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WILDLIFE SPECIES:  Megascops asio


WILDLIFE SPECIES: Megascops asio
AUTHORSHIP AND CITATION : Sullivan, Janet. 1995. Megascops asio. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].

ABBREVIATION : MEAS SYNONYMS : Otus asio (Linnaeus)[27] COMMON NAMES : eastern screech-owl common screech-owl shivering owl little horned owl little dukelet demon owl dusk owl TAXONOMY : The currently accepted scientific name of eastern screech-owl is Megascops asio [41]. It is a member of the family Strigidae [27,41]. It was recently split from western screech-owl (M. kennicottii) which was formerly treated as a subspecies [3,21]. These two species interbreed in the Big Bend region of Texas, where their ranges overlap [21]. Marshall [21] accepted five subspecies: M. a. maxwelliae (Ridgway), Rocky Mountain screech-owl M. a. hasbroucki (Ridgway), Hasbrouck's screech-owl M. a. mccalli (Cassin), Texas screech-owl M. a. asio (Linneaus), southern screech-owl M. a. floridanus (Ridgway), Florida screech-owl ORDER : Strigiformes CLASS : Bird FEDERAL LEGAL STATUS : See OTHER STATUS OTHER STATUS : The eastern screech-owl is listed as a species of special concern on the American Ornithologists' Union Blue List. It was first blue-listed in 1981, and was listed again in 1982 and 1986. Numbers of eastern screech-owls have been reported as declining on the Hudson-Delaware, southern Atlantic Coast, and in Appalachian and mid-western prairie regions [34].


WILDLIFE SPECIES: Megascops asio
GENERAL DISTRIBUTION : The eastern screech-owl is found in eastern North America and northeastern Mexico. Its range extends across southern Saskatchewan, southern Manitoba, northern Minnesota, northern Michigan, southern Ontario, southwestern Quebec, and Maine; south through eastern Montana, eastern Colorado, and Texas to central Nuevo Leon, eastern San Luis Potosi, and southern Tamaulipas; east to the Gulf Coast and southern Florida [1,27]. At the western edges of its range, it appears to be confined by the eastern front ranges of the Rocky Mountains in Wyoming, Montana, and Colorado [1,13,22]. Distribution of subspecies is as follows: Rocky Mountain screech-owl: Southeastern Saskatchewan, southern Manitoba, eastern Montana, and the Dakotas south to eastern Wyoming, western Nebraska, western Kansas, and northeastern Colorado. Possibly also breeds in central Alberta, but these birds may be western screech-owl. Hasbrouck's screech-owl: Central Kansas to Oklahoma and Texas. Texas screech-owl: Lower Rio Grande to the southern border to Tamaulipas. Southern screech-owl: Minnesota, peninsular Michigan, southern Quebec, and southern Maine south to Missouri and northern parts of Mississippi, Alabama, and Georgia. Florida screech-owl: Florida and the Gulf Coast west at least to Louisiana and north to Arkansas [18]. ECOSYSTEMS : FRES10 White-red-jack pine FRES11 Spruce-fir FRES12 Longleaf-slash pine FRES13 Loblolly-shortleaf pine FRES14 Oak-pine FRES15 Oak-hickory FRES16 Oak-gum-cypress FRES17 Elm-ash-cottonwood FRES18 Maple-beech-birch FRES19 Aspen-birch STATES :


BLM PHYSIOGRAPHIC REGIONS : 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K081 Oak savanna K082 Mosaic of K074 and K100 K084 Cross Timbers K089 Black Belt K093 Great Lakes spruce-fir forest K094 Conifer bog K095 Great Lakes pine forest K096 Northeastern spruce-fir forest K097 Southeastern spruce-fir forest K098 Northern floodplain forest K099 Maple-basswood forest K100 Oak-hickory forest K101 Elm-ash forest K102 Beech-maple forest K103 Mixed mesophytic forest K104 Appalachian oak forest K106 Northern hardwoods K107 Northern hardwoods-fir forest K108 Northern hardwoods-spruce forest K110 Northeastern oak-pine forest K111 Oak-hickory-pine forest K112 Southern mixed forest K113 Southern floodplain forest K114 Pocosin K115 Sand pine scrub SAF COVER TYPES : 1 Jack pine 5 Balsam fir 12 Black spruce 14 Northern pin oak 15 Red pine 20 White pine-northern red oak-red maple 21 Eastern white pine 22 White pine-hemlock 23 Eastern hemlock 24 Hemlock-yellow birch 25 Sugar maple-beech-yellow birch 26 Sugar maple-basswood 