The Cope's Gray Treefrog (Hyla chrysoscelis) is a species of tree frog which is found in the United States. It is almost indistinguishable from the Grey Treefrog (Hyla versicolor), and shares much of its geographic range. Both species are variable in color, mottled gray to gray-green, resembling the bark of trees. These are tree frogs of woodland habitats, though they will sometimes travel into more open areas to reach a breeding pond. The only readily noticeable difference between the two species is the call: Cope's has a faster paced, and slightly higher pitched call than H. versicolor. In addition, H. chrysoscelis is reported to be more slightly smaller, more aboreal, and more tolerant of dry conditions than H. versicolor. The range of H. chrysoscelis is more southerly - it is apparently the species found in the lower elevation Piedmont and Coastal Plain of Virginia and the Carolinas. In those areas, H. versicolor may be present only in the Appalachians. The Bird-voiced Treefrog (Hyla avivoca), is similar to Hyla chrysoscelis/versicolor, but is smaller (25-50 mm length, vs. 32-62 mm for the Grey Tree Frogs).
Both Hyla chrysoscelis and Hyla versicolor have bright orange patches on the hind legs, which distinguishes them from other tree frogs, such as Hyla avivoca. The bright yellow pattern is normally hidden, but exposed when the frog leaps. This "flash pattern" likely serves to startle a predator as the frog makes its escape. Both species of Gray Tree Frogs are slightly sexually dimorphic. Males have black or gray throats in the breding season, while the throat of the female is lighter.
The species name chrysoscelis is from Greek 'chrysos' (gold) and 'scelis' (leg).
The two species of Gray Treefrog (Hyla chrysoscelis and H. versicolor) can be told apart by voice, but not by sight. My identification is based on the range map: [link] .
Great composition and detail!