It does look like a nice healthy gray treefrog and only the males call. From my experience, male tree frogs start calling after you enter REM sleep to maximize the amount of sleep deprivation. Years ago I took my sons out frog hunting and we found several tree frogs and we found them by listening for their calls - DUH! The next night I was frantically searching the viv with a flashlight at 3 am to evict them.