Index of Species Information

WILDLIFE SPECIES:  Bubo virginianus


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

ABBREVIATION : BUVI COMMON NAMES : great horned owl big-eared owl hoot owl cat owl TAXONOMY : The currently accepted scientific name of great horned owl is Bubo virginianus (Gmelin) [38]. The widespread yet sedentary nature of the great horned owl has given rise to a number of races and subspecies, probably due to lack of interbreeding. Accepted subspecies and their common names are as follows [2,24,25]: Bubo virginianus ssp. virginianus (Gmelin), great horned owl B. v. ssp. algistus (Oberholser), St. Michael horned owl B. v. ssp. heterocnemis (Oberholser), Labrador horned owl B. v. ssp. lagophonus (Oberholser), northwestern horned owl B. v. ssp. occidentalis Stone, Montana horned owl B. v. ssp. pacificus Cassin, Pacific horned owl B. v. ssp. pallascens Stone, western horned owl B. v. ssp. saturatus Ridgway, dusky horned owl B. v. ssp. scalariventris Snyder, Ontario horned owl B. v. ssp. subarcticus (Hoy), arctic horned owl B. v. ssp. wapacuthu (Gmelin), tundra horned owl ORDER : Strigiformes CLASS : Bird FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


WILDLIFE SPECIES: Bubo virginianus
GENERAL DISTRIBUTION : The great horned owl breeds from western and central Alaska and central Yukon east to Labrador and Newfoundland and south throughout North and South America to Tierra del Fuego. Winter range is essentially the same except for some migration to the southeast by northern populations, usually in severe winters [14]. 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 FRES20 Douglas-fir FRES21 Ponderosa pine FRES22 Western white pine FRES23 Fir-spruce FRES24 Hemlock-Sitka spruce FRES25 Larch FRES26 Lodgepole pine FRES27 Redwood FRES28 Western hardwoods FRES29 Sagebrush FRES30 Desert shrub FRES31 Shinnery FRES32 Texas savanna FRES33 Southwestern shrubsteppe FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands FRES41 Wet grasslands FRES42 Annual grasslands FRES44 Alpine STATES :

BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : The great horned owl occurs in all Kuchler types. SAF COVER TYPES : The great horned owl occurs in all SAF types. SRM (RANGELAND) COVER TYPES : The great horned owl occurs in most SRM cover types. PLANT COMMUNITIES : Great horned owls occupy a wide variety of forested habitats including open coniferous and deciduous forests, mixed woods, orchards, second growth forests, marshes, swamps, riverine forests, partially wooded slopes, brushy hillsides, farm woodlots, and large city parks [13]. In the western states great horned owls are often found in oak (Quercus spp.) and pinyon (Pinus spp.)-juniper (Juniperus spp.) woodland [40]. In Idaho great horned owls are common wherever trees are large enough for shelter [8]. In west-central Utah great horned owls are permanent residents in pinyon-juniper woodlands [18]. In the Little Missouri National Grasslands of western North Dakota, great horned owls were observed in cottonwood (Populus spp.) woodlands but not in ash (Fraxinus spp.) or juniper types. In this area, cottonwoods were lower in total tree density but had higher canopy coverage than other types. In cottonwood woodlands ground cover was 20 percent, dominated by grasses [20]. In northeastern Wyoming great horned owls occupy riparian areas dominated by eastern cottonwood (P. deltoides) and willows (Salix spp.) surrounded by upland big sagebrush (Artemisia tridendata)-grassland (primarily Agropyron) communities [33]. In Ohio, great horned owls occur in virgin American beech (Fagus grandifolia)-maple (Acer spp.) forests [1]. In the southeastern United States great horned owls are common in baldcypress (Taxodium distichum) swamps and expansive, dense cabbage palmetto (Sabal palmetto)-pine woodlands [13]. Andersen [4] listed the great horned owl as a secondary grassland raptor; it sometimes breeds in grasslands but more typically breeds in woodlands, edge communities, or partly open habitats. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Bubo virginianus
