The Gray Treefrogs revisited
Hyla versicolor vs. Hyla chrysoscelis

I have several blog entries here discussing the two species of Gray Treefrogs (Hyla versicolor vs. Hyla chrysoscelis).  I won't go into all the details again here, but I just wanted to post a neat recording I got the other night.  

I have been recording Gray Treefrogs in and around Central Texas for several years trying to define the boundaries of their contact.  One thing I hoped to get was a recording of both species calling together.  Fortunately, in May of 2015, I finally got that recording.

In this short excerpt, you hear one Hyla versicolor call followed by a single Hyla chrysoscelis call.  You can hear how much drier and more buzzy the H. chrysoscelis call is than the bird-like nature of the H. versicolor call.

This difference is due to the speed of the trill.  The slower the trill-rate the more "bird-like" it is and the faster the trill the more "buzzy" it is.

If you look at the spectrogram for these two calls you can see the difference in the number of pulses per second.

The first call is the H. versicolor call followed by the H. chrysoscelis call.  This is a direct sample from recording in the field where both species were calling together at the same pond at the same time.  

Looking at the spectrogram, we can measure the number of individual pulses per unit time for each frog.  The first call (Hyla versicolor) consists of 13 pulses and takes 0.41 seconds.  That is a pulse frequency of 31.7 pulses per second.
The second call (Hyla versicolor) consists of 25 pulses in 0.42 seconds for a pulse frequency of 59.5 pulses per second.

Of course, you couldn't count 59.5 pulses per second in the field, but the ear can hear the difference with some training.

Although the pulse rate of both species can vary with temperature, these two frogs were at the same temperature because they were recorded at the same pond at the same time.

© Chris Harrison

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