27 Sugar maple 28 Black cherry-maple 39 Black ash-American elm-red maple 40 Post oak-blackjack oak 42 Bur oak 43 Bear oak 44 Chestnut oak 45 Pitch pine 46 Eastern redcedar 50 Black locust 51 White pine-chestnut oak 52 White oak-black oak-northern red oak 53 White oak 55 Northern red oak 57 Yellow-poplar 58 Yellow-poplar-eastern hemlock 59 Yellow-poplar-white oak-northern red oak 60 Beech-sugar maple 61 River birch-sycamore 63 Cottonwood 64 Sassafras-persimmon 65 Pin oak-sweetgum 72 Southern scrub oak 87 Sweetgum-yellow-poplar 88 Willow oak-water oak-diamondleaf oak 89 Live oak 93 Sugarberry-American elm-green ash 94 Sycamore-sweetgum-American elm 95 Black willow 96 Overcup oak-water hickory 108 Red maple 109 Hawthorn 110 Black oak SRM (RANGELAND) COVER TYPES : 810 Longleaf pine-turkey oak hills 811 South Florida flatwoods 812 North Florida flatwoods 813 Cutthroat seeps 820 Everglades flatwoods PLANT COMMUNITIES : The eastern screech-owl occupies a wide variety of habitat types [29]. It is commonly associated with open woodlands of oaks (Quercus spp.), maples (Acer spp.), and hickories (Carya spp.); it is also found in pine (Pinus spp.) forests and plantations, mixed woodlands, orchards, and forested wetlands [28]. At the northern and western edges of its range, the eastern screech-owl occupies riparian woods dominated by hardwoods including boxelder (Acer negundo), green ash (Fraxinus pennsylvanica), and bur oak (Quercus macrocarpa) [23]. In South Dakota eastern screech-owls were found in riparian woods dominated by eastern cottonwood (Populus deltoides) and willows (Salix spp.), hardwoods dominated by green ash, boxelder, American elm, and bur oak, and shelterbelts. Siberian elm (Ulmus pumila) is a common shelterbelt tree in South Dakota and is used by eastern screech-owls [12]. In Kansas eastern screech-owls were also observed in shelterbelts [26]. In New England, eastern screech-owls are found in aspen (Populus spp.), paper birch (Betula papyrifera), northern hardwoods, red maple (Acer rubrum), balsam fir (Abies balsamea), eastern hemlock (Tsuga canadensis), northern red oak (Quercus rubra), eastern white pine (Pinus strobus)-northern red oak-red maple, and eastern white pine communities [11]. In South Carolina on the Coastal Plain, eastern screech-owls were observed in pine and hardwood stands. The managed pine stands were mostly longleaf pine (P. palustris) and loblolly pine (P. taeda). Hardwood stands were dominated by gums (Nyssa spp.), baldcypress (Taxodium distichum), oaks, or red maple [17]. In Louisiana eastern screech-owls were found in mature mixed bottomland hardwoods dominated by water oak (Q. nigra), pignut hickory (Carya glabra), American elm (Ulmus americana), and sugarberry (Celtis laevigata). They also inhabited cottonwood plantations and riverfront hardwoods dominated by sweet pecan (Carya illinoiensis), water hickory (C. aquatica), sugarberry, and waterlocust (Gleditsia aquatica) [24]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Megascops asio
TIMING OF MAJOR LIFE HISTORY EVENTS : Diurnal Activity: Eastern screech-owls are rarely active before dusk. In Ithaca, New York, the earliest recorded time of initiation of feeding activity was 8:25 p.m.; the latest time feeding ended was 4:15 a.m. [39]. Migration Status: Eastern screech-owls are resident throughout their range; suggestions that some migration occurs at the northern edge of the range have not been substantiated [18]. The large majority of adult birds (87%) were recovered within 10 miles (16 km) of the banding site. None had moved more than 40 miles (64 km) [37]. Pair Bond: Craighead and Craighead [7] stated that they had no data on year-round pairing, but they observed birds that appeared to remain loosely paired over the winter, using the same hunting areas and roosting sites as during the breeding season. They delimited the beginning of the breeding season by the selection of a nesting territory; in Michigan this usually occurs around the end of February [7]. Nesting: Peak nesting season, when young are in the nest, appears to coincide with most passerine migration (a rich