The Frogs of Mountain Lake

She got me up all night, all I’m singing is love songs

In the chilly, damp, Northern California winter, the young males gather at the water’s edge after dark. They sing, not quite in harmony, but loudly. Night after night, they get together and sing. And soon, the young females hear the love songs, and come to see who these performers are.

But this isn’t Outside Lands, or any of the dozens of outdoor concerts held in San Francisco. This is the beginning of mating season for the Pacific Chorus Frog, Pseudacris sierra.

These frogs are small, less than two inches long — about the size of a prune. They spend their days hidden under leaves or logs. Their varied color, from emerald green to charcoal grey, helps them blend into the background.

Listen to Pacific Chorus Frogs and watch while the author draws one of the singers.

But the sound these frogs make is huge. When hundreds of males gather together and sing, the chorus drowns out any other nighttime sounds. The genus name, Pseudacris, means “false cicada,” and for anyone who’s heard cicadas on the East Coast or the Midwest, it’s an apt comparison.

And thanks to Hollywood, the world knows the sound of these frogs. When filmmakers needed to record swampy sound effects, they turned to the nearest talent. So these Chorus frogs produce the familiar “ribbit” heard in movie after movie.

Like three-spined sticklebacks and freshwater mussels, Pacific Chorus frogs are one of the native species that biologists are reintroducing at Mountain Lake, in San Francisco’s Presidio. The tadpoles eat algae, and the adults feast on insects. In turn, the frogs are food for garter snakes, herons and raccoons(1).

For years populations of amphibians around the world have been collapsing. Many factors, like habitat loss, contribute to the problem. And one kind of fungus, chytrid, spread by the food and pet trade, has decimated frog populations. For reasons that aren’t entirely clear, Pacific Chorus frogs exposed to chytrid don’t succumb to the infection. However, being impervious to the killer fungus isn’t all good news. Like little Typhoid Marys, the Pacific Chorus frogs are carriers, spreading the fungus and potentially threatening other local amphibians.

A sample of the color variety of Chorus frogs. Art by author

Fortunately, frogs’ eggs do not carry the chytrid fungus, so Presidio biologists could relocate Pacific Chorus frog egg masses safely, without spreading chytrid. In the winter of 2015, Pacific Chorus frog egg masses were placed in submerged cages, protecting the eggs and tadpoles from predators. And the population has thrived since then.

For the next few months, the Chorus frogs will be gathering and singing, in bigger and louder groups. Go to Mountain Lake(2) after dark and enjoy one of the best free concerts in San Francisco. All they’re singing is love songs.

1. Monty Python fans may insert their own joke here.
2. If you don’t happen to live in San Francisco, chorus frogs are common from Vancouver to San Diego. Contact your local naturalist!
3. If you DO live in San Francisco, check out the many volunteer opportunities in the Presidio.

Title image Creative Commons, courtesy The High Fin Sperm Whale