Look What I Found

I took a little trip out to the barn to see what kind of junk I might be able to use for a project I'm working on, and this little dude jumped off of the gate right as I reached to open it.

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He's a cute little guy, isn't he?

I've identified him as either a gray tree frog (Hyla versicolor) or a Cope's gray tree frog (Hyla chrysoscelis). Unfortunately, I can't distinguish any further based on physical characteristics, as the two species look identical.

Physical Characteristics

Both species of gray tree frog are quite variable in coloration and pattern. Generally, they are a mottled grayish to dark-greenish color with some splotch-like patterning. For example, look below to see the images of the specimen that I found.

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Notice that the colors are closer to a grayscale than to green. However, some specimen of gray tree frogs (both species) may not have the mottled patterning. Or, their coloration may be much more toward the green end of the color palette. Like I said: they are highly variable in appearance!

Another physical characteristic to look for is on the underside of the frog. Note the yellow-orange color on the legs.

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And I also thought the little suction cups on the toes were pretty cool.

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These Frogs Are Quite The Chameleons

Another thing that makes these frogs so difficult to identify is the fact that both species can change color from a gray, almost whitish color to gray or green. When I first spotted this specimen, what caught my eye was that it looked white. Unfortunately, I didn't have my camera with me to capture it, and by the time I got it back to the house, it's color had darkened substantially.

Distribution

In Arkansas, most parts of the state are only reported to have one of the two species. H. versicolor is mostly found found in the northeastern part of the state with a couple of small patches found in the extreme southern corners of the state (see the map). H. chrysoscelis occurs everywhere in the state with the exception of the northeastern area where H. versicolor occurs (see the map). So, there are only a few parts of the state where the occurrence of the two species overlaps. There are the two spots in the southern corners, and then there is a little bit of overlap in their range in the northern part of the state. It just so happens that I live in right in that overlap, and that is why I was unable to definitively identify this specimen down to species.

Or Could I?

There are a couple of ways to tell the difference between the two. We could do some DNA analysis. The Cope's gray tree frog (H. chrysoscelis) is diploid, possessing 24 chromosomes. However, H. versicolor has picked up an extra set of DNA somewhere along its evolutionary way. It is a tetraploid with 48 chromosomes.

If only I had a PCR machine in my basement...

But, there is another way! The discerning ear can distinguish between the two species by listening to their vocalizations. The Cope's tree frog's call pulses about twice as fast as that of H. versicolor. To understand what I'm talking about, check out the previous link and scroll about halfway down the page. There is an audio recording of both frogs vocalizing with a labeled spectrograph so you can tell which frog is which.

But even here, you almost have to be hearing both frogs side-by-side. Each species does have a rather wide yet distinct range of pulses that their calls may exhibit. However, the reason that the rate can vary so much within a species has mostly to do with temperature. The colder the temps, the slower the vocalization will pulsate and vice versa. So, if you listen to specimen of H. chrysoscelis during cold weather and compare to H. versicolor in warm weather, there may be some overlap somewhere in the range of 30-something pulses. However, at any given temperature, the call of the former will typically pulse about twice as fast as the latter.

Have you ever found a gray tree frog?

If not, you should get out there and look for one. I'd love to see your pictures down in the comments!

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