(backyard)

A Little Night Magic

Want to improve the after-hours scene in your neighborhood? Try hanging a screech owl box.

By Kenn Kaufman

 

Night creatures go largely unseen, so people are often surprised to learn that they might have owls as neighbors. But it's true. Take screech owls, for example. Over much of this continent, from southern Canada south into Mexico, they can be common; in fact, studies have shown that screech owls can thrive in small towns, suburbs, even city parks.

Still, in America's tidy neighborhoods, as homeowners and townships trim away dead trees and large limbs and fill in natural cavities, good screech-owl nesting sites can be hard to find. Human-made nest boxes can make up for any shortage of natural nesting cavities, enabling these petite owls to live in places where they might otherwise be absent. This can help stabilize their populations.

There are two widespread species of screech owls, eastern and western, differing most obviously in voice. Neither actually screeches, except when agitated; most of their calls consist of mellow whistles and trills. Screech owls may spend their days sleeping in dense foliage or sitting next to tree trunks (where their mottled pattern provides camouflage), but more often they will be inside a cavity of some sort--a hollow limb, for instance, or a large woodpecker hole--hidden away from the sharp eyes of small songbirds, which will fuss about in a most irritating way when they find an owl sitting on its day roost. While a good cavity can help the owl avoid the annoying attentions of songbirds, it becomes essential during the nesting season.

Screech owl boxes have not inspired as much design experimentation as those for bluebirds or purple martins, but we do have some idea of what works. Fred Gehlbach of Baylor University, the world's leading authority on screech owl behavior, tried some variations on nest boxes as part of his studies on nesting habits. Gehlbach started by measuring natural cavities favored by the owls. He found the birds tended to use deeper cavities, more than 10 inches deep, with entrance holes not much larger than the minimum needed for their own entry. He also found that while the owls would use cavities with floors only six inches across, young owls were apt to fledge too early from such crowded nests. He had better success using boxes with floors that were eight inches square.

Although many experts recommend cleaning out nest boxes yearly, preferably in early spring, there's some disagreement on this point when it comes to screech owls. One reason for this is that the debris you'll find in screech owl boxes may have a life of its own.

Perhaps the oddest part of screech owls' behavior is their association with blind snakes, which have been found in the owls' nests. These odd snakes, which resemble large earthworms, normally appear only at night. Gehlbach and others have observed that the owls bring these small snakes to their nests and release them. The snakes feed on the larval and pupal stages of ants and flies that live in the nest debris, reducing the number of insects competing for the headless mice, dead beetles, and other tidbits cached by the owls. Gehlbach's studies suggest that the snakes actually contribute to the owls' breeding success.

It's important to place the box correctly. The natural cavities that screech owls choose are typically 12 to 20 feet above the ground and in deep shade. As the female incubates the eggs, the male is apt to spend the day roosting in dense foliage within about 20 feet of the nest. After you've placed an inch or so of dried leaves in the bottom of the nest, hang it at least 10 feet up on the trunk of a large tree. Try to place it away from sidewalks or doors, since the owls vigorously defend their nests against perceived threats. In fact, when the young are near fledging, some unusually spunky adults may swoop down at people or pets who wander too close, even raking them with their claws. So while placing the box in as secluded a spot as possible is good for the owls, it might be better for us, too.

Kenn Kaufman is the author of Birds of North America (Houghton Mifflin).

 

 

 


© 2002  NASI

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BUILD IT AND THEY WILL COME:
screech owls

Tools

Ruler or tape measure; pencil; power saw; handsaw; power hand drill with attachments (1⁄2" bit; 5⁄64" bit, to pre-drill the screw holes; 3" hole saw; Phillips-head screwdriver); chisel or knife; hammer.

Materials

  • 1-foot x 10-foot piece of unpainted wood, such as white pine, 1" thick. (Remember that when you buy a board of this size at the average lumberyard or home store, the 1-foot width will really be 11 1/4" and the 1" thickness will really be about 3/4".) You'll end up with leftover wood.
  • 24 Sheetrock screws (2" each), coated or galvanized to prevent rusting
  • One No. 6 brass wood screw (1 1/2"), with washer
  • Two small brass hinges, with screws
  • Several small nails, carpenter's glue, caulking compound

Assembly

(1) Start by remembering this old adage: Measure twice, cut once. Then, with a pencil, mark off all the cuts you'll make, starting from one end of the board, according to the dimensions listed below. After you've made your measurements, cut the piece for the back (32" x 7 3/4"). Next cut the piece for the bottom (8 1/2" x 7 3/4"), then the piece for the front (16 3/4" x 7 3/4").

(2) Cut the sides. First cut a piece that's 10" x 35 1/2". Before you make the next cut, be sure you've measured 17" up one side of the board and 18 1/2" up the other side, and that your cut line connects these two points. You should end up with identical pieces, 18 1/2" in the back, 17" in the front, and 10" from front to back.

(3) Finally, cut the top piece (12" x 11 1/4"--the full width of the board), then a 1" full-width strip (1" x 11 1/4").

(4) Drill two 1/2" ventilation holes about 1" below the top of each side. Drill five 1/2" drainage holes in the bottom (one in the center, one near each corner).

(5) With the hole saw, drill a 3" entrance hole. The center of the hole should be 4" below the top of the front piece. The hole should be centered between the sides.

(6) With the chisel or knife, make horizontal scratches on the inside of the front piece, from the bottom up to the entrance hole (so the young owls can climb out).

(7) Measure about 7" up from the bottom of the back piece to mark where the bottoms of the sides will go. Screw the side pieces into the edges of the back piece; use three screws for each side. The top of the side pieces should slope toward the front. (Pre-drill all the holes with the 5/64" bit.)

(8) Screw the bottom of the box in place, setting it about 1/2" above the bottoms of the side pieces. Use three screws to attach the bottom to each side and to the back.

(9) Screw the front piece in place, aligning it so that its front surface is even with the side pieces. Use three screws to attach the front to each side and to the bottom.

(10) Take the top piece and cut the back end at a slight angle so that it fits flush against the back of the box. (This can be a difficult cut, and might be best made with a small handsaw.) Using the two hinges, attach the top to the back. The top should extend out at least 1" on both sides of the box and overhang the front by about 2". Use the brass screw with washer to attach the top of the box to the front; this will hold the top in place but enable you to open the box to clean out the inside.

(11) Finally, take the 1" x 11 1/4" strip and glue and nail it to the back of the box, above the hinges (use small nails to avoid splitting the strip). The strip should be low enough to help keep rainwater out of the box but high enough that you can still lift the lid and reach inside. Caulk where this piece meets the back.

Hanging the box

The most important thing to remember when hanging the box: Be careful! Ten feet (or higher) is a long way off the ground, especially if you're carrying an owl box. If you don't want to nail or screw the box to the tree, you can attach a cable or light chain to the box through holes drilled in the back (both top and bottom). The cable or chain should be just loose enough to be worked up over the trunk's irregularities. You might need to tighten the cable or chain when the box is where you want it.