That's it. I zipped the tent up and fell back to sleep. I have no idea what it was but I've never heard anything like it before or since and I've camped at or near that same spot several times since then.

I did go around the bend later that morning and I didn't find anything with an empty cranium and blood drained, or even any footprints. Maybe it was one of those giant birds that carry off their prey.

Bill