TIMING OF MAJOR LIFE HISTORY EVENTS : Migration: Great horned owls are resident in most parts of their range in North America [32]. Most (93%) banded birds from a wide range of study sites have been recovered within 48 miles (80 km) of the banding location. Great horned owls banded in the South had traveled shorter distances than great horned owls banded in the North [24]. Great horned owls migrate away from conifer bogs and forests in the northern parts of their range in severe winters. It is also common for great horned owls to move from Canada to the northern Great Lakes States in winter [32]. Pair Formation: Great horned owls are usually the earliest nesting raptors. Pair formation occurs in early winter; the male chooses a nest site and attempts to attract a female by copious vocalizations [24]. Nesting: In Maryland and the District of Columbia great horned owls nest from late January to late May; extreme egg dates are January 27 and April 12 [38]. The typical great horned owl clutch is two or three eggs; clutch sizes range from one to six eggs. The male feeds the female while she incubates the eggs. Incubation time is 25 to 30 days [12]. Development of Young: Hatching dates usually occurs in mid-February. The altricial young are downy, with eyes closed. Their eyes usually open by 7 days. Hatchlings are brooded almost constantly by the female for up to 3 weeks. The male parent guards the nest closely. Nestlings often edge out of the nest by about 32 days but remain near the nest and continue to be cared for by the parents until after full flight is achieved. At about 6 weeks of age nestlings begin flapping and learning to fly; first flight may occur by 9 weeks but sustained flight is usually not achieved until about 12 weeks. Fledglings may spend up to 14 days on the ground prior to achieving full flight capability [12,25]. Age at First Breeding: The great horned owl usually first breeds at 2 years of age [25]. Diurnal Activity: In Manitoba juvenile great horned owls were observed hunting between 8 p.m. and 12 a.m. in July and August [7]. Longevity: The oldest banded great horned owl recovered in the wild was 13 years old. Captive birds may live more than 20 years [25]. PREFERRED HABITAT : Great horned owls occupy more diverse habitats than any other owl; habitats harboring great horned owls include deep forests (both coniferous and deciduous), open woodlands, chaparral, desert cliffs, woodlots, and wooded urban environments [12,32]. Great horned owls prefer mature successional stages with openings [32]. Great horned owl habitat usually includes fields and/or wetlands. Recent findings suggest a lower density of great horned owls in heavily forested tracts than in more open areas; for example, there is a lower frequency of great horned owls in the heavily wooded northern third of Wisconsin than in the more open southern two-thirds [32]. In Utah great horned owls were found most frequently in thinned stands. They often forage in slash piles [43]. In Maryland great horned owls are found in forests and woodlots, adjacent fields, and marshes [38]. In New Jersey great horned owls avoid close contact with human habitation and prefer to be near water courses and in upland and lowland hardwoods. In southeastern Wisconsin, an average of 27 percent of the entire annual home range was wooded or in marshlands and wet shrub communities; the remainder varied among open areas and agricultural developments. Actual usage patterns within home ranges were concentrated in areas with appropriate hunting and nesting sites (i. e., perches near open areas) [31,32]. The great horned owl is found from sea level to timberline [13,37]. Home Range: In southeastern Wisconsin the average size of the great horned owl's annual home range was about 813 acres (329 ha). Home ranges of successful breeders were larger. Home ranges decreased for both successful and unsuccessful breeders in spring as prey availability increased. During summer, home ranges gradually expanded again [31]. Petersen [31] reported a density of one pair per 3 square miles (7.5 sq km) in southeastern Wisconsin, but an active breeding density of one pair per 4 square miles (9.3 sq km). Nesting densities of great horned owls in Michigan ranged from 0.15 to 0.26 bird per square kilometer. The average home range was 524 acres (212 ha) [9]. In eastern South Dakota the daily range of great horned owls exceeded observation plot size of 100 acres (40 ha) [16]. Roosting: Great horned owls usually roost in dense foliage, tree cavities, old nests, and crevices in