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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Feb 29

Leaping into Foothill Yellow Legged Frog Conservation

Posted on February 29, 2016 at 3:28 PM by Emma Detwiler

written by Elizabeth Ruiz, Watershed Stewards Program Member

The 2016 Frog Docent program at Marin Municipal Water District leapt into action this past weekend! On Saturday, February 27, twelve dedicated volunteers, a mix of new and returning, learned about the foothill yellow-legged frog (Rana boylii), abbreviated FYLF, and how they can connect with their watershed to protect these native, threatened frogs. The weather was clear and sunny; the perfect day for a hike to Little Carson Falls, where the FYLF breed on Mount Tamalpais, and the perfect day to view them sunning on the rocks!
fylf 3
Historically, this species could be found from northern Oregon, west of the Cascades and down the coast to the San Gabriel mountains, in addition to south along the western foothills of the Sierra Nevada Mountains. Today, the FYLF has lost almost half of its range in California alone. Habitat loss, stream alteration, recreation, and introduced non-native predators have all contributed to this reduction and the status of this species is currently under review by the U.S. Fish and Wildlife Service. It is a federal species of concern and a California species of special concern.

Two stable populations of FYLF’s exist within the Mount Tamalpais watershed, on Big Carson, and Little Carson Creeks. Frogs can be found in the pools of the waterfalls at Little Carson Falls, where they breed and attach their sensitive egg masses to the rocks. Egg masses can be trampled or dislodged by people or off-leash pets swimming in the pools. Every egg mass counts! On average scientists from consulting firm Garcia and Associates observe 24 egg masses a year.

Frog Docents provide vital education and protection to the frogs on the weekends, when visitation to the falls is highest. Since the program’s beginning in 2005, docents have recorded 5,600 visitors during the FYFL breeding period which spans March-June, and spoke with 85 percent of them. Of those visitors, 11 percent had dogs, 38 percent of which were illegally off-leash, and almost a quarter of those off-leash dogs were seen in the water.

On a brighter note, they have observed frogs 1,500 times! Clearly this is a popular spot, both for people and for breeding frogs.

If you’re curious about learning more about what you can do to protect the foothill yellow legged frogs, or other Mount Tamalpais native species, contact MMWD’s volunteer program at or call 415-945-1128.

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 Some of the 2016 Frog Docents at Little Carson Falls, after viewing frogs.
 fylf 2
Mating frogs at Little Carson Falls, Photo by Peter Denisevich, 2010


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