Wonderful photos Melanie!
Try this to ID what owl you are hearing. Since you can't see it; you can listen & ID it by the call. I'm going to guess you're more likely to be hearing either a Barred owl or a Great Horned owl.Their calls are very different from one another so it should be easy to figure out. Just click on the little speaker icon to hear their calls.
http://www.allaboutbirds.org/s...