rocks [12]. Nesting: Nest sites are often chosen adjacent to open areas suitable for hunting lagomorphs (Leporidae) and rodents (Rodentia) [13]. In western grasslands, great horned owls were observed in four habitats: unbroken grassland, creek bottoms, cliffs, and cultivated land. The majority of great horned owl observations (80.5%) occurred in creek bottoms [30]. Riparian areas are preferred for nest sites in the northeastern states [28]. Supporting substrates for great horned owl nests included trees (85%), cliffs (9.8%), and creekbanks (4.9%) [30]. In southeastern Wisconsin the number of active breeding pairs of great horned owls was apparently related to cottontail (Silvilagus spp.) density; owl productivity (number of young fledged) was positively related to abundance of staple prey [31]. Hunting: Prey availability in grasslands is a function of prey density, vegetation structure, and mode of hunting. Raptors tend to hunt in areas with high capture probability [4]. In northeastern Colorado great horned owls were observed in grazed bottomlands more often than in ungrazed bottomlands, possibly because the lower vegetation left prey more vulnerable [11]. Sympatry with common barn owls (Tyto alba) is made possible by differing hunting strategies; for example, great horned owls tend to hunt from perches and common barn owls typically capture prey during flight [23]. COVER REQUIREMENTS : Nesting: The great horned owl usually uses nests that were built by other bird species, especially hawks (Buteonidae), herons (Ardeidae), and crows (Corvus spp.) [14], but also common ravens (C. corax), ferruginous hawks (Buteo regalis), and red-tailed hawks (B. jamaicensis). Great horned owls also use nest cavities excavated by pileated woodpeckers (Drycopus pileatus) [18]. In northeastern Wyoming great horned owls use nests of golden eagle (Aquila chrysaetos), ferruginous hawk, red-tailed hawk, and Swainson's hawk (B. swainsonii) [33]. Great horned owl nests are up to 70 feet (21 m) above ground in cavities, tree limb crotches, stumps, caves, and rocky crevices, and on ledges [14,33]. In the Great Basin great horned owls nested in juniper trees, on cliffs, and in abandoned quarries with steep fronts [18]. The great horned owl commonly uses the same territory but a different nest each season. In Wyoming one pair continuously occupied the same territory for 7 successive years and another pair held a territory for 8 years. Great horned owls occasionally reuse the same nest in successive breeding seasons [7]. Roosting: Great horned owls usually roost in places that allow maximum concealment during daylight hours. They often choose trees with dense foliage that are separated from other trees in the area. Conifers are favored when present; in deciduous forests great horned owls prefer trees that hold clusters of dead leaves over the winter (i.e., oaks and American beech) [24]. In urban settings, great horned owls nest in deserted buildings, powerline towers, haylofts of abandoned barns, and artificial nests [10]. Hunting: Great horned owls often hunt from perches adjacent to open areas. They usually fly below the treetops but occasionally fly slightly higher [25]. FOOD HABITS : The great horned owl uses a wide variety of prey and takes animals up to the size of young wild turkey (Meleagris gallopavo) and common porcupine (Erethizontidae dorsatum). Small- to medium-sized mammals and birds are preferred, including hares and rabbits (Leporidae), mice (Muridae), Virginia opossum (Didelphis virginiana), common muskrat (Ondatra zibethicus), squirrels (Sciuridae), pocket gophers (Geomyidae), and voles (Microtus spp.) [12]. Great horned owls also take reptiles (including snakes), amphibians, large insects, and fish [12,14]. In the Sierra Nevada 61 percent of great horned owl diet consisted of cottontails; woodrats (Neotoma spp.) were the second most consumed food item. Pocket gophers and snakes were minor dietary components. In Oklahoma 25 percent of great horned owl diet was cottontails, 18 percent pocket mice (Perognathus spp.), 12 percent kangaroo rats (Dipodomys spp.), and 10 percent grasshopper mice (Onychomys spp.) [40]. Other prey items include skunks (Mephitis and Spilogale spp.), ducks and geese (Anatidae), ring-necked pheasant (Phasianus colchicus), grouse (Phasianidae), domestic