Strix nebulosa



INTRODUCTORY


  Photo courtesy of Dave Herr

AUTHORSHIP AND CITATION:
Ulev, Elena D. 2007. Strix nebulosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
STNE

COMMON NAMES:
great gray owl
great grey owl
great cinereous owl
Lapland owl
Siberian owl
sooty owl
speckled owl
spectral owl

TAXONOMY:
Strix nebulosa (Forster) is the scientific name for the great gray owl, a member of the Strigidae family [1,4,90]. Listed below are the 2 recognized subspecies [2,4,90]:

Strix nebulosa nebulosa (Forster)
Strix nebulosa lapponica (Thunberg)

SYNONYMS:
None

ORDER:
Strigiformes

CLASS:
Bird

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state-level protected status of animals in the United States is available at NatureServe, although recent changes in status may not be included.

ANIMAL DISTRIBUTION AND OCCURRENCE

SPECIES: Strix nebulosa
GENERAL DISTRIBUTION:
The great gray owl is a native, permanent resident of the boreal forests of North America and Eurasia [27,53,59,75]. Strix nebulosa nebulosa inhabits North America and S. n. lapponica inhabits Eurasia [27,53]. Bird Web provides a distributional map of the great gray owl in North America, as well as photos.

The great gray owl is unevenly distributed and variable throughout its North American range [27]. Information on population status is currently lacking in many geographic areas [11,22,38,53].

The known breeding range in North America is from the boreal forests of Alaska east to Ontario and south to northern Minnesota and Wisconsin [3,4,28,53]. Great gray owls also breed in northern Idaho, western Montana, northwestern Wyoming [3,48], northeastern Utah [3,28], west-central Nevada [53], and the Sierra Nevada [3,48].

The wintering range is generally the same as the breeding range, except for a tendency for great gray owls to wander south in search of prey [27,68,100]. Great gray owls may wander to southern Canada, [4,69], New England, New York, and northern Michigan [69].

The following lists are speculative and are based on the habitat characteristics and species composition of communities great gray owls are known to occupy. There is not conclusive evidence that great gray owls occur in all the habitat types listed, and some community types, especially those used rarely, may have been omitted. See Preferred Habitat for more detail.

ECOSYSTEMS [45]:
FRES10 White-red-jack pine
FRES11 Spruce-fir
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
FRES28 Western hardwoods
FRES29 Sagebrush
FRES37 Mountain meadows
FRES40 Desert grasslands
FRES44 Alpine

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES
AK CA ID MN MT NV OR UT WA WI
WY

CANADA
AB BC MB NT NS ON PQ SK YK

BLM PHYSIOGRAPHIC REGIONS [17]:
2 Cascade Mountains
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin

KUCHLER [62] PLANT ASSOCIATIONS:
K002 Cedar-hemlock-Douglas-fir forest
K004 Fir-hemlock forest
K005 Mixed conifer forest
K007 Red fir forest
K008 Lodgepole pine-subalpine forest
K010 Ponderosa shrub forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K014 Grand fir-Douglas-fir forest
K015 Western spruce-fir forest
K026 Oregon oakwoods
K028 Mosaic of K002 and K026
K030 California oakwoods
K052 Alpine meadows and barren
K093 Great Lakes spruce-fir forest
K094 Conifer bog
K095 Great Lakes pine forest
K098 Northern floodplain forest
K099 Maple-basswood forest
K101 Elm-ash forest
K106 Northern hardwoods
K107 Northern hardwoods-fir forest
K108 Northern hardwoods-spruce forest