source of prey) [37]. In the Southeast, nesting season is from mid-March to late May, peaking in April [15]. In Michigan earliest egg date was April 18 (1942) [7]. In New York and New England, egg dates ranged from April 12 to May 18. In Pennsylvania and New Jersey eggs were present in nests from March 23 to May 19, and in Florida, eggs were present from March 11 to May 18 [18]. The shortest time between eggs is 48 hours; the time between eggs is often 72 hours and occasionally longer [19]. Typical clutch sizes are 3 to 5 eggs; clutch sizes range from 1 to 10 [18]. Incubation: Incubation is almost exclusively by the female; if she leaves the nest to drink or bathe, the male will incubate until she returns and pushes him away. The male brings food but the female eats very little during incubation [19]. The incubation period is variable, lasting from 26 to 32 days [37]. Development of Young: The altricial young are downy, with eyes closed [19]. The young have been observed shivering almost constantly for the first 2 weeks of life [5]. The eyes are usually open by the 20th day. Flight feathers begin coming in around the 25th day. The average time in the nest is 4 to 5 weeks [7,19]. Fledglings stay on branches near the nest until full flight is achieved. Even after leaving the nest tree, fledglings continue to be fed by the parents for up to 5 weeks after fledging. By the ninth week, fledglings usually begin molting to the first-winter plumage. In Ohio the overall nesting success rate (the proportion of active nests that fledged at least one young) was 86.1 percent, and the overall breeding success rate (the proportion of eggs that resulted in young fledged) was 73.8 percent [37]. Juvenile Dispersal: Family groups begin to split up by late August. Dispersal, in an apparently random direction, occurs in early fall [18,19]. In a Connecticut banding study, juvenile dispersal fell into two groups; juveniles either travelled fewer than 20 miles (32 km) or much greater distances (a minority). The longest distance recorded for juvenile dispersal was 185 miles (300 km) [37]. Breeding Age and Longevity: One banding study indicated that at least 25 percent of eastern screech-owls bred as yearlings [37]. In the wild, the average lifespan for eastern screech-owl in central Texas was estimated as 3.6 years, although some individuals survived to at least 8 years of age [14]. Captive birds have lived more than 20 years [19]. PREFERRED HABITAT : Suitable eastern screech-owl habitat seems to be wherever nesting and roosting cavities are near or adjacent to open areas with available rodent prey [29]. Eastern screech-owls usually inhabit open woodlands adjacent to meadows, marshes, or fields; forest clearings; old orchards; and parks and other open areas in urban or suburban areas [10,9]. They are more tolerant of human habitation and human activities than other owls, and are found in or near barns, outbuildings, birdhouses, hedgerows, and fencerows [19,29]. They are rarely found in swamps or deep forest habitats [28]. Eastern screech-owls generally prefer areas with widely spaced trees interspersed with grassy openings [10]. In Connecticut, red maple woodlands, upland woodland, evergreen hedgerows, and edge habitats were used by eastern screech-owl more often than expected if habitat choice were random. Lawns, mixed woods, and evergreen woods were used less often than would be expected if habitat choice were random. Although lawns were not a selected habitat, they were a major component of all monthly home ranges (a monthly home range is the amount of territory used in the span of a month) [30]. In central Kentucky radio-tagged eastern screech-owls used woodlots and edges more than expected based on availability, and used pastures, old fields, and croplands less than expected [32]. Lynch and Smith [38] reported that eastern screech-owl abundance in Connecticut was positively related to the amount of natural area within urban open space (examples include shrubs, old fields, and marshes). There was also a positive relationship among eastern screech-owl abundance, total habitat diversity, and the