This Gray Treefrog (Hyla versicolor) was calling from a small roadside tree after some heavy rains in April, 2015 in Bastrop County, Texas.
Eastern Gray Treefrogs are physically indentical to the Cope's Gray Treefrog (Hyla chrysoscelis) but can be told by their calls. This area of Bastrop County, Texas is right at the western boundary of the range of Hyla versicolor in Texas. West of this area, you find Hyla chrysoscelis. There are a few areas where the two species occur sympatrically.
Unfortunately, their ranges are not well mapped out due to the fact that they can't be identified from museum specimens which are traditionally the primary source for creating field guide maps. Many maps simply combine the ranges of the two species implying that they are sympatric over most of their range in Texas which is not the case.
The call of the Eastern Gray Treefrog is a pretty trill with a "bird-like" quality.
When you look at the spectrogram for a single trill, you can see that it is a series of individual notes repeated rapidly in succession.
By counting the individual "notes" and dividing by the time it takes to make those notes, you can calculate that this frog gave 14 notes in approximately 0.6 seconds for a call rate of slightly over 23 notes per second. Cope's Gray Treefrog has a much faster rattle, squeezing in well over 30 notes per second. I have another post comparing the calls coming.
To the ear, the call of the Eastern Gray Treefrog is noticeably different that the dry rattling trill of the Cope's Gray Treefrog. With some experience, you can learn to distinguish easily in the field.
© Chris Harrison 2015