Species Profile: Eastern Screech-Owl

by Jack Eitniear

This article first appeared in the February 2006 issue of the San Antonio Audubon Society newsletter.

The Eastern Screech-Owl (Megascops asio) occurs through the eastern threequarters of the state. The owl is often the only resident avian predator of suburban woodlots and often will nest in nestboxes. The owl is unusual in that it comes in two distinctive color morphs: rufous and gray. Many people are not aware that screech-owls are monogamous and polygynous, living in groups of similarly-aged birds within a small territory that contains a number of nestsites. Nesting from March until June, the adults feed their 3-4 young on a wide variety of prey items, which facilitates their being adaptable to a variety of wooded habitats near or within towns.

I should mention that in west Texas we have the Western Screech-Owl (M. kennicottii), which has a descending call, yellowish bill, and in some individuals, more rufous coloration.

Encouraging the breeding of screechowls in your area is often achieved by correctly sized and positioned nest-boxes. According to screech-owl authority, Texan Fred Gehlbach, nest-boxes can be made of any wood at least 2 cm thick. The floor should be 18 x 18 cm with a few (.5 cm) drain holes in the bottom corners. The entrance hole should be 7 cm in diameter and placed 25 cm from the floor. Fred suggests a front sloping lid 5 cm from the entrance hole with 3 cm overhanging and hinged at the back. To save cost I have used wood screws that can be easily removed with a portable drill. Fred suggests that the box be painted dark brown outside which I assume blends the box into the surrounds and protects the wood from the weather. I suspect one could make them from cedar planks that would be more long-lasting and not require painting. Finally, 2 cm of leaf litter or wood shavings should be placed on the bottom of the box.

As an alternative to the classical bird box, one can also use sections of onemeter- long tree limbs. Using a chainsaw, cut the section in half vertically and hollow out the interior. Drill a 7 cm diameter entrance hole as previously described, then wire the limb back together. If you're handy with the chainsaw you can duplicate the cavity of a woodpecker. If not, you may need to nail a lid and/or floor onto the limb. Working with parrots in Mexico, we found that they would not accept the classical bird box but would use a natural type nest. Of course, the natural boxes blend in with the surroundings better than a bird box. I have never read of anyone using this type of box for screechowls but ours in Mexico were widely accepted by all types of birds and small mammals, even killer bees!!!
Screech-owls are dedicated to reproduction and will re-nest up to 4 times in one year if their nests are disturbed. But the objective is to limit disturbances by placing them a couple meters up in a tree allowing for unobstructed flight and lots of shade. Place them no closer than 30 meters from the nest box or known nesting cavity.

While screech-owls have been known to live 14 years, lifespan greatly depends on food resource availability and their skill at crossing highways! Statistically, about 40 percent of young owls survive the first year. While once thought suffering from declines, we now know they experience cycles in abundance with about 4 years from high to low density and 11 years from peak to peak. Rural populations seem to vary more than suburban populations which is interesting as mortality seems to be due to collisions with autos, shooting, cats and dogs, poisoning and trapping. In rural areas, starvation is a problem, so despite the perils, the greater food supplies in suburban woodlots seem to offset the dangers!

For additional information, consider consulting:
--Gehlbach, Fred, 1994. The Eastern Screech-Owl: life history, ecology, and behavior in suburbia and the countryside. Texas A&M Univ. Press, College Station.
--Gehlbach, F. R. 1995. Eastern Screech-Owl (Megascops asio). In The Birds of North America, No. 165 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.