SAF COVER TYPES [39]:
1 Jack pine
5 Balsam fir
12 Black spruce
13 Black spruce-tamarack
14 Northern pin oak
15 Red pine
16 Aspen
21 Eastern white pine
27 Sugar maple
38 Tamarack
39 Black ash-American elm-red maple
63 Cottonwood
107 White spruce
201 White spruce
202 White spruce-paper birch
203 Balsam poplar
204 Black spruce
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
207 Red fir
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
17 Aspen
218 Lodgepole pine
224 Western hemlock
227 Western redcedar-western hemlock
228 Western redcedar
229 Pacific Douglas-fir
230 Douglas-fir-western hemlock
233 Oregon white oak
234 Douglas-fir-tanoak
237 Interior ponderosa pine
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
247 Jeffrey pine
251 White spruce-aspen
252 Paper birch
253 Black spruce-white spruce
254 Black spruce-paper birch
256 California mixed subalpine

SRM (RANGELAND) COVER TYPES [89]:
108 Alpine Idaho fescue
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
213 Alpine grassland
215 Valley grassland
216 Montane meadows
409 Tall forb
410 Alpine rangeland
411 Aspen woodland
920 White spruce-paper birch

PLANT COMMUNITIES:
See lists above.

BIOLOGICAL DATA AND HABITAT REQUIREMENTS

SPECIES: Strix nebulosa

 

  Photo courtesy of David McCann
TIMING OF MAJOR LIFE HISTORY EVENTS:
Migration: Great gray owls may be resident or seminomadic, depending on the availability of rodent prey [59,68,69,100]. They may move to low elevations during winter to avoid hunting in deep snow [43].

Mating: Great gray owls are generally not monogamous; however, pair bonds may be maintained in boreal forests if prey populations remain high over subsequent years [37]. Great gray owls probably first breed when 3 years old [22,23]. Pair formation begins in January and extends as late as 2 weeks before egg-laying in April and May [43].

Nesting: Nesting chronology data for the great gray owl are meager. Timing of egg laying may depend on the availability of rodent prey and habitat quality [100]. Egg laying may be delayed during years of heavy snow [43]. In California, great gray owls nest in April [106]. Egg laying occurs in April and May in southeastern Idaho and northwestern Wyoming [43]. In northern Alberta, the earliest egg-laying date was 23 March, but most eggs were laid by 15 April [76].

Eggs are laid at 1- to 3-day intervals [27]. Clutch size ranges from 2 to 5 eggs, and 3-egg clutches are most typical [76]. Average clutch size was 2.67 (n=6) eggs in the Targhee National Forest, Idaho [103] and 2.3 eggs (n=64, SD=0.87) in northeastern Oregon [23].

Incubation is performed only by the female [27,76], and brooding lasts 2 to 3 weeks [27,76]. Brooding lasted an average of 29.7 days in southeastern Idaho and northwestern Wyoming [43].

Development: Great gray owls are semiprecocial and nidicolous [27]. Adults may sometimes favor their smaller or weaker offspring [23].

Fledging: Young leave the nest 26 days [23] to 28.5 days [43] after hatching. Owlets learn to fly 7 to 14 days after leaving the nest. Before learning to fly, they climb leaning trees using their talons, wings, and bills, and roost off of the ground [28,43]. Females continue protecting their young after fledging and males bring prey items. Males may extend fledgling care longer than females. In Oregon, females abandoned their young between 3 and 6 weeks after fledging, but males provided care for up to 3 months after fledging [28]. Young are independent by late summer and leave the natal site in fall and winter. Maximum dispersal distance of radio-tagged juvenile great gray owls from their natal site in Oregon ranged from 4.7 to 19.9 miles (7.5-32.0 km) [24].

Survival: The survival of young depends on the availability of leaning and deformed trees as well as the presence of forested habitat within a 1,640- foot (500 m) radius around the nest for roosting and avoiding prey [43]. Owlets have a 63% chance surviving from the egg to the flight stage [43]. In northeastern Oregon, the probabilities of juveniles surviving to the following ages were: 12 months old=0.53; 18 months old=0.39; and 24 months old=0.31 (n=32). Mortality was due to starvation, falling from the nest [28], or predation) [23]. Survival rates are high if juveniles survive to breeding age [28].

Home range: The home range of 5 nesting males in northeastern Oregon averaged 4.5 kmē (range 1.3-6.5 kmē) [24].

