Let your eyes adjust to the dim light of the moon and stars. When you do hear an owl, either wait for it to come closer to you, or approach it as quietly as possible. Figuring out where an owl is can be tricky, even when it is loudly informing you of its whereabouts. Western Screech-Owls, Flammulated Owls, and other small species actually have surprisingly soft voices, often sounding farther away than they really are. Estimate your distance from the bird, and then look for it at about half the expected distance.
Some nights owls seem to be everywhere, other nights are all too quiet.
For more information on owls of North America and the world, including pictures and vocalizations that you can download, visit The Owl Pages .