chickens, woodpeckers (Picidae), orioles (Icterus spp.), and jays (Corvidae) [12]. Large prey can include small dogs, domestic cats, and young foxes (Vulpes and Urocyon spp.) [10,25]. Predation on songbirds is minimal [12]. In northeastern Wyoming riparian areas and adjacent big sagebrush-grasslands, the prey base for great horned owls consists largely of white-tailed jackrabbit (Lepus townsendii), cottontails, and black-tailed prairie dog (Cynomys ludovicianus). Other mammals and reptiles are common prey items [33]. Hunting Style: Great horned owls usually hunt from a perch at the edge of a clearing, making short flights out to capture prey. They also forage on the wing. On occasion, great horned owls have been observed walking on the forest floor turning over litter and other materials to find insects, mice, and shrews (Soricidae). Great horned owls wade into shallow water for crayfish, fish, frogs, and turtles [24,25]. PREDATORS : Adult great horned owls have no natural routine predators. Antagonistic interactions with red-tailed hawks and crows are common [25]. Crows mob and harass great horned owls during the day; great horned owls attack roosting groups of crows at night, killing many at a time [12]. MANAGEMENT CONSIDERATIONS : Population Stability: The great horned owl is a widespread and common raptor. All the midwestern states report great horned owls as common to abundant, and they are common to abundant in the Great Plains. Most great horned owl populations are currently stable or increasing. Only on the High Plains Border and the Unglaciated Missouri Plateau physiographic provinces did Breeding Bird Survey data suggest declining populations [32]. Nesting densities and territory sizes fluctuate annually, probably due to changes in food supply. In Wyoming a particularly small nesting population was observed in the same year that cottontail populations were unusually low. Temporary declines in prey base are unlikely to cause any long-term great horned owl population perturbations since great horned owl pairs unsuccessful breeders one year are often successful in other years [34]. Only the most general raptor management considerations need to be made for great horned owls, such as retention of cavity trees, protection of riparian woods within grasslands, and protection from human harassment [30,33]. Forest Composition: In the northeastern United States, woods consisting of hardwoods and pines are good habitat for great horned owl and other raptors (barred owl [Strix varia], northern goshawk [Accipiter gentilis], broad-winged hawk [Buteo platypterus], and red-tailed hawk). Forest unit management guidelines should be set in relationship to selected home range size; since the great horned owl has a very large home range, managers should consider forest composition objectives in groups of units rather than individual units. All cavity trees and at least 10 percent of remaining forest cover should be mature and/or decadent trees. Silviculture treatments favoring raptors in the White Mountain National Forest, New Hampshire, included one 0.25- to 0.5-acre (0.1-0.2 ha) plot left uncut for every 10 acres (4 ha) cut in regeneration plots. Uncut areas contained at least one living tree 18 inches (45.7 cm) or more in diameter with at least two major defects. Wherever possible, uncut areas included existing raptor nests (any species, since great horned owls use old nests of other raptors) [28]. Similarly, in Utah wildlife management considerations included leaving large old trees for cavity nesters. Woyda and Kessler [43] were of the opinion that harvest patterns that result in even-aged regeneration would only be appropriate for great horned owl and other species that do not require a variety of tree age classes. Young [44] lists the great horned owl as capable of persisting in agricultural areas; nesting densities are strongly influenced by intensity of land use, agricultural practices, and human activity. Winter use of agricultural areas by great horned owls is common [44]. Artificial Nests: Great horned owls use artificial nests when more suitable nest sites are unavailable. However, adding artificial nest and perch sites in grasslands may encourage the use of grasslands by woodland and edge species at the expense of raptors that primary use grasslands [4]. Urban Settings: Wintering great horned owl density reflects availability of medium-sized prey such as skunks, domestic cats, etc. [10]. Mortality: Major causes of death for great horned owls include collisions with vehicles, shooting, and starvation [24,32]. The highest mortality rates are among juveniles, largely due to cannibalism and severe weather; annual mortality rate was 15 percent for nestlings, 58 percent for juveniles, 44 percent for 1- to 2-year-olds, and 28 percent for adults over 2 years old [24,25]. At least 52 percent of banded and recovered great horned owls had been shot and 12 percent had been trapped; perhaps as many as 96 percent had been killed intentionally [24]. Mortality due to pesticides during 1946 to 1968 was minimal [32]; however, poisoning of great horned owls due to pesticides used in urban and suburban environments has been increasing [12]. Nuisance: The majority of respondents to a raptor nuisance survey (33/54) reported great horned owl nuisance, damage, or safety problems. Most reported problems involved predation at poultry and game farms, and at beagle clubs (preying on domestic rabbits kept for club activities). Other nuisance problems involved predation on pets including exotic animals and birds [21]. Raptor Reintroduction Projects: Great horned owl presence at peregrine falcon (Falco peregrinus) release sites is detrimental to the survival of nestling and juvenile peregrine falcons. Great horned owls occupy suitable peregrine falcon nest sites (which are usually scarce) and prey on juvenile great horned owls. Much debate has occurred over the feasibility and necessity for great horned owl removal during peregrine falcon reestablishment. The intent of most great horned owl removal have been to reduce the threat to young peregrine falcons immediately after release. Personnel at the U.S. Fish and Wildlife Service have stated that great horned owl control is unnecessary once falcons are established and reproducing (with naturally fledged peregrine falcons present). They do, however, support localized great horned owl control for a few months after peregrine falcon release and/or fledging [22]. Similar problems pertain to prairie falcon (F. mexicanus) management; most nest sites large enough for prairie falcons are also suitable for great horned owls, and young prairie lafcons are vulnerable to predation by great horned owls [30]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Bubo virginianus
DIRECT FIRE EFFECTS ON ANIMALS : Direct impacts of fire on great horned owls include loss of nestlings, nest trees, roost sites, and foraging areas; severe fire can result in local loss of preferred habitat [29]. Great horned owl populations are probably minimally affected by even large fires, as this owl has nonspecific habitat requirements and moves to unaffected sites. HABITAT RELATED FIRE EFFECTS : The effects of fire on prey species are probably the most important habitat related fire effects on great horned owls. Prey availability is often enhanced by removal of surface cover. Decreases in prey populations after fire probably result in lowered nesting success or even a change in residency for great horned owls. In California, great horned owl density was high following a fire in chaparral, but reproductive success decreased later, possibly because loss of habitat concentrated raptors into a smaller area and led to increased competition for prey [42]. FIRE USE : Great horned owls use but are not limited to the following fire dependent ecosystems: Presettlement Fire Regime ______________________________________________________________ Habitat Average Fire-Free Interval grasslands 1-5 years semidesert grass-shrub up to 10 years sagebrush (Artemisia spp.)-grass 20-100 years chaparral 20-40 years pinyon-juniper 10-30 years ponderosa pine (Pinus ponderosa) 5-10 years Douglas-fir (Pseudotsuga menziesii) 100-500 years redwood (Sequoia sempervirens) 17-82 years giant sequoia (Sequoiadendron gigantea) 5-10 years Fire exclusion has had more detrimental effects than benefits on raptor habitat. Prescribed fire in raptor habitats usually does not conflict with raptor habitat objectives and can in many cases be beneficial [29]. REFERENCES : NO-ENTRY


WILDLIFE SPECIES: Bubo virginianus
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