PREFERRED HABITAT:
General: Great gray owls occur in a wide range of habitats and elevations [40] but prefer forest and meadow associations across their range [11,21,57,59,100]. Great gray owls are flexible in their use of habitats [22,25]. During winter, they may leave areas with deep snow to find prey more easily. In northeastern Oregon, they are somewhat nomadic, opportunistic, and versatile, and are not associated with a particular area year-round [24].

Elevations of 6,000 to 9,000 feet (1,830-2,740 m) are utilized most often in southern portions of the great gray owl's range [57,106]. In the Manitoba escarpment, the mean elevation of great gray owls was 2,101 feet (ą193.6) (640.4 m) (ą59.0 m) [56].

Breeding: Mature and old-growth coniferous and deciduous forests [22,52,61,63] with a high density of snags [11] are preferred for breeding. Forest patches used for nesting do not need to be large but must occur frequently throughout a landscape [52]. In the Sierra Nevada, mixed-conifer and red fir (Abies magnifica) forests are used for breeding [59]. In the midwestern United States, dense coniferous and deciduous forest, especially pine (Pinus spp.), paper birch (Betula papyrifera), and balsam poplar (Populus balsamea), are preferred [61]. In Canada, great gray owls breed in taiga interspersed with muskegs and sphagnum bogs [88].

Snags >3 feet (1 m) are very important to the breeding and foraging needs of the great gray owl [86].

In south central Oregon, 95% of sites with great gray owls occurred within 0.2 mile (0.3 km) of a meadow; the remainder occurred 0.2 to 0.5 mile (0.3-0.8 km) from a meadow. Meadow size ranged from 6 ha to more than 100 ha, and meadows contained grasses, herbaceous vegetation, sagebrush, and rock. All were "relatively wet" during spring. All great gray owls were found in stands with relatively large overstory trees; 71% of owl locations were in old growth (>70 years old for lodgepole pine and >200 years old for other types). Nearly all great gray owl locations (94%) were dominated by lodgepole pine or a mixture of lodgepole and ponderosa pine. The majority of sites (70%) had been selectively logged or used for firewood cutting within 20 years of the study but still contained areas of "fairly dense forest" [21].

Nesting: Nest site availability may be a critical factor regulating the population size of great gray owl [27].

Nesting occurs within mature and old-growth coniferous and deciduous forests [22,24,25,43,52,61,63]. In northeastern Oregon, 4 forest types were used by great gray owls for nesting. Seventy-four percent of nests occurred in trees 19 inches (>49 cm) DBH; 26% occurred in trees 12 to 16 inches (30-40 cm) DBH; and 0% in trees <12 inches (30 cm) DBH. For details about the habitat characteristics for 46 great gray owl nests including forest type, successional stages, frequency of logging, and percent canopy closure, see Bull and Henjum [28] and Bull and others [25]. In Alberta, nests were located close to grassy agricultural fields due to an abundance of common voles (Microtus pennsylvanicus) [93].

Nest sites used by great gray owls are generally rare elements in most forest stands [52]; however, great gray owls are opportunistic regarding nest selection and use any available nest type [27,38,103]. Nest types include large, broken-top trees, trees with large dwarf mistletoe (Arceuthobium spp.)-induced witch's brooms [76], old tree stumps [76,93], and vacated bird nests [28,52,73,76,100].

