I hear these birds far more than I see them, since they forage amid the foliage of brushy areas where their soft green/yellow colors are pretty effective camouflage. They have a distinct high pitched chip sound, and the males have a lovely song. While they forage down low, when it's time to sing, the males will fly up high in a tree to better project their songs.
This shot is a little soft (left the camera at f/10 and a slow shutter speed from shooting some pond scenes - curses!), but I was pretty happy to manage to finally get a photo of one of these birds after seeking them out for a good while.