Thanks all!! I love these little guys. We get them every summer on our back patio, along with the green treefrogs as well. Sparker1, yes, you can tell the difference. Cope’s gray treefrog sounds like a buzzer, while the eastern gray treefrog has a birdlike, musical trill. The only other way to tell them apart is in the lab, and counting chromosomes. Cope's has chomosomes which are tetraploid, thereby having 4 copies of every chromosome, while the eastern gray treefrog has diploid chromosomes, or just two pairs of each chromosome. What can make this even more difficult is that they do hybridize with one another, and so can alter their call, making them even harder to identifiy. That's why I'll just stick with the gray treefrog!! 