By Diana Dunn
As the sun drops once again into the Pacific Ocean and stars begin to reveal themselves in the clear, autumn sky, moonlight captures purple glowing eyes bobbing along the surface of a pond in our watershed. The eyes belong to a slimy-skinned creature with beefy forearms and semi-webbed feet. No, we do not have a native Swamp Thing roaming our riparian corridors, but California is home to the largest native frog in the American west, the California red-legged frog.
Upon first look, it would seem that the California red-legged frog is an avid belly flopper because of the pinkish to red coloring on the undersides of its thick hind legs. These same legs made the frogs a popular dish in historic San Francisco among both the wealthy elite and countless Forty-Niners. This endemic species had a historical range extending into the Central Valley that reached as far north as Point Reyes National Seashore and continued all the way down to Baja, California. Unfortunately, due to habitat loss, urban sprawl, and pollution, the California red-legged frog population has decreased by 90%; is gone from 70% of its former historical range; and is now considered a threatened species. The only large breeding populations left are located along the coast in San Mateo County to San Luis Obispo County.
Fortunately, there are a number of local organizations, volunteers, and wildlife biologists that are trying to help these native frogs make leaps and bounds in their population numbers. Wildlife biologists are training volunteers or local watershed groups to conduct their own California red-legged frog surveys–which is no easy feat. I learned first hand when I joined SPAWNERS last week in a frog survey training at Wagner Ranch in Orinda. First, surveying groups must trek through creeks or ponds in complete darkness, using only flashlights to try and catch a glimpse of two glowing orbs. But the work doesn’t end there–frog fanciers must then verify the glints they are capturing are from California red-legged frogs and not the eyes of raccoons, spiders, other amphibians or dew jewels. To get a more accurate view, surveyors silently scuttle as close as possible to the frog in hopes that they will be able to spot the identifying characteristics that help differentiate our native frog from the invasive bull frog.
Here are a few tips for catching a glimpse of California red-legged frogs… Our large native frogs have very prominent dorsolateral folds, which look like bulging veins running along each side of their body. They also have distinct banding on the tops of their back legs, and their backs have black spotting with a light center. Their color varies considerably and they can be brown, reddish brown, olive, or grey. They have smaller tympanum, ear drum structures, and eyes than the invasive bull frogs. Following rain events and during the breeding months, November through April, red-legged frogs are much more active. So now is the perfect opportunity to try and sneak a peek of these unique amphibians!
Photo credits: Top two by Gary Nafis, bottom photo by Jason Butler