People who go hunting don't go by "off the top of their head".

Now I can't speak to the laws in California for hunting, but in Canada they have pretty crazy strict laws regarding illegal hunting, including seizure of anything used in the act (trucks, atvs, guns, boats, etc), removal of gun license, and huge fines.

A quick google search shows the method they've used, and have been using for the last decade as an attempt to stop the spread: Barred owls are much more aggressive, and playing their calls can lure them in to fight, in a way the spotted owls don't, so you don't need to just go based on visual differences. Here's one article about the removal process up to now with an interview of a biologist who's pro-hunting.

Relocation of the barred owls isn't feasible, because no matter where you send them, there's probably already owls there, and relocation often results in the animal dying off anyway.

What's the alternative? Watch as the spotted owls are out-competed and go extinct due to human development and habitat destruction? To me, that seems worse. We already hunt to maintain populations of animals in other species - deer spring to mind. Since we've eliminated many of the deer's predators, we need to maintain that role, which includes setting hunting targets each year. Why are these owls different?