03/31/2017 The Ballad of the Lonely Frog

03/31/2017 – The Ballad of the Lonely Frog (Karen Benson)

This tiny fellow is a Rio Grande Chirping Frog. He is less than an inch long! These frogs are terrestrial and are not found in ponds. Instead they live under rocks, paving stones or deep in the leaf litter. They come out to feed on tiny insects and spiders at night. In the past few decades, these Chirping Frogs have been hitchhiking rides in potted plants from the Rio Grande Valley to all parts of Texas. This photo was taken in the Big Thicket National Preserve in east Texas. Wikimedia Commons Photo.

“Chirp.”   This sound was followed by five seconds of silence.  “Chir-rup.”  Another silence.  Then “chir-rup” again.  The chirping resembled a cricket calling, but different in tone and in the irregular spacing of the chirps.  It was emanating from under the deck…or possibly from the heavily mulched flowerbed.

I could see nothing that could be making the sound.   It was evening and the waning light didn’t improve my chances to find the creature.  Instead, I concentrated on the sound, memorizing it.

Using a Guide to Night-Singing Insects of the Northeast (Himmelman, 2009) and its accompanying audio CD, I decided that an insect was NOT the source of the chirping.

My next guess was some sort of frog.  The Internet has a number of websites that play frog calls.  I worked my way through Leopard Frogs, Bullfrogs, Chorus Frogs, Cricket Frogs, and finally played the audio clips of Chirping Frogs.  Bingo!

I had some sort of Chirping Frog.  Three species (Spotted, Rio Grande, and Cliff) Chirping Frogs are found in Texas.  The sound of the Rio Grande Chirping Frog was the best fit.   The Field Guide to Reptiles and Amphibians of Texas (Garrett and Barker, 1987) describes the Rio Grande Chirping Frog’s voice as “an abrupt cricket-like chirp consisting of one or two notes repeated at irregular intervals.  Calls are not loud, but they can be heard most of the year whenever it rains.”

Well, it certainly was calling but when I tried to find the creature, it seemed to have a ventriloquist’s technique.  I had also read that they are extremely small:  only 5/8ths to one inch maximum in length.   It is challenging to find something so small, especially since they are brownish-gray and blend in with the leaf litter.  I looked and looked but I did not find one that night.

The field guide also pointed out that these Chirping Frogs are native to the extreme southern tip of Texas in the Rio Grande Valley.  How could I have one under my deck in Bee County?  The Internet turned up an interesting fact.  The Rio Grande Chirping Frog was introduced to other parts of Texas by way of the potted plant nursery trade.  The first confirmed sighting in Houston was in 1984.  Since potted plants grown in the valley are sold throughout the state, it is no wonder that these little frogs are hitchhiking to new destinations.  They have been reported from all over the southern half of Texas.

You would think that a delicate semi-tropical frog would not survive out of the Valley.  But they have, and in many cases, seem to have established new populations.  A study published in 1992 suggests that they can persist far north of their native range by taking refuge under paving stones and ornamental rockwork.  The stones retain heat and moisture for the frogs.  A well-watered potted plant on a patio would mimic these frogs’ natural environment of moist palm groves, thickets of vegetation along irrigation ditches, and debris piles.

You are not likely to find a Rio Grande Chirping Frog in a pond, however.  Chirping Frogs belong to a genus of tropical frogs that are, in fact, terrestrial.  Unlike most amphibians that must lay their eggs in water, Chirping Frogs lay their eggs in moist soil.  And it gets weirder still.  These frogs are “direct developing frogs” meaning that the eggs hatch directly into a frog, not a tadpole.  They have developed the ability to skip a stage in their lifecycle that is vital to other amphibians.

Don Wells, a professor of biology and biochemistry at the University of Houston  has said : “Amphibians are supposed to lay their eggs in water, hatch, swim around and metamorphose to become terrestrial—to a large extent, that defines an amphibian.  This frog doesn’t like water at all.  It buries its eggs in the ground and, in about three weeks, they hatch out as tiny froglets.”

Dr. Wells has proposed the idea that this unusual lifecycle is due to a “genetic master switch.”  He believes that the master switch is a single gene that is capable of turning on or off metamorphosis.  I wonder how this might work.  If the gene is off, then the amphibian should stay in the tadpole stage.  If it is on, then the tadpole should metamorphosis into a frog.  Perhaps it is in the timing of the switching the gene on.  If that occurs while the embryo is still in the egg, then when the egg hatches, a froglet emerges.  Interesting…

So if you hear those plaintive chirping calls in your backyard, you may have a lonely Rio Grande Chirping Frog, hoping for a mate.  Maybe he will find one in that new tropical plant you just bought for your garden or patio.  And maybe, just maybe, you will see some really tiny froglets this summer.  Let me know if you do!

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