I immediately came across one of my target species calling, the Gray Treefrog (Hyla versicolor). I don't have many good recordings of Hyla versicolor so I was glad to find some calling in a "recordable" location. These three frogs were calling from a group of trees probably near a pond off the side of the road.
Later in the evening and just two miles to the SW of this location, I recorded the other species of Gray Treefrog, Cope's Gray Treefrog (Hyla chrysoscelis) calling next to a flooded ditch. It calls four times in this recording as a dry trill/rattle. You will also hear Southern Leopard Frogs (Lithobates sphenocephalus - the chuckling) and Strecker's Chorus Frogs (Pseudacris streckeri - the metallic tinking).
In this second recording you can hear how much drier and more rattling the trill of the Cope's Gray Treefrog is.
But trill rate (pulse frequency) varies with temperature so you have to consider the temperature when identifying Gray Treefrogs by call. In this case, the temperature was roughly the same at both locations (~64°F) and so they are directly comparable. [EDIT - in hindsight and after some more experience with both species, I am not 100% confident in my ability to confirm this as Hyla chrysoscelis. I'm pretty sure, just not 100%. It could just be a weird H. versicolor?]
The Cope's Gray Treefrog (H. chrysoscelis) had a consistent pulse frequency for the few minutes I recorded of 30 pulses per second. All of the many Gray Treefrogs (Hyla versicolor) I heard that night had pulse frequencies ranging between 16 and 18 pulses per second.
Unfortunately, I did find a few Gray Treefrogs on the road which is what is in the photo above. I have a strong feeling that these were Hyla versicolor, but I couldn't say for sure since they weren't actually calling!
© Chris Harrison 2014