In Yosemite National Park, great gray owl nests were found only in large, broken-top trees [105]. Mistletoe brooms [11,28,43,78,103,106] used by the great gray owl are commonly located in Douglas-fir (Pseudotsuga menziesii) [28] or western larch (Larix occidentalis) trees [78]. Great gray owls may compete with great horned owls (Bubo virginianus) for nest sites, since neither species builds its own nest [100]. Vacated stick nests [11,28,43,73,76,100,103] of northern goshawks (Accipiter gentilis) [73,76,100,103], red-tailed hawks (Buteo jamaicensis) [100,103], broad-winged hawks (B. platypterus), American crows (Corvus brachyrhynchos), common ravens (Corvus corax) [73,76,100], and osprey (Pandion haliaetus) [76,100] are used. The ratio of snag to stick nests depends on latitude. Stick nests are more common at high latitudes, and snag nests are more common in low latitudes. This may be due to nest-site availability in different areas of the species's breeding range [43]. Great gray owls use old western gray squirrel (Sciurus griseus) nest most frequently in oak (Quercus spp.) woodlands of the Siskiyou Mountains in southeastern Oregon [40].

Human-made nesting platforms have been successfully used by great gray owls [28,43]. Nest success on artificial platforms built in Oregon was 88%, compared to 66% at natural nesting sites [28] (see Management Considerations).

Three great gray owl nests found on the Willamette National Forest in Oregon were in broken-top Douglas-firs. Nest trees were 35 to 50 inches (90-128 cm) in DBH and 34.1 to 104.7 feet (10.4-31.9 ft) tall, with canopy cover around nest trees ranging from 25% to 65% [46].

Foraging: Great gray owls prefer natural forest openings such as meadows, bogs, fens, muskegs, and peatlands for foraging g[11,20,21,22,51,57,72,93,106]. Subclimax, old-growth, selectively logged, and small clearcut forests are also used for foraging, but not as often as natural forest openings [11,25,106]. Great gray owls typically hunt from perches close to the ground. They need suitable foraging habitat 0.6 to 1.9 miles (1.0-3.0 km) from their nest [28,53]. In northeastern Oregon, males foraged a maximum of 0.4 to 2.0 miles (0.7-3.2 km) from the nest. Great gray owls may leave areas with >20 inches (50 cm) of snow to locate and plunge for prey more easily [28].

Perching and roosting: Perches are used for hunting, regurgitating pellets, defecating, and hiding. Perch sites include tree branches, downed woody material, tops of trees, tree stumps [28,29], posts, power lines, and telephone poles [100]. In northeastern Oregon, nesting female great gray owls used branches (61%), leaning trees (26%), and broken-topped snags (13%) of ponderosa pine, lodgepole pine, and western larch snags for perching [28]. Perches were usually <20 feet (6 m) from the ground and located in forest with an open understory and 59% mean canopy cover. Perch height averaged 7 to 16 feet (2-5 m) from the ground, and great gray owls moved from perch to perch if no prey was found. When prey was found, they hovered over it before pouncing quickly [27], and sometimes plunged several centimeters into the snow [73]. Average perch to prey distance in northeastern Oregon was 34.5 feet (10.5 m) [28].

Owlets cannot fly for 2 weeks after leaving the nest and need mature forests containing leaning trees for climbing and perching [25,28,103]. Leaning trees are easiest to climb at first, then large, upright trees with deeply fissured bark are used several days later [25,28,43]. Owlets typically perched 49 feet (15 m) away from natural forest openings and clearcuts on the Targhee National Forest in eastern Idaho and northwestern Wyoming [103]. Forest edges provide most great gray owl hunting perches [106]. For more details about macrohabitat features, tree canopy cover, and distance from perches to forest edges for the great gray owl on the Targhee National Forest in eastern Idaho and northwestern Wyoming, see Whitfield and Gaffney [103].

Territory/density: Great gray owl density may be influenced by nest site availability and/or food supply [28]. Mutually exclusive territories are not maintained, and pairs may nest within 0.3 mile (0.5 km) of each other [24,25]. Nesting densities have been reported at 0.66 pair/kmē in California [106], 0.74 pair/kmē and 1.72 pairs/kmē in Oregon [28], 0.66 pair/kmē [106] and 1.88 pairs/kmē in Minnesota [37], and 1.88 pairs/kmē in Manitoba [37].

Home range: In northeastern Oregon, average home range size for adults was 67.3 kmē [24].