amount of linear edge. Areas with mixtures of habitats including relatively high amounts of undisturbed successional communities and edges tended to support many owls [38]. In the southeastern states, eastern screech-owls are found up to 4,500 feet (1,371 m) elevation (but are rare at the higher elevations) [15]. Hunting: Eastern screech-owls usually hunt in grassy openings, fields, meadows, and along wooded field margins and streams [10]. Home Range: In suburban areas most food gathering trips are less than 330 feet (100 m) round trip. In areas with lower prey density food trips may be longer [14]. Home range size is related to prey availability. Smith and Gilbert [30] estimated that the area traversed in one night (the nightly range) for female eastern screech-owls was the largest (38 acres [15.5 ha]) from November to February (when prey was most scarce), was smallest during egg-laying and incubation (13 acres [5.4 ha]) in March and April, and expanded again in June to 22 acres (8.9 ha). The larger nightly ranges in winter were thought to reflect a need to cover greater areas to obtain adequate food. The total home range of one female was 323 acres (130.9 ha), but she typically hunted only a small area each night and a larger cumulative portion each month. Home range was largest while a female was selecting a nest site and smallest during egg laying, incubation, and care of young. The actual defended territory included only the area immediately around the nest cavity [30]. Gehlbach [14] estimated Connecticut home ranges as 9.9 to 14.8 acres (4-6 ha) and Texas home ranges exceeding 74.1 acres (30 ha). Estimated Population Density: In the Southeast, sampled breeding density was listed as 2.8 pairs per 100 acres (2.8 pairs/40 ha) [15]. Lynch and Smith [38] observed a range of 1 to 18 eastern screech-owls per square mile (1-7/sq km); an average of 6 birds per square mile (2.3/sq km) occurred in 4 suburban areas in Connecticut. COVER REQUIREMENTS : Nesting: Eastern screech-owls nest in natural cavities, woodpecker holes, nest boxes, and other artificial structures [9]. Within the oak-hickory forest region, maples, apples (Malus spp.), sycamores (Platanus occidentalis) with natural cavities, and pines with woodpecker holes are preferred [16]. In Louisiana eastern screech-owls chose nest cavities in trees with lianas more often than expected according to availability [24]. Mean minimum diameter of cavity trees is 12 inches (30 cm) [10]. Eastern screech-owls usually choose cavities with openings 3 to 5 inches (7.6-12.7 cm) in diameter. Typically, cavity height is between 5 and 30 feet (1.5-9 m) above ground [5]. Nest cavities are usually reused in successive years [11]. Nest boxes are often reused by the same pair; one female was recorded using the same box 8 years in a row [37]. Roosting: Eastern screech-owls prefer to roost in natural hollows protected from rain and snow, and out of direct sunlight. They avoid hollows used by fox squirrels (Sciurus niger) [7,19]. Roosting hollows are typically 15 to 20 feet (4.5-6 m) and usually less than 40 feet (12 m) above the ground. Roosting cavity openings are about the same size as nest cavity openings [7]. FOOD HABITS : The eastern screech-owl is an opportunistic feeder. Prey species are primarily small rodents, but numerous other animals are consumed [10]. Norberg [25] stated that insects are the major portion of the diet of Megascops owls, but since the eastern screech-owl is sedentary it switches to mammalian and avian prey in winter [37]. The mammalian prey list includes mice and rats (Muridae), shrews (Soricidae), moles (Talpidae), flying squirrels (Glaucomys spp.), chipmunks (Tamias spp.), and bats (Chiroptera). Avian prey includes songbirds, rock dove (Columbia livia), northern bobwhite (Colinus virginianus), ruffed grouse (Bonasa umbellus), American woodcock (Scolopax minor), common snipe (Gallinago gallinago), American kestrel (Falco sparverius), and even other eastern screech-owls [18]. Eastern screech-owls have killed domestic pigeons, hens, and ducks with prandial intent [19]. Other vertebrate prey includes