I had a meeting at The Raptor Center yesterday. At the end, we got a brief tour, which despite having given hundreds in the past, I was excited to do because it's been about 3 years since I volunteered there and things change quickly. Many of the birds I worked with are still there...as in the turkey vulture who like me is 37 years old. But because it's owl breeding season, the great horned owls were all very hooty in the courtyard. One of the imprinted owls (a bird raised by people and imprinted on them) gives a strange sound for an adult. It barks. This is a sound usually given by immature birds and is associated with food begging. In the wild they would grow out of that. But imprints do it a lot. I think this is a sound people hear quite a bit in the wild at night and since it is such an un owl like sound, it's hard to id.
Here's a video (with a really dramatic title sequence courtesy of Non Birding Bill):