site snake friendly for more than a dozen years, first as a consultant and now as an SFO airport biologist. She says airports usually hire scientists like her to keep animals out; their job is to make them stay. Shipowner and her team are responsible for managing the “kind of evil” property west of Bayshore to support the gorgeous but withdrawn snake.

Simply put, the San Francisco garter snake is a stunner. The famous herpetologist and travel guide author Robert Stebbins – a man who had seen many snakes – once considered it “the most beautiful snake in North America”. Though eye-catching and wearing bold stripes in turquoise and red down the length of its four-foot-long body, the snake is notoriously introverted, quick to flee, and difficult to catch. This has made it difficult to count them accurately.

The San Francisco garter snake has been on the federal list of endangered species for more than half a century. Brian Gratwicke, CC BY 2.0 / Flickr

What conservationists have long known, however, is that the snake is in trouble. Endemic only to the San Francisco Peninsula, the showy creature has seen its wetlands filled with fields or paved by urban sprawl. Its main food source, the California red footed frog, has declined for the same reasons. Even if it could find suitable territory, the snake wasn’t safe. The reptile is valued for its exquisite colors and is a popular target for poachers and foragers.

These threats put the San Francisco garter snake on the U.S. Fish and Wildlife Service’s (USFWS) first list of endangered species, published in 1967, though it would take the agency nearly two decades to come up with a recovery plan for the animal. That 1985 document identified West of Bayshore as one of the last remaining places of refuge for the serpent and called for a moratorium on development there. (Just in time too: Shipowner says plans for a subdivision are in the works.) For 23 years, the land remained largely untouched, protected, but neglected, and filled with invasive plants and harmful industrial sewage from the area.

In 2008, according to an unscientific but worrying population survey, SFO took snakes seriously. They worked with the USFWS to develop an updated recovery strategy for the San Francisco garter snake and the most important animal for its survival, the California red-legged frog. This is where Natalie Reeder came in.

SFO Airport Biologist Natalie Reeder has led efforts to protect and preserve the West of Bayshore property.SFO Airport Biologist Natalie Reeder has led efforts to protect and preserve the West of Bayshore property. Courtesy SFO

Since then, her team has worked to rebuild the snake’s goldilocks-like dream home – not too wet, not too dry, open shores for sunbathing, but thick bulrushes to protect against predators. They built rain ponds, deepened existing wetlands, and cleared overgrown drainage canals that benefited both snakes and frogs. Instead of cutting a firebreak every summer and exposing the soft animals to potentially deadly blades and tractor tires, they brought hundreds of goats to clear the land.

Reeder says SFO has also “increased security” and reinforced the property with gates and fences to protect the habitat and prevent illegal collections.

Invasive plants looking for a hold on the site will always be a problem, and thanks to the surrounding impenetrable surfaces, shipowners and their team will likely never be able to isolate west of Bayshore from urban and industrial sewage. But the environmental improvements and increased security seemed to have tipped conditions there in favor of the snake.

The California red-legged frog is the main meal of the San Francisco garter snake.The California red-legged frog is the main meal of the San Francisco garter snake. John Kunna / Courtesy Natalie Reeder

“That is really encouraging [the snakes] can exist in such high urban density, ”says Brian Halstead, a USGS wildlife biologist and one of the study’s authors. He and his colleagues spent two years studying the population and genetic variation of the snakes at the seven known locations. While the team at SFO had good news to report, it found less encouraging data elsewhere.

For one, the populations at four of the sites studied were precariously low, with fewer than an estimated 100 snakes. In addition, all seven locations are geographically isolated and scattered across the peninsula, preventing snakes from moving to and from neighboring locations and potentially compromising genetic diversity. Halsted says improving connectivity will be important to the snakes’ long-term prognosis, including possibly establishing translocation or breeding programs in captivity.

With 1,300 individuals on the 180 acre site, Shipowner thinks west of Bayshore might have “the carrying capacity” for the snake. To prevent overpopulation and improve genetic diversity in other locations, she believes that “some of these snakes need to start moving one way or another”. The USGS study also found that the West of Bayshore property could be an ideal source population to infuse new snakes into other locations.

The San Francisco International Airport site is deep and prone to sea level rise. The San Francisco International Airport site is deep and prone to sea level rise. Russss, CC BY-SA 4.0 / Wikimedia

While shipowner describes the low population figures in other places as “pretty scary”, she is most concerned about the effects of climate change. She says the airport is upgrading its infrastructure to act as a buffer against sea level rise, but the land west of Bayshore is deep and particularly vulnerable to saltwater ingress, which would be fatal to the California red-legged frog. At the other end of the spectrum, the state’s increasingly long and intense droughts could prove disastrous for both species and the humid places they need to survive.

More than snakes and frogs depend on West of Bayshore: Thanks to improvements by Shipowner and her team, the site has attracted a host of other wildlife. The San Francisco garter snake now shares its home with two other species of snake, the gopher snake and the yellow-bellied speeder, as well as deer, foxes, birds and thousands of invertebrates, and shows what is possible, says Reeder, when animals “one have a bit of space and a bit of food. “

Reeder hopes the explosion of life in this overgrown property could inspire people across the peninsula and beyond to help protect urban open spaces, no matter how small or unsightly.

“Nature is not a place to go,” she says. “Nature is here, even in some of the most industrial and commercial areas.”

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