From ferns to frogs

The ferns are not the only thing calling the hoop houses at my Richmond, CA field site home. In mid-May I started noticing small frogs, most likely ​​Pacific Chorus Frogs (Pseudacris regilla) among the ferns, perching on pinnae or resting in frog-sized cavities of the greenhouse. I was fascinated, but also concerned. Animal interactions are a classic concern in phytoextraction research. The ferns that the frogs call home are full of arsenic. If the frogs were somehow ingesting the plant tissue, it could prove toxic to the frogs and transmit arsenic up the food chain to racoons and other frog predators. Frogs aren't known to eat plant tissue, however. Perhaps they are feeding on the mosquitos and mosquito hawks that also seem partial to the humid greenhouse oasis in the otherwise dry and windy San Francisco Bay shore summer air. Or perhaps the greenhouse offers shelter from birds of prey.

---

A frog resting in a cavity of the hoop house, just above my work table. It stayed there all afternoon, unperturbed by my sampling activities. Pacific Chorus Frogs exhibit an impressive array of colors and patterns along the green-brown spectrum, including an almost iridescent bronze (below).

I came back from installing vacuum syringes to withdraw porewater samples to find this frog sitting on my 50-ml tubes.

It sat there for quite a while, tolerating my diversions into artistic photography.

Finally it relocated to the shelter of the syringe box, pausing on the side of the tubes for a moment. The toe pads, along with the eye stripe, indicate it's a Pacific Chorus Frog.

On June 14, about a month after I first observed the frogs, I noticed small frogs -- and lots of them! These young frogs are about a centimeter wide. The time from egg to tadpole to metamorphisis can be several months. The adults probably migrated to the greenhouse from their breeding grounds, possibly vernal pools in the restored coastal terrace prairie, with the young frogs following post-metamorphosis. Adult frogs have been observed up to 300 meters from their breeding pools, where they will return the following year.

The number of young frogs in the greenhouse was impressive. Fifteen to twenty? They seemed to be everywhere I looked, including lined up on this plot divider stake!