Home ranges for female and male great gray owls in Yosemite National Park, California, were larger than any other population studied in North America. Summer and winter home ranges were [97]:

Home range (ha)

  Females Males
Summer 61.47 19.89
Winter 2457.27 2112.87

Landscape: In northeastern Oregon, nesting males foraged in mature ponderosa pine or Douglas-fir stands with 11% to 59% canopy cover [25]. In the Targhee National Forest in eastern Idaho and northwestern Wyoming, the dominant tree species in great gray owl breeding areas were Douglas-fir and lodgepole pine [103].

After owlets learn to fly, their movements are restricted to forests with >60% canopy cover, perhaps to prevent predation. During the day, 71% of adult males in northeastern Oregon roosted in stands with 11% to 59% canopy closure. Twenty-nine percent used forest with >59% canopy closure [25,28].

FOOD HABITS:
Food supply may be a critical factor regulating the population size of the great gray owl [27].

Diet: Primary foods eaten are small mammals, especially rodents such as voles (Microtus spp. and Clethrionomys spp.), mice (Peromyscus spp.), and pocket gophers (Thomomys spp.) [22,23,37,40,43,46,77,100,106]. Other prey items include shrews (Soricidae) and birds [37]. When desperate for food, great gray owls may eat frogs (Ranidae, Hylidae) [74].

In California, the diet of the great gray owl shifts between microtine rodents and pocket gophers as prey abundance changes [106]. Even when pocket gophers are abundant, great gray owls will not breed in the absence of microtine rodents. This may be due to the difficulty of catching pocket gophers [106].

PREDATORS:
Predators for adult great gray owls include common ravens, great horned owls [23,76,103], northern goshawks [23], broad-winged hawks, and American martens (Martes americana) [103]. Owlets may be killed by red-tailed hawks [28], American black bears (Ursus americanus) [37,76], fisher (Martes pennanti) [37,100], lynx (Lynx canadensis) [37], great horned owls [37], and golden eagles (Aquila chrysaetos) [100].

Other causes of mortality: At least 20% of adult great gray owl mortality is due to starvation during winter [100]. Collisions with vehicles and shooting by humans also cause mortality [103].

MANAGEMENT CONSIDERATIONS:
Forest management practices impact great gray owl populations [38]. On the Salmon National Forest in Idaho, the great gray owl is an indicator species for healthy old-growth forests [57]. Because great gray owls occur in local concentrations, management is recommended in areas where they have been seen in the past or in prime great gray owl hunting habitats characterized as forest edges or meadows with deep soils [28,47].

Management of great gray owl habitat includes protecting nest sites and surrounding habitat, restricting activity around nest sites during the breeding season, retaining stands near foraging areas, and installing artificial nest platforms [42,106]. Artificial nesting platforms placed 30 to 49 feet (9-15 m) from the ground have been used successfully by the great gray owl in Oregon and California [16,28,29]. For detailed building instructions, see Bull and others [29]. Depressions cut into tree stumps make nest sites [30].

Duncan's [38] management recommendations include collecting occurrence data, limiting clearcutting area size to <10 ha within a mosaic of different aged forest stands, clearcutting in irregular shapes such as scalloped-shaped edges to reduce great gray owl predation, and leaving large-diameter dead trees for nest sites and perches [38].

According to Gould [47], management of the great gray owl "should follow in the steps of the spotted owl (Strix occidentalis)" due to similar habitat requirements. This includes managing for large-diameter trees in closed-canopy forest [98].

For general management recommendations and survey techniques for the great gray owl, see the Bureau of Land Management's Survey and Management Recommendations and the Forest Service's Management and Standards Guidelines.

