Fowler's Toad (Anaxyrus fowleri) has had a confusing taxonomic history. It started off as a small toad that only occurred in the northeast US. However it was soon realized that it occurred over a wide arear of the eastern US. Its identifty was confused because of its overall similarity to the more western Woodhouse's Toad. It has been regarded as its own species, Anaxyrus fowleri, and as a subspecies of Woodhouse's Toad, Anaxyrus woodhousei fowleri. For our discussion here, I regard them as a separate species, Fowler's Toad.
This is a small toad of the eastern woodland areas from the New England area, across the Mississippi valley and down to eastern Oklahoma and East Texas. It's identity in East Texas has been questioned. See my post about the East Texas Toad here. It does not occur in the far southeastern US. There is an approximate range map from Amphibiaweb.org here.
Here is its range in East Texas (from the North American Amphibian Atlas)
Here is the documented/presumed range of the Fowler's and Woodhouse's Toads in Texas. Their zone of contact/overlap is not well documented. As you can see, historical records have the two species coming together somewhere in East Central Texas, but exactly where this boundary lies is not well resolved. This is complicated by the fact that Woodhouse's Toad populations in most of this part of the state have apparently disappeared and they are very rarely found in these areas anymore.
To further add to the confusion, Fowler's Toad appears to interbreed with Woodhouse's Toad at the western edge of its range, Southern Toads (A. terrestris) at the southeastern edge of its range, and American Toads (A. americanus) at various places in its range.
All the taxonomic issues aside, here is a Fowler's Toad calling in Little Rock, Arkansas.
Pulaski County, Arkansas
Looking at the spectrogram for one trill of this call, it is a typical toad-like trill although it has a "buzzier" insect-like quality to it. The carrier frequency of this call is approximately 1.93 Khz.
So in spite of all the taxonomic confusion, these little "forest toads" of the eastern US persist, even if we don't know exactly what they are all the time.