snakes, lizards, frogs, toads, salamanders, and small fish. Invertebrate prey includes many insects, snails, crayfish, spiders, scorpions, millipedes, and earthworms [18]. Even though the prey lists are long, a few species form the main diet. Favored prey includes meadow vole (Microtus pennsylvanicus), white-footed mouse (Peromyscus leucopus), house mouse (Mus musculus), and woodrats (Neotoma spp.) [19]. Snyder and Wiley [31] estimated that year-round prey consumption by eastern screech-owls is 30.7 percent invertebrates, 0.6 percent lower vertebrates, 65.6 percent mammals, and 3.3 percent birds. Seasonal Diet: In Michigan pellet analysis during spring and summer indicated a high proportion of meadow vole, white-footed mouse, crayfish, and small birds in eastern screech-owl diets [7]. Pellet analysis must be interpreted with caution, since many invertebrate prey items do not contribute to pellet formation. In Ohio almost 65 percent of the food items brought to nest boxes were birds, the majority of which were migratory songbirds [37]. Craighead and Craighead's [7] analysis of pellets (Michigan study area) indicated that meadow vole formed the bulk of the eastern screech-owl winter diet. In a year when meadow vole numbers were lower than average, a higher percentage of small birds appeared in pellets. In both years, white-footed mouse were consumed in amounts comparable to those of meadow voles. Other major pellet components were shrews and moles [7]. In Ohio fall and winter diets contained 30 percent birds [37]. Foraging Habits: Eastern screech-owls tend to follow approximately the same hunting route within the territory, tending to visit previously successful sites [5]. They usually forage in a perch-and-pounce manner, taking short flights to capture already-spotted prey. Eastern screech-owls have been observed to take a position near a bat colony and capture bats as they leave the colony [39]. Insects are often caught in flight. Eastern screech-owls also walk on the ground to forage for insects, particularly night-dormant grasshoppers, and wade into shallow water after fish and aquatic invertebrates [18,21,37,39]. PREDATORS : Larger owls prey on eastern screech-owl; the primary predator is the great horned owl (Bubo virginianus), but others include barred owl (Strix varia), great gray owl (S. nebulosa), snowy owl (Nyctea scandiaca), long-eared owl (Asio otus), short-eared owl (A. flammeus), and common barn owl (Tyto alba). Large hawks also take eastern screech-owl, but only rarely since hawks are largely diurnal. Other predators include domestic cat (Felis catus), Mustelids (minks, weasels, and skunks), northern river otter (Lutra canadensis), bobcat (Lynx rufus), and domestic dogs (Canis familiaris). Snakes have killed adult eastern screech-owls (usually because an eastern screech-owl attacked a snake too large to capture easily) but are more commonly nest predators [19]. MANAGEMENT CONSIDERATIONS : Population Status: Census of eastern screech-owl by song playback provides a quick and relatively easy method to obtain accurate numbers [29]. Eastern screech-owl is common in the eastern United States, where it is often the most common raptor [10,29]. Eastern screech-owl population densities vary with the relative proportion of woodland cover in an area [29]. In Connecticut long-term survey data indicated a decline in eastern screech-owl populations in the 1970's and 1980's, possibly as a result of increased habitat fragmentation and conversion of open woods to residential areas [38]. In Ohio the eastern screech-owl population fluctuated during the 30 years prior to 1975, but no long-term trend was apparent in owls studied in suitable habitat. The estimated annual recruitment needed to maintain population size is 2.21 fledglings per nesting pair. Eastern screech-owls have probably increased with the opening up of dense forest but may be threatened by increasing conversion of woods to residential areas [37]. The increase in early successional forest area in the latter half of the twentieth century, largely due to abandonment of agricultural lands, may benefit eastern screech-owls. Management