"We put up a nest box for squirrels, and a screech owl moved in. How do we run it off so we can have squirrels?"

To me, that seems like a bizarre request. But that's the question Wes Smith, the University of Georgia Extension Service director in Quitman County, was asked recently.

Most wildlife lovers would rather have the owl. Screech owls are far scarcer and much more interesting to me than the squirrels.

This question is an unusual example of a common problem. If you put up a nest box for backyard wildlife, how do you get your heart's desire to move in?

If you want a bluebird and get a Carolina wren, what can you do? What if you hoped for a chickadee and got a crested flycatcher?

You can apply some wildlife management knowledge to put the odds on your side.

In the case of squirrels versus the screech owl, the squirrels could take the house from the owl if they wanted to. A grey squirrel far outweighs a screech owl. And besides, squirrels sometimes eat nestling birds.

Both creatures will use a nest box with a three-inch-diameter hole.

To favor a screech owl, have the hole in front. To make it easier for a squirrel to enter, put the hole on the side next to the tree trunk.

Mounting a nest box on an isolated tree or a post makes it less appealing to squirrels. They would rather come home by jumping from branch to branch than by running along the ground.

You can increase the chances of getting your favorite bird by putting up lots of bird houses. That's because most cavity-nesting birds are territorial.

Once you have a crested flycatcher in residence, it will prevent other crested flycatchers from moving in nearby. The flycatcher needs to guard a sufficient area to find flying insects for its young.

A bluebird has a different feeding strategy. It gets its insects primarily from the ground, so it doesn't compete with the flycatcher.

A flycatcher will allow a bluebird to occupy a nearby bird box. A chickadee will allow a tufted titmouse to nest nearby but not another chickadee, and so forth.

There are exceptions to the territorial rule. Purple martins and house sparrows, for instance, remain gregarious during the nesting season.

Where you put the next box is important. Some birds prefer a nest box up high in the tree. Others seek a box on a post.

The size of the hole can be important. It's easier to select for small birds than large ones. A large hole admits a wider range of species. A small hole limits the choice to only small birds.

A bluebird needs a hole at least one and one-half inches. A tufted titmouse can enter a one-and-a-quarter-inch hole. A chickadee can thrive in a house with a one-and-an-eighth-inch hole.

Squirrels may enter a house designed for a small bird. They do this by chewing their way in. To prevent this, cut the correct-size hole in a tin can lid and nail it over the hole.

A birdhouse hole doesn't have to be round. A triangular hole will do just fine and is a lot easier to make. Just cut a 60-degree notch at the top of the board in the front of your birdhouse. Put the roof board on, and there's your hole.

Spring is a good time to install nest boxes in your backyard wildlife habitat.

For free birdhouses specifications, send a letter to: Jeff Jackson, Forest Wildlife Specialist, Cooperative Extension Service, 4-404 School of Forest Resources, The University of Georgia, Athens, GA 30602.