Greeting from a Great Horned Owl

After a couple evening walks, we've returned to the house to hear a cacophony of birds. The Western Kingbirds are flying around squawking, American Kestrels are diving in the treetops, European Starlings are flapping away. Why so much noise? Because a Great Horned Owl likes to hang out in our yard. So whenever I hear the birds, I start looking around until I spot the owl. The owl knows us fairly well, so it lets me get close to get a photo. We've actually had a family of Great Horned Owls around, but they seem to have dispersed and now I only see one owl at a time.
We sleep with the windows open and quite often at night we can hear the owl hooting away. I'm always thankful that the owl is helping to keep our yard free of gophers and mice. Our puppy Henry was quite scared of the owls when he was smaller, but now he's gotten so big that he just ignores them.  I try to hoot to the owls to encourage a conversation, but they just ignore me. I wonder why.