considerations for maintenance of populations include provision of natural and artificial cavities and preservation of woodlots in suburban areas [38]. Recommended size for eastern screech-owl nest boxes: floor 8 inches by 8 inches (20 cm X 20 cm), cavity depth 8 to 10 inches (20-24 cm), and an entrance hole 3 inches (7.5 cm) in diameter [16]. Pesticide Accumulation: In the early 1970's eggshell thinning and DDE and PCB levels in eggs were found to be relatively low for eastern screech-owls. It was suggested that the consumption of rodents (lower trophic levels) prior to egg-laying contributed to the relatively low pesticide loads in eggs. Consumption of birds (higher trophic levels) increased after eggs were incubated, and thus did not contribute to egg pesticide loads [37]. Other pesticides have not been investigated in relationship to eastern screech-owl. Predator-Prey Relationships: As a general rule, predators that are specialized on small rodents tend to destabilize rodent population cycles, whereas generalized predators tend to have a stabilizing effect, sometimes suppressing cycles altogether. The eastern screech-owl is more generalist in its effects on rodent populations [25]. Even though eastern screech-owls sometimes prey heavily on songbirds, they are more likely to help keep rodent and insect populations in check [19]. Orchard owners reported that putting up nest boxes for screech-owls resulted in a decrease in rodent damage to orchard trees [5]. Eastern screech-owls commonly nest in boxes put up for wood ducks (Aix sponsa), American kestrels, squirrels, and purple martins (Progne subis) and will even attempt to nest in mailboxes. Wood ducks often use nest boxes after eastern screech-owls have left the nest; VanCamp and Henny [37] suggested that wood duck nesting success is enhanced by eastern screech-owl presence because owls discourage the usurpation of nest boxes by European starlings (Sternus vulgaris). Mortality Rates and Causes of Mortality: Mortality rate for the eastern screech-owl was estimated as 69.5 percent the first year; eastern screech-owls over 1 year old experience approximately 34 percent annual mortality [37]. Predation accounts for substantial adult mortality [37]. Collision with motor vehicles is also a major cause of mortality. Other causes include shooting (which has become less frequent since legal protection of raptors was enacted), electrocution, collision with windows, or entrapment in buildings, and drowning (apparently these owls take many baths and can become waterlogged and drown in rain barrels) [18]. There is a small amount of sibling cannibalism, usually after accidental injury to a nestling [19]. In Michigan nest loss due to fox squirrels (Sciurus niger), which usually then appropriate the nest hollow, has been observed [7]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Megascops asio
DIRECT FIRE EFFECTS ON ANIMALS : There is no explicit information in the literature on the direct effect of fire on eastern screech-owls. Adult birds are likely to escape fire. Nestlings and eggs may be vulnerable. HABITAT RELATED FIRE EFFECTS : Habitat related fire effects include loss of habitat, change in habitat structure (which may affect both nesting and hunting), and effects on the prey base. In the southeastern states a majority of small mammals thrive in early- to mid-successional habitats which are maintained by fire or other disturbance [41]. Prey vulnerability depends at least partly on vegetation structure. Low, open vegetation makes prey easier to spot, but eastern screech-owls require perches from which to hunt. Fire-caused wounds may increase decay in large trees, making them more likely to develop cavities (either natural or excavated). FIRE USE : NO-ENTRY FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Megascops asio
