Otus Asio

Eastern Screech-Owls reside permanently south of the Canadian boreal forest, east of the Rocky Mountains to the east coast, and southward in the eastern U. S. to near the Tropic of Cancer in and east of the Sierra Madre Oriental in northeastern Mexico. They are widespread in wooded regions to about 1650 m (5400 ft) elevation and accept urban habitats with wooded aspects and mature cavity trees. There is no evidence of changing abundance generally, but the northern and western edges of range have expanded with increased tree planting, urbanization, and perhaps climatic warming (Gehlbach 1995, 2002a).

TEXAS DISTRIBUTION: Eastern Screech-Owls breed throughout eastern forests and westward in increasingly patchy upland woods and river and creekside forests across the Blackland Prairie, Edwards Plateau, and Rolling Plains to the eastern High Plains. O. a. hasbroucki occupies most of this range, but the smaller O. a. mccallii lives south of the Nueces River and west along the Rio Grande into the Big Bend (Gehlbach 2001a). The small O. a. floridanus intergrades with O. a. hasbroucki east of the Trinity River and mostly south of about 31o N. Latitude (Gehlbach 2002a). Population expansions in the 20th Century apparently increased the overlap of Eastern and Western (O. kennicottii suttoni) screech-owls

ABUNDANCE: In McLennan County, nesting pairs average 1/km2 (2/mi2) in rural habitats to 7/km2 (11/mi2) in suburban Waco, 1967-91 (Gehlbach 1994b). A colonizing population in nest boxes in suburban Temple, Bell County, averages 4 pairs/km2 (6/mi2) in 1994-98 (C. McCollough, pers. comm.). Near the western and southern edges of range, respectively, density is 1 nesting pair/km2 (2/mi2) in Val Verde County, 1973-75, and 2/km2 (3/mi2) in Hidalgo County, 1973-78 (Gehlbach 1987). Populations cycle from high to low numbers about every 4-5 years (Gehlbach 1994b).

SEASONALITY: Eastern Screech-Owls usually lay eggs March 5-May 4 in central Texas; extreme dates are December 15 and June 14 (Oberholser 1974, Pulich 1988, Gehlbach 1994b). Yearling and rural breeders nest about a week later and less productively than older and urban counterparts. Incubation averages 30 days, the nestling period 27 days, and the fledgling-dependency period 8-10 weeks. Egg laying peaks in mid-March, most fledglings appear in May and disperse in late July (Gehlbach 1994b), but nesting averages 2-4 days earlier per decade since the 1960s, coincident with climatic warming (Gehlbach, 2002b).

BREEDING HABITAT: Most wooded sites are suitable if tree cavities or substitutes are available. Habitat area does not matter (Robbins et al 1989). Commonly used forest and woodland associations are longleaf pine, mixed pine-hardwood, deciduous oak-hickory, live oak-juniper, live oak-mesquite, cottonwood-willow, elm-sugarberry, and ebony-tepeguaje. Nests are frequently in oaks, elms, cottonwoods, and pines (Gehlbach 1995). Where Eastern and Western Screech-Owls overlap, Easterns tend to nest nearer permanent water and/or at lower elevations (Gehlbach 1995, Lockwood 2001).

Natural tree cavities formed by wind damage, rotting, and squirrel gnawing are usual nest sites, and large woodpecker holes are used. Substitutes rarely include other kinds of natural cavities such as holes in dirt banks but often include man-made cavities such as nest boxes, porch columns, and mailboxes. Proper nest boxes are accepted as readily as natural tree cavities, especially if the cavities are scarce. The species prefers small entrances and deep cavities (Gehlbach 1994a). Eggs are laid directly on wood or debris at the bottom of the cavity.

STATUS: Eastern and Western Screech-Owls have been considered conspecific (Amer. Ornithol. Union 1983, 1998), so it is difficult to compare historical data with the species-specific breeding bird survey. The two species hybridized in the Big Bend region on the Rio Grande in 1963 (Marshall 1967) and Alamito Creek, 1973 (Gehlbach 1981, 2002a), but Easterns were not recorded west of the Pecos River during the present survey (1987-92). Possibly, the trans-Pecos population was at a cyclic low during this survey and hence undetected (see Western Screech-Owl).

At the western edge of range in a 12-block area from the eastern High Plains east to the eastern Panhandle border and south to the Pecos River mouth and Camp Wood, Real County, all screech owls were less common historically. Oberholser (1974) recorded 11 unspecified sites, whereas the present survey maps 23 for Eastern and 10 for Western Screech-Owls. The three-fold increase in localities reflects both range expansion (Gehlbach, 1995, 2002a) and organized survey efforts by contrast to earlier itinerant record keeping.

Text by Frederick R. Gehlbach (ca. 2002)

Literature cited

Gehlbach, F. R. 2002a. Body size and evolutionary ecology of Eastern and Western Screech-Owls. Southwest. Nat. 47:  In Press

Gehlbach, F. R. 2002b. Messsages from the wild: An lmanac of suburban natural and unnatural history. University of Texas Press, Austin.

Lockwood, M. W. 2001. Birds of the Texas Hill Country. University of Texas Press, Austin, Texas. ress, College Station