Population trends: Nest site availability, suitable foraging habitat [42,53], and fluctuating rodent prey populations [42] are the most important factors limiting great gray owl populations [53]. Currently, no data substantiate historical population trends in great gray owl distribution [42,48,53], and a standardized survey protocol needs to be developed to determine long-term (>10 years) population trends [38,48,53]. Great gray owl populations in North America are believed to have been stable [27,28,106] for the previous 10 to 100+ years [38]. The population of great gray owls in south-central Oregon is probably declining due to habitat loss from timber harvest, urban sprawl into prime great gray owl areas, and mountain pine beetle (Dendroctonus ponderosae) infestations [21]. In 1987, Duncan [38] estimated that North American great gray owl populations ranged between 20,000 and 70,000 breeding pairs. These numbers reflect the dependence on microtine rodents, which exhibit population fluctuations over 3 to 5 year periods [38].

To sustain a viable population, 30 pairs of great gray owls are needed on the Salmon National Forest in Idaho, requiring a minimum total amount of 50,000 acres (1,670 acres/pair) of old-growth forest [57].

Silviculture: Timber harvest has great impact on the great gray owl. This species requires specific habitat management to persist [48], and monitoring the effects of forest fragmentation is critical [93].

Intensive logging limits the number of nesting, perching, and roosting sites, and can be detrimental to great gray owl populations [22,27,38]. Great gray owl management guidelines emphasize the connectivity of old-growth forest as dispersal corridors [83]. Great gray owl populations may persist with "some amount" of logging [38]. Partial cuts are generally suitable for foraging; however, dead and downed material should be left to increase cover for great gray owl prey such as voles. For natural nests, dead, broken topped trees [31,94] >20 inches (50 cm) DBH should be retained, as well as any tree with old raptor nests, especially northern goshawk nests [28].

Downed wood is important in great gray owl habitat. In northeastern Oregon, downed wood was within 3 feet (1 m) of where prey was caught or attempted to be caught 80% of the time [28]. For detailed recommendations on managing trees and logs in the Interior Columbia River Basin, see Bull and others [29].

Clearcutting may increase the amount of viable foraging habitat for the great gray owl; however, it decreases nesting habitat quality. Clearcutting creates "temporary meadows" capable of supporting rodent populations consumed by the great gray owl, but these meadows undergo "rapid" succession to forests [51]. In southeastern Idaho and northwestern Wyoming, northern pocket gopher (Thomomys talpoides) populations increased in great gray owl diet proportionally to the amount of clearcut forest [43].

Clearcutting decreases the number of mature, large-diameter trees needed for nesting by the great gray owl, which could lead to a decline in great gray owl populations [46,51]. On the Targhee National Forest in eastern Idaho and northwestern Wyoming, great gray owl presence was related to the amount of clearcutting. Areas clearcut 39% to 62% (SD=11.68) did not contain great gray owls. Areas clearcut 14% to 26% (SD= 5.124) contained successful nesting in 2 locations [103].

Dwarf mistletoe: Trees infected with dwarf mistletoe are important nesting sites for great gray owl [28,43,78,103] (see Preferred Habitat). Bull and others [30] suggest that to manage forests containing dwarf mistletoe, choose groups of lightly-infected trees, where the brooms are large and dense enough for animals to build or use an existing nesting platform. Preserve old, infected larch trees when managing for western larch, because they produce high-quality snags sought by wildlife [30].

Agriculture and livestock grazing: Great gray owl nesting density is strongly influenced by the intensity of land use, including agricultural practices and human activity [107]. According to Young [107], the great gray owl is capable of persisting in agricultural areas. Livestock grazing may be harmful, however [32]. The great gray owl may abandon meadows that are heavily grazed by cattle and domestic sheep due to the reduction of rodent prey populations in grazed areas [106].

FIRE EFFECTS AND USE

SPECIES: Strix nebulosa
DIRECT FIRE EFFECTS ON ANIMALS:
As of 2007, no research directly investigated great gray owl mortality due to fire. The direct impact of fire on birds is a function of the bird's size and mobility as well as the characteristics of the fire. Fire may kill great gray owls [79], but mortality is generally minor for adult birds of most species [65,85]. Mortality of nestlings or fledglings is possible if fires occur during the breeding season, so adult birds may experience reduced reproduction rates [79]. Severe fires may result in proportionately greater mortality [82].