REFERENCES : 1. Adam, Christopher I. G. 1987. Status of the eastern screech owl in Saskatchewan with reference to adjacent areas. In: Nero, Robert W.; Clark, Richard J.; Knapton, Richard J.; Hamre, R. H., eds. Biology and conservation of northern forest owls: symposium proceedings; 1987 February 3-7; Winnipeg, MB. Gen. Tech. Rep. RM-142. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 268-276. [24601] 2. American Ornithologists' Union. 1957. Checklist of North American birds. 5th ed. Baltimore, MD: The Lord Baltimore Press, Inc. 691 p. [21235] 3. American Ornithologists' Union. 1983. Checklist of North American birds. 6th ed. Lawrence, KS: Allen Press, Inc. 877 p. [21234] 4. Belthoff, James R.; Ritchison, Gary. 1990. Roosting behavior of postfledging eastern screech-owls. Auk. 107(3): 567-579. [13296] 5. Bent, Arthur Cleveland. 1961. Life histories of North American birds of prey. Part 2. New York: Dover Publications, Inc. 482 p. [22362] 6. Call, Mayo. 1979. Habitat management guides for birds of prey. Techical Note 338. Denver, CO: U.S. Department of the Interior, Bureau of Land Management, Denver Service Center. 70 p. [22451] 7. Craighead, John J.; Craighead, Frank C., Jr. 1969. Hawks, owls and wildlife. Dover Edition. New York: Dover Publications, Inc. 443 p. [24517] 8. Cringan, Alexander T.; Horak, Gerald C. 1989. Effects of urbanization on raptors in the western United States. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 219-288. [22381] 9. de la Torre, Julio. 1990. Owls: Their life and behavior. New York: Crown Publishers. 214 p. [24580] 10. DeGraaf, Richard M.; Scott, Virgil E.; Hamre, R. H.; [and others]. 1991. Forest and rangeland birds of the United States: Natural history and habitat use. Agric. Handb. 688. Washington, DC: U.S. Department of Agriculture, Forest Service. 625 p. [15856] 11. DeGraaf, Richard M.; Yamasaki, Mariko; Leak, William B.; Lanier, John W. 1992. New England wildlife: management of forested habitats. Gen. Tech. Rep. NE-144. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 271 p. [19322] 12. Emmerich, John M.; Vohs, Paul A. 1982. Comparative use of four woodland habitats by birds. Journal of Wildlife Management. 46(1): 43-49. [19283] 13. Fitton, Sam. 1993. Screech-owl distribution in Wyoming. Western Birds. 24: 182-188. [24789] 14. Gehlbach, Frederick R. 1986. Odd couples of suburbia. Natural History. 95(6): 56-64, 66. [24945] 15. Hamel, Paul B.; LeGrand, Harry E., Jr.; Lennartz, Michael R.; Gauthreaux, Sidney A., Jr. 1982. Bird-habitat relationships on southeastern forest lands. Gen. Tech. Rep. SE-22. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 417 p. [15423] 16. Hardin, Kimberly I.; Evans, Keith E. 1977. Cavity nesting bird habitat in the oak-hickory forests--a review. Gen. Tech. Rep. NC-30. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 23 p. [13859] 17. Harlow, Richard F.; Guynn, David C., Jr. 1983. Snag densities in managed stands of the South Carolina coastal plain. Southern Journal of Applied Forestry. 7(4): 224-229. [12571] 18. Johnsgard, Paul A. 1988. North American owls. Washington, DC: Smithsonian Institute Press. 295 p. [23301] 19. Karalus, Karl E.; Eckert, Allan W. 1974. The owls of North America (north of Mexico). Garden City, NY: Doubleday & Company, Inc. 278 p. [24579] 20. Kochert, Michael N. 1986. Raptors. In: Cooperrider, Allan Y.; Boyd, Raymond J.; Stuart, Hanson R., eds. Inventory and monitoring of wildlife habitat. Denver, CO: U.S. Department of the Interior, Bureau of Land Management, Denver Service Center: 313-349. [13527] 21. Marshall, Joe T., Jr. 1967. Parallel variation in North and Middle American screech-owls. Monongraphs of the Western Foundation of Vertebrate Zoology No. 1. Los Angles, CA: Western Foundation of Vertebrate Zoology. 72 p. [24944] 22. Marti, Carl D.; Marks, Jeffrey S. 1989. Medium-sized owls. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 124-133. [22382] 23. Mazur, Kurt M. 1992. Fall food of the eastern screech-owl in Manitoba. Blue Jay. 50(1): 33-35. [24788] 24. McComb, William C.; Noble, Robert E. 1981. Nest-box and natural-cavity use in three mid-south forest habitats. Journal of Wildlife Management. 45(1): 93-101. [19257] 25. Norberg, R. Ake. 1987. Evolution, structure, and ecology of northern forest owls. In: Nero, Robert W.; Clark, Richard J.; Knapton, Richard J.; Hamre, R. H., eds. 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