Owl and Cooper's Hawk behavior

We were out walking at dusk when we saw an interesting encounter between a Great Horned Owl and a Cooper's Hawk. As we approached this large pine tree I kept on hearing this strange squawking. At first I thought it must be a very mad Gila Woodpecker but as we got close to the tree we could see this Cooper's Hawk harassing this huge Great Horned Owl. The owl pretty much ignored the hawk even though the hawk would fly from branch to branch squawking very loudly and on each pass the hawk would try to get close to the owl's head and strike at him. This went on for about 10 minutes until the Cooper's Hawk finally flew away. We searched the tree for a nest but did not see one so I was curious about about this behavior. My guess is that the Cooper's Hawk does not like this Owl (or any Owl's) or it could be a territorial thing? Any other feedback on this would be welcomed.
Regards,
Jim

Hi Jim. I had a similar experience a couple years ago. I heard the Cooper's Hawk, then saw the Great Horned Owl. In my case, crows also joined in and the owl eventually flew off.

I don't know if the owl had a nest there or not, but I don't think it really matters. The bottom line is, raptors simply don't like each other. They view one another as rivals and a threat to their young. It's always the smaller raptor that picks on the larger one, similar to the mobbing action of crows on raptors. In most cases, no harm is done, it just becomes enough of a nuisance that the larger bird leaves the area. When birding, we always pay attention when a bunch of crows are concentrated in one area and cawing continuously. It usually means there is a hawk or owl that they are pestering. Always good to keep your eyes AND ears open.

Yesterday we watched Mew Gulls mobbing a Bald Eagle, when the eagle was at least 200 meters from the Mew Gull's nest. It was pouring rain, and the eagle almost certainly wasn't hunting, but the gulls weren't taking any chances.

I've heard that Great Horned Owls will eat other raptors if they catch them roosting at night including Red-tailed Hawks, so a Great Horned Owl is a thread to the Cooper's and just about any other bird.

This is slightly off topic, but in the last couple of days I've seen Least Terns "mobbing" a Great Blue Heron that seemed to be simply flying over their nesting area and Black Skimmers chasing an Osprey away from their nesting area.