HABITAT-RELATED FIRE EFFECTS:
As of this writing, no information is available on the effects of fire on the great gray owl. Despite the lack of information, some generalizations based on their habitat requirements may be possible. Following fire, modifications in the food supply and habitat of great gray owls may occur, as well as changes in the abundance of competitors and predators [85]. According to Finch and others [41], the effects of fire on birds and their habitat vary with: 1) the severity and extent of the fire; 2) temporal scales; 3) life history characteristics of the bird species; and 4) whether or not salvage logging occurs following fire. Severe fires alter the forest structure more than low-severity fires, and a stand-replacing fire may result in the replacement of a bird species with a different bird species. Large, severe fires may greatly alter bird habitat in the short term but be necessary for long-term maintenance of some forest types. Salvage logging may reduce the benefits of fire to birds that utilize snags for foraging and nesting [58]. Prior to European settlement, Native Americans managed forests that provided great gray owl habitat by frequent understory burning. With fire exclusion, habitat for the great gray owl has become less suitable due to decreased forest structure diversity and the encroachment of conifers into meadows [19].

Great gray owls require mature and old-growth forests for breeding and natural forest openings for foraging [21,22,22,51,52,57,63,72,93,106]. On the forest floor, downed woody material and tree stumps are used by adults for perching [28,29]. Leaning trees are needed by owlets for roosting and perching before they learn to fly [25,28,43] (see Preferred Habitat). The availability of nesting sites, perching sites, and foraging habitat are greatly affected by natural forest disturbances such as fire, succession, and disease outbreaks [38]. In the boreal mixed woodland on the plains of Alberta, habitat would probably not be suitable for 25 years after stand-replacing fire [87].

Fire may reduce conifer invasion in natural forest openings [51]. Golden eagles in the Appalachian Mountains stopped breeding after open habitats in the mountains, which were required for foraging, reverted to brush following fire exclusion [92]. Fire exclusion in great gray owl foraging habitat may have a similar effect.

The spotted owl and great gray owl share similar habitat requirements such as large trees, snags, closed canopies, and multiple forest layers. Fire management strategies for the spotted owl may apply to the great gray owl [98]. A fire management suggestion made by the US Department of the Interior, Fish and Wildlife Service [96] and Rapp [83] for spotted owls was to isolate nesting sites from adjoining forest at high risk for fire by creating a buffer zone around sites to reduce flammability. This should be done without compromising the nest site. Verner and others [98] suggest low-severity underburning in spotted owl habitat in the Sierra Nevada, minimizing the removal of duff and large woody debris.

Effects on prey: Rodents use dead woody material on the forest floor and in forest openings for cover [26,28] and may either be positively or negatively affected by fire, depending on fire severity [28,60]. Immediately following prescribed fire in meadows, the availability of prey species increases for the great gray owl due to the removal of grass layers used for cover [10,67]. After the availability of prey increases following fire, prey populations may decrease due to lack of cover [28].

Shrews, deer mice (Peromyscus maniculatus), creeping voles (Microtus oregoni), and Townsend's chipmunks (Neotamias townsendii) were absent to rare on severely burned sites but comprised most of the small-mammal community in unburned clearcuts. The study was conducted following the Oxbow Fire, a large (170 kmē), mixed-severity wildfire in a Douglas-fir and mixed-conifer forest in western Oregon [104]. Rodent populations slowly after the fire, and population numbers were similar between burned and unburned areas by postfire year 7 [18]. Populations of pocket gophers (Thomomys talpoides and T. mazama) generally increase following stand-replacing fire [13], particularly in lodgepole pine/western needlegrass (Achnatherum occidentale) communities in central Oregon. This may be due to the abundance of long-stolon sedge (Carex inops), a rhizomatous, fleshy-rooted graminoid that increases 200% to 400% following burning [99].

