In Search of Tailed Frogs
by Ken Mierzwa
The Marten - Newsletter
The Wildlife Society
Winter 2002 - California North Coast Chapter
Just a few miles from Arcata, California, we bounce down the rutted dirt road, Douglas fir silhouetted against the mid-November night sky. It is clear and cool, with a bright moon. Our four vehicles park along the side of the road.
Lowell and two other Simpson Resource Company ("Green Diamond Timber") biologists, Laura Burkholder and Karen Danner, have put this nocturnal trip together to demonstrate tailed frog inventory methods. The tailed frog, Ascaphus truei, is a primitive creature, and its only two known living relatives are half a world away in New Zealand. All three species inhabit fast flowing mountain streams in forested regions. Male tailed frogs have no voice. Who could hear them above the sound of rushing water? Tadpoles exhibit another curious adaptation, a disk-like mouth part which allows them to hold onto submerged rocks.
We follow Lowell Diller down the steep bank and into the stream. He sets a fast pace for perhaps 200 meters, despite the darkness and numerous slippery rocks and fallen logs. Then we pause and cast our lights over the stream banks. Within moments, Lowell spots the first tailed frog, a juvenile, almost invisible among the fallen leaves.
For many years tailed frogs were considered uncommon. Eventually, biologists learned that nocturnal surveys in the summer months could locate fair numbers of individuals. Usually these were seen sitting in the open on rocks at the edge of the stream. But except in the very best localities, only a handful of frogs were typically observed.
A few months back, Lowell had told us that he had learned of a new eyeshine inventory technique from Gary Fellers of USGS. By holding a flashlight very close to the eyes of the observer, and looking right down the edge of the beam, frogs can be found with relative ease. It turned out that they were not only on the streamside rocks, but that was the only place conventional searches could easily locate them.
So this is our chance to see for ourselves. There are about 16 of us, split into three groups. Our group is farthest upstream. Laura and Karen lead groups to lower and middle reaches closer to the road. The overall group consists of a diverse mix of North Coast Chapter members, including experienced herpetologists, biologists with assorted other specialties, and students from Humboldt State University.
The first frog that Lowell found was sitting in the center of a fallen leaf, on a flat gravel terrace perhaps a meter from the stream. With a little practice, we learn to see the bright but tiny orange eyeshine on this not very large frog, which was a tadpole not so long ago.
Within a minute or two, Don Ashton finds a second frog on the other side of the stream, also on a fallen leaf. Then one of the students sees a juvenile pacific giant salamander (Dicamptodon tenebrosus), also by eyeshine, on the bank a little upstream. A few minutes later, Lowell finds an adult tailed frog. This one is on a withered fern two meters up a steep bank, and the eyeshine is a lot easier to see. Nearby, I notice another tailed frog, this one medium-sized. There really isn't any doubt once I see the eyeshine. The frog is huddled among the stems of low growing herbaceous vegetation. A few more frogs are found before we retrace our steps.
Back at the vehicles, the tally is 19 plastic bags with tailed frogs inside, all males and mostly juveniles. It works out to about one frog per member of the group, for perhaps an hour and a half of effort. Not bad for surveying out of season. Besides the Dicamptodon, other amphibian observations include a red-legged frog (Rana aurora) and a foothill yellow-legged frog (Rana boylii).
Laura and Karen show us how they mark the frogs by injecting colored elastomers into the feet. After a while, the MS-222 begins to wear off. Small groups of people disperse, plastic bags in hand, to release the now colorful but slightly groggy frogs at the flagged capture locations.
Korbel, California - November, 2002