Barn Owls are specialists, eating mostly rodents.

Check the various websites and build a box now ... they will come when they are ready.

You can also encourage rodent-eating hawks by providing them with a tall perch they can use to watch for the rodents. Redtails, especially, like to sit and watch, then swoop.

Barn Owls do eat mostly rodents. However, when I was working in the Chihuahuan Desert of NM, we did find one Barn Owl pellet that contained a sparrow skull. Barn Owls, though, like Lazygardens mentioned, primarily eat rodents. My guess would be that if a Barn Owl does prey on a songbird, it is more of an oppurtunistic event than actually going out and looking for songbirds to feed on.

J

TA:
If you live in Santa Rosa, CA, call some local wineries and ask to speak to the vineyard managers. Vineyards in Sonoma County have put up barn owl boxes for years, with great success (or so I've been told). They might be able to give you some good info.

I wonder whether you ever successfully attracted any Barn Owls?
I will be putting up a box here in the next month.

No, we have not attracted any owls so far. I think it is because it is not high enough off the ground. At the moment it is only about 5 ft off the ground, because my husband was feeling lazy and mounted it on an existing post. I was pretty sure no owls would come to live in it at that height, so I extracted a promise from him that if no owls showed up in a year, we would put up a taller post and put it on that. So I have a few months to wait yet. :)

We also put up a raptor perch at the same time. It is about 20 ft tall, and after several months, we have just recently started to get some hawk action there! In this last week we saw a red shouldered hawk and another hawk we were not able to identify (though I think perhaps it was a juvie red shouldered hawk) sitting on the perch, presumably on the lookout for gophers. :)

Texas_Annie: When I lived in Southern California, half of my time gardening was spent dealing with gophers. People in the East have no idea what these little buggers can do! Once, a neighbor and I were growing giant pumpkins for a contest, and as they grew larger and larger, we would try and lift them off the ground a bit, to guess their weight. Ours were each about 150 pounds, or so, until one day when he lifted his pumpkin, it came right up off the ground. Gophers had tunneled in from beneath it, and eaten all its insides out--nothing but a shell remained. This, after 3 months of special care given the pumpkin. I'm sure he would have liked to wring the little critter's neck.
They do make traps for gophers that are pretty effective. You open their run (when you see soil piled up) and put the trap in the run, then put a board over it. Lifting the board and checking it periodically should yield a squashed little plant-eater. If you continue doing this for the rest of your life, you'll probably keep the gophers under control.

Annie -
Barn owls want a box that is at least 10 feet off the ground, so predators can't jump in and get the babies.

More raptor perches would help - the hawks will not share a perch, but they will share a hunting area if there are several perches.

If pocket gophers are daytime critters Barn owls won't help.
Mary