The following table provides fire return intervals for plant communities and ecosystems where the great gray owl is important. For further information, see the FEIS review of the dominant plant species listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
grand fir Abies grandis 35-200 [6]
maple-beech-birch Acer-Fagus-Betula spp. >1,000
sugar maple Acer saccharum >1,000
sugar maple-basswood Acer saccharum-Tilia americana >1,000
black ash Fraxinus nigra <35 to 200 [101]
tamarack Larix laricina 35-200 [80]
western larch Larix occidentalis 25-350 [7,15,35]
Great Lakes spruce-fir Picea-Abies spp. 35 to >200 [36]
Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to >200 [6]
black spruce Picea mariana 35-200
conifer bog* Picea mariana-Larix laricina 35-200 [36]
jack pine Pinus banksiana <35 to 200 [34,36]
Rocky Mountain lodgepole pine* Pinus contorta var. latifolia 25-340 [14,15,95]
Sierra lodgepole pine* Pinus contorta var. murrayana 35-200
Jeffrey pine Pinus jeffreyi 5-30
western white pine* Pinus monticola 50-200
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [6]
interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [6,12,64]
red pine (Great Lakes region) Pinus resinosa 3-18 (x=3-10) [33,44]
red-white pine* (Great Lakes region) Pinus resinosa-P. strobus 3-200 [34,54,66]
eastern white pine Pinus strobus 35-200 [101]
eastern cottonwood Populus deltoides <35 to 200 [80]
aspen-birch Populus tremuloides-Betula papyrifera 35-200 [36,101]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [6,49,70]
mountain grasslands Pseudoroegneria spicata 3-40 (x=10) [5,6]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [6,8,9]
coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [6,71,84]
California oakwoods Quercus spp. <35
Oregon white oak Quercus garryana <35 [6]
California black oak Quercus kelloggii 5-30 [80]
western redcedar-western hemlock Thuja plicata-Tsuga heterophylla >200
mountain hemlock* Tsuga mertensiana 35 to >200 [6]
*fire return interval varies widely; trends in variation are noted in the species review

FIRE USE:
A 1989 analysis of western raptor habitat concludes: 1) properly managed prescribed fires and wildfires are necessary within raptor habitat; 2) fire exclusion has led to ecosystem stagnation and will ultimately lead to "devastating" wildfires; 3) prescribed fire can be used to reduce fuels, maintain historic conditions in an ecosystem, and create mosaics of open and closed habitat, thus increasing raptor carrying capacities as well as prey abundance; and 4) unless vegetation types are very similar, it will be difficult to standardize fire management practices [65].

As of 2007, there was no research on the effects of wildfire or prescribed burning for the great gray owl. Data are needed to make detailed management recommendations. Based on the habitat requirements for the great gray owl, fire management generalizations are possible.

Great gray owls could be greatly affected by fire, depending on its severity. Stand-replacing fire may negatively affect the great gray owl due to the destruction of nesting sites such as vacated raptor nests [11,28,43,73,76,100,103] and dwarf mistletoe brooms [11,28,43,78,103,106]. Snag availability would probably increase, providing perching, roosting, and nesting sites [11,43,103,106]; however, great gray owls may not use these sites due to decreased canopy cover (see Preferred Habitat). Salvage logging could have negative effects. Mammalian prey species populations may be very low for the first several years following severe fire, but would eventually increase [13,18,28,38,99].

Low-severity wildfire and prescribed burns open dense forest structure and may benefit the great gray owl; however, the removal of large-diameter snags and dwarf mistletoe brooms used for nesting would be "detrimental" [81]. If prescribed surface burns are performed, some dead woody material on the forest floor needs to be retained due to its importance to the great gray owl [25,26,28,43,46] and mammalian prey species. To maintain prey species, prescribed burning should be restricted during the great gray owl's breeding season (see Timing of Major Life History Events) [46].

Great gray owls and spotted owls share similar habitat requirements, and may respond similarly to wildfire and prescribed fire. For detailed fire effects and use for the spotted owl, see spotted owl.

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