The Great Horned Owl is a natural predator of peregrines, especially young ones. I remember viewing a video taken by (I think) kayakers on river. It showed a Peregrine approaching fast, coming towards them. There was a Great Horned Owl in a tree near the edge of the river. The Peregrine hit the owl hard, causing it to fall into the river, then continued on its way. At least that's how I remember it.

Does anyone else remember this video?