Canyon Treefrog
Hyla arenicolor

The Canyon Treefrog (Hyla arenicolor) is a unusual treefrog of the southwestern US and central Mexico.  This frog ranges in rocky mountain canyons of southern Colorado and Utah south through Arizona, New Mexico and western Texas down through the plateau of central Mexico.  Although it has a wide range it is generally only found in wetter canyons of this area, particularly along the few permanent streams that dissect these mountains.  Large parts of its range on the map are too dry and inhospitable to hold populations of these frogs.  Even in areas where they are common, they may be difficult to find during the drier times of the year.  Only during the rainy do they come out in large numbers to breed in the streams and pools that form in their canyons.

They are generally grayish or brownish with darker brown/gray spots on their back.  There is usually a little yellowish wash around the hind limbs.

Although it shares the common name "treefrog" with the other members of the genus Hyla, this frog is much more likely to be found clinging to the side of a boulder than in or near a tree in its desert canyon home.  They are amazingly tolerant of heat and drying out.  It is not unusual to find them sitting on the side of a boulder or canyon in the heat of a desert day just waiting for the cool of the evening or an afternoon shower to become active.

Canyon Treefrogs have an unusual double vocal sac that is different than that found on many eastern members of the genus Hyla.  This, as well as their dry rattled call reminds me of the neotropical frog genus Smilisca more than the eastern Hyla.  Current phylogenies place them with the other western treefrogs in the genus Hyla or even near the eastern treefrogs.  They are not closely related to the tropical Smilisca treefrogs.

You can see the ripples created in the water around this calling Canyon Treefrog.

The call of the Canyon Treefrog is a very loud, dry rattle.  The rattle is lower pitched than the rattling calls of species like the Cope's Gray Treefrog.

A spectrogram of a single rattle is shown below.  Each individual call lasts around 0.8 seconds with a pulse rate of about 27 pulses per second.  This pulse frequency is probably temperature related as it is in other Hyla.

There is a regular pause between the calls which average around 1.3 seconds for this individual (which was fairly typical for the place/time/temperature at which I was recording).

A chorus of these frogs can make quite a racket.  In this recording of a small group, you can hear how the frogs not only attempt to alternate calls with each other in time, they also choose different carrier frequencies (dominant pitches).  This is believed to help females hear the difference between the calls of each individual.

Here is the spectrogram of a pair of those calls.  The louder of the two frogs (it was closer to the recorder on the left) has its carrier frequency at around 480 Khz while the other (right) frog responds with a slightly higher call at 539 Khz.  This is easy to hear in the recording as well as see on the spectrogram.

Here is another recording is of the same canyon full of Canyon Treefrogs but recorded further away from the chorusing frogs.  You can hear how the individual calls seem to blend into a constant roar as they bounce around the walls of this narrow canyon.

Hyla arenicolor chorus in canyon - Davis Mountains, TX

When calling, males perch from canyon walls, rocks and boulders in the stream as well as shallow areas of the stream itself.  Here is a short video of one calling.  You can see the ripples form in the water around the frog from the vibrations of his body.

© Chris Harrison 2015

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