Cam-owl-flage. Finding these birds can be extremely difficult unless you have the exact right angle to have a good sighline. They hide in trees with lots of branches. Here the owl is on the opposite side of this dead tree. No real chance of spotting him from here, though you can see him a bit through the middle.
And I am rewarded by spotting Great Horned Owl chick #2 hiding in a nearby Palo Verde tree. Again, if you don't have a good sightline, these birds can be very difficult to find. Here I knew there was likely to be a bird AND I knew it was likely to be in this (and one or two other) trees because they were closest to the nest.