Frogs are singing for spring in Sonoma County

We humans have come up with some poetic collective nouns for animals. A murder of crows. A parliament of owls. Even a shrewdness of apes (now also the name of a band). So it seems we missed the proverbial lily pad when we came up with the term “army” to describe the millions of frogs that welcome spring with their delightful and often deafening chorus. As few Californians are more joyously vocal about the possible end to the California drought this year, I humbly offer a happiness of frogs as an alternative.

The frogs we hear performing their seasonal symphony right now in the North Bay are Pacific chorus frogs, or sometimes called simply tree frogs. Sticklers for taxonomic accuracy will correctly point out that our local Pacific chorus frog was recently renamed the Sierran chorus frog (Pseudacris sierra) when the genus that was formerly known as Pseudacris regilla was split into three species. Because there remains controversy surrounding the name change, I and many other local naturalists are sticking with Pacific chorus frog as the more descriptive and intuitive moniker.

How do I know it's a Pacific chorus frog?

Pacific chorus frogs range in color through a palette of bright yellow-greens, creamy oranges, reddish tinges, and most commonly a mottled beige or brown. While general coloring of an individual frog does not change, all color varieties have a spectacular ability to adjust their brightness in response to temperature, humidity and even stress. Pacific chorus frogs also vary greatly in size. An adult frog recently transformed from its tadpole form could easily perch on the tip of your pinkie finger. These diminutive “metamorphs” can eventually grow to a maximum of about 2 inches from the tip of their nose to their urostyle, a posterior section of fused vertebrae roughly analogous to a “rump.”

This great variation in both color and size can be confounding for humans. More than a few times, an enthusiastic rainy day hiker has texted me photographs convinced she has discovered at least five different species of frog. Fortunately for budding frog-o-philes, there are two unmistakable features of the Pacific chorus frog, regardless of size or color. All Pacific chorus frogs (indeed all members of the genus Pseudcris) have a characteristic bandit-like dark brown or black stripe across both eyes and all have enlarged toepads, which enable them to climb vertical surfaces.

Our other two native frogs in the North Bay include the medium-sized stream-dwelling foothill yellow-legged frog (Rana boylii) and the larger pond-dwelling California red-legged frog (Rana draytonii). In addition to being larger than the Pacific chorus frogs, neither of these frogs has an eyestripe or bulbous toes. Sadly, both are in serious decline in Northern California because of habitat loss, competition from nonnative bullfrogs and introduced fish and other factors.

Bullfrogs, which are responsible for the decline of many native amphibians worldwide, are easily distinguished from our native frogs by their large size - up to 8 inches long and 1.5 pounds - bulbous eyes, and a green circular external eardrum, called a tympanum, behind the eye.

Although observant hikers may still spot a yellow-legged frog basking on a rock along one of our local streams, few of us are likely to spot a California red-legged frog, as they are confined to a handful of ponds in our area. Despite being named the California State Amphibian by Gov. Jerry Brown in 2014, the California red-legged frog is on the federal list of threatened and endangered species.

Why do frogs sing?

Almost every “why” question in nature boils down to one thing - sex. And like bird song, the frog chorus is an exclusively male club. Each individual male is calling his heart out to lure a female, but en masse the frog chorus is also letting all females know where the good habitat is.

A favorite fake out among frog lovers, which is as instructive as it is fun, is to slowly approach a pond or ditch where frogs are singing and loudly clap. They all stop. A couple minutes later, the “chorus leader” (a large loud frog with prime real estate) starts in with his two-phase call “krick-eek” followed by a second male just a microbeat off sync and then the third. Eventually, all the frogs join in, resulting in the cacophony we call the chorus.

Successful courtship in frogs and other amphibians leads to a kind of mating called amplexus, Latin for “embrace.” Although his precise repertoire of moves vary by species, the general idea is the male climbs on top of and grasps the female with his front legs. She releases eggs in clusters that are bound together in a gelatinous mass, over which he releases his sperm.