Saturday, February 21, 2009

Night Life at the Ponds

Yesterday we started nighttime pond surveys. Before sunset as we geared up, we could already hear the Pacific treefrogs from ponds over a mile away.

By the time we hiked down in the dark, treefrogs were loudly calling their advertisement songs from every pond & puddle. They would fall suddenly silent when we first approached a pond's edge, but soon one frog would start trilling, and not to be outcompeted, the others would quickly join in.

<--- The local loudmouth, Pacific treefrog in the water. Notice its skinny waist.

Treefrogs spend the nonbreeding season in grasslands and brush usually near locations that hold water for at least part of the year.

<--- A treefrog heading to water.

They have adhesive discs on their toes that allow them to climb objects such as trees, even window glass.
When I find gelatinous egg masses inside of tall, straight-sided cattle troughs, I know the treefrog is the only local amphibian that would be able to suction its way up and into such structures.

Treefrogs are small (up to 2" long not including the legs) and can quickly change their colors. The easiest way to identify them is by the black bar that runs from the tip of the snout through and behind each eye (the masked ranger frog). No matter what color the frog has changed to, the black mask will always be obvious on this small frog.

<--- Male treefrogs inflate vocal sacs to create their impressive chorus and call their mates.

As early-arriving treefrogs finish their reproductive duties, they leave the pond and more partying treefrogs arrive.
Thus, the treefrog breeding song can be heard several months throughout a rainy spring. Pacific treefrog calls have often been recorded as jungle background in Hollywood movies.

Male treefrogs clasp the larger female, called amplexus, and fertilize the eggs as she releases them into the water. The eggs are attached as loose jelly clusters on submerged vegetation.

<--- Treefrogs in amplexus ---

So far, I have only seen a few treefrog egg masses this year. I will post photos once I have some good ones. In the meantime, you can see good photos at California Herps.

Under the din of the treefrogs, we occasionally heard the low chuckling of the California red-legged frog. They start calling later in the evening. California Herps reports that red-legged frog calls last only 1 to 2 weeks at a location. Last year, we heard their calls from mid-February through early April at the Dipper ponds.

<--- Red-legged frog at the Mallard Pond. Photo by K. Greene. ---

We found a red-legged frog sitting in the shallows facing outwards at the Mallard Pond and another one similarly positioned at the Plum Pond.

The red-legged frogs are much larger (5.25" not including legs) than the treefrogs and not nearly as numerous. They have long folds of skin that look like a line running down each side of their backs. Since the red-legged frogs are rare and protected by state and federal laws, we do not pick them up or otherwise disturb them.

<--- Red-legged frog at Plum Pond. ---

California red-legged frogs could be confused with two other large frogs in our area - the native foothill yellow-legged frog or the large introduced American bullfrog. Check the California Herps site for details, however, yellow legged-frogs occur in streams, not ponds and do not have the above-described dorsolateral folds of the red-legged frogs; and bullfrogs can get quite large, usually with a smoother brown-greenish color to their backs, and a tympanum (eardrum that looks like a large flat disc behind the eye) which is larger than the eye. We have never seen or heard bullfrogs at the Dipper Ranch Ponds. This indicates these somewhat isolated ponds are in good shape since bullfrogs eat many of the native amphibians and reptiles.

<--- A red-legged frog egg
mass in the Plum Pond on February 8th of this year. ---

We did not see any egg masses last night, however, cloudy water from recent heavy rains may have been hiding them.

The egg masses float for awhile and then sink, so they are hard to find a few days after being deposited.
I expect the red-legged frogs are just getting started and we will see more of them in the next few weeks.

<--- Last year, I saw much larger red-legged frog egg clusters, the size of cannonballs, in the Plum Pond on February 16th. ---

[03/07/09 revision: I moved the video of the treefrogs to a new posting which includes further discussion of frog calls and a link to recordings of treefrogs and red-legged frogs at the Plum Pond on 02/20/09.]

See Also
  • The CaliforniaHerps site has more information on these frogs including audio recordings of different frog calls.
  • Gayle Pickwell, Amphibians & Reptiles of the Pacific States, Dover Publications, 1972. - although terminology and some information in this book are out of date, Pickwell taught at San Jose State University (known as San Jose State College when Professor Pickwell originally published this book), and provides many detailed observations in the Santa Cruz Mountains.
Pacific treefrog, Pseudacris regilla
California red-legged frog, Rana draytonii
Foothill yellow-legged frog, Rana boylii
American bullfrog, Rana catesbeiana

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