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In Search of Threatened Frogs on the Red Eye Shift

A night of searching for California red-legged frogs (CRLF)
Ecologists Rich Seymour and Mike Westphal wade upstream beneath a dense swath of poison oak to search for frogs.

Late August twilights have an air of ritual in the hills surrounding Stanford. Light fades away over a quiet campus; raccoons, possums, and other furry quadrupeds perk up; and Richard Seymour wades through poison oak and pools of waist-deep water in search of California red-legged frogs.

California red-legged frogs (CRLF) are a threatened species, and as a species included in Stanford’s Habitat Conservation Plan, the Conservation Program works to monitor and protect them year-round. But the end of summer is a special season. The streams that crisscross the foothills slow to trickles, and deep pools shrink to puddles. Adult frogs congregate near the remaining patches of deep water, while tadpoles rush to sprout legs and lose their tails. It’s the best time of year to count frogs and learn how the population is doing—and that’s exactly what Seymour and the Conservation Program have done each summer since 1996, the same year the species was first listed as threatened. The adult frogs are mostly nocturnal, so nighttime is best for spotting them perched along the stream banks.

Since the mid-90s, Stanford’s population of CRLF has become increasingly restricted to Deer Creek. CRLF are threatened across most of their range, and are locally extinct in some areas. Habitat loss is a key culprit for the species’ decline, and around Stanford, the frogs exist in an environment that Dr. Esther Cole, the Conservation Program Manager, described as “an urban matrix.” There hasn’t been a sighting in San Fransisquito Creek since 2007.

Rich Seymour illuminates a California red-legged frog crouched among tree roots on the bank of Deer Creek.

Carving out a habitat where the frogs can thrive in the midst of Silicon Valley is no simple task. “Recreating some pristine state where the population survives on its own just isn't going to happen here,” said Seymour. “Before the area was urbanized, these streams presumably meandered, sometimes flooded, and left all sorts of oxbows and marshy areas.” Instead of living solely in the creeks, CRLF historically traversed between these marshy pools as well. In fact, Seymour said that in his experience, successful populations rarely survive without access to both separate breeding pools as well as creeks (more details about how Stanford's CRLF breed can be found here.

Replicating these natural pools has been a Conservation Program goal for years, and official permitting to construct them was recently approved. Next summer, the Conservation Program plans to build several artificial ponds for the frogs to breed in near Matadero Creek. If they use them to breed, it could prevent the local extinction of the species, which is otherwise very likely within the next fifty years according to a study the Conservation Program published in the journal Conservation Biology last year. So far, they’re holding on.

“This is such an unusual situation, with this population surviving in a much altered and manipulated environment,” he added.

CRLF occupied areas at Stanford in the 21st century. It’s been over a decade since CRLF have been spotted in San Fransisquito Creek, and Deer Creek (bottom right corner) now supports most of the population.

While searching for frogs in the dark one night, Seymour often observed, rather optimistically, how ‘froggy’ each patch of stream looked. He said that to stay excited for hours of sloshing through poison oak in the dark, it’s crucial to believe you might spy a frog at any moment. If a frog feels cornered, it might make a sudden leap for the deep water. But usually they’re statue-still and identifiable only by the distinctive gleam of a headlamp beam reflecting off their eyes—easy to miss if you aren’t looking carefully.

Just after this comment, another ecologist, Mike Westphal, called him back to a waist-high nook he had passed by, where a fat California red legged frog crouched overlooking the stream.

Seymour laughed and grinned. Even the most experienced frog-spotters sometimes miss one hiding in plain sight.

CRLF have unique spot patterns on their hind legs,
similar to how humans have unique fingerprints. Several
dozen individuals have been recorded over the last two
summers, but it’s too early to draw any major conclusions
about the population.