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Great Gray Owl - Strix nebulosa

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Species of Concern

Global Rank: G5
State Rank: S3

Agency Status
USFWS:
USFS:
BLM: SENSITIVE
FWP Conservation Tier: 2
PIF: 3


 

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Copyright by: The Macaulay Library at the Cornell Lab of Ornithology, Ithaca, NY, all rights reserved.
 
General Description
Great Gray Owls are the largest owl species in North America. They have a wingspan over 4 feet with a body length of up to 27 inches. They can weigh over 2 pounds. Females are usually larger than males, but they are otherwise identical in appearance. Great Gray Owls have a large, rounded, half-domed head with a flat face and no ear tufts (Bull and Duncan 1993, Sibley 2000). Their eyes are yellow, but look rather small due to the ringed facial disks. The bill is mostly yellow with a black patch below separating white lores that give Great Gray Owls their classic bow-tied appearance. The plumage is mostly gray with patches of whites and browns. The tail is fairly long and is also brown and gray (Bull and Duncan 1993).

The vocalization of Great Gray Owls is a series of deep resonating "whoos" that falls in pitch and accelerates (Cramp 1985).

Diagnostic Characteristics
Great Gray Owls are distinguished from Barred Owls (Strix varia) by their much larger size, yellow eyes, bow-tie under the face, the lack of barring on the breast, and the better defined concentric rings on the face (Bull and Duncan 1993). Great Gray Owls are distinguished from their other closest relative, the Spotted Owl (Strix occidentalis), by many of the same physical characteristics, much larger size, yellow eyes, and bow-tie. Also, the ranges of Great Gray Owl and Spotted Owl do not usually overlap, unless extreme southern movements occur by Great Gray Owls in winter.

General Distribution
Montana Range



Western Hemisphere Range

 


Summary of Observations Submitted for Montana
Number of Observations: 477

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

Breeding
(direct evidence "B")


Breeding
(indirect evidence "b")


No evidence of Breeding
(transient "t")


Overwintering
(regular observations "W")


Overwintering
(at least one obs. "w")



 

(Records associated with a range of dates are excluded from time charts)



Migration
Very little information regarding migratory patterns exist for Great Gray Owls in the state, as they are a resident species in Montana, both during the breeding season and in winter. The Montana Bird Distribution Committee (2012) has transient Great Gray Owl records for every month of the year. During periods of low prey abundance and/or large snowfalls birds may move from higher to lower altitudes within the state. Also, birds from Canada may move into the state during winter for similar reasons.

Habitat
Little specific habitat information for Montana is currently available, as systematic surveys for Great Gray Owls have not been done. Great Gray Owls are known to use lodgepole pine/Douglas-fir in Montana. Habitat information from other Great Gray Owl sources state that their habitat is dense coniferous and hardwood forest, especially pine, spruce, paper birch, poplar, and second-growth, and especially near water. They forage in wet meadows, boreal forests and spruce-tamarack bogs in the far north, and coniferous forest and meadows in mountainous areas.

Great Gray Owls nest in the tops of large broken-off tree trunks (especially in the south), in old nests of other large birds (e.g., hawk nest) (especially in the north), or in debris platforms from dwarf mistletoe, frequently near bogs or clearings. Nests are frequently reused (Franklin 1988) and the same pair often nests in the same area in successive years.

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (high, medium, or low) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2001, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of “observations versus availability of habitat”.
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were associated as using an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at bmaxell@mt.gov or (406) 444-3655.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species’ known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana’s amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
No food habit information is available for Great Gray Owls in Montana. However, information from other areas in the species' range indicates small mammals, especially rodents (i.e. voles), dominate prey over most of the range. Pocket gophers also dominate the diet of Great Gray Owls in North America. They usually forage in open areas where scattered trees or forest margins provide suitable sites for visual searching. They also use sound to locate prey under snow cover.

Ecology
Ecological information for Great Gray Owls in Montana is not available. Information from other areas of the species' range, including Oregon and Canada, indicate that Great Gray Owls loosely congregate, probably in response to abundant prey; groups of up to 15 individuals have been observed in late winter (Hayward and Verner 1994). Some Great Gray Owls may remain on the breeding territory all year. Others move irregularly in search of favorable foraging conditions. The average home range size for breeding adults in Oregon was 4.5 square kilometers and in Wyoming, 2.6 square kilometers. The maximum distance traveled from the nest averages 13.4 kilometers (Hayward and Verner 1994). The maximum distance that juveniles dispersed in their first year ranged from 7.5 to 32 kilometers in Oregon. Adults moved 3 to 43 kilometers during the same period (Johnsgard 1988). Adults and juveniles travel much greater distances in the northern parts of their range, some up to 753 kilometers in Canada (Hayward and Verner 1994). Predation by Great Horned Owls (Bubo virginianus) was the greatest known mortality factor in northern Minnesota and southeastern Manitoba (Duncan 1987).

Reproductive Characteristics
Little information exists regarding Great Gray Owl reproduction in Montana. Systematic surveys have yet to be done in the state. However, information from other areas where Great Gray Owls occur indicates nesting begins in March or April on broken-topped snags or old stick nests of other birds. The average egg dates are late March to May in Alberta, late April to early June in Ontario, and peak mid-April to late May in California. The mean date for the first egg is May 5 in southern Idaho and northwestern Wyoming. Egg-laying may be delayed in years with deep snow (Franklin 1988). Clutch size is 2 to 5 (usually 2 to 3 or 3 to 4). Incubation lasts 28 to 29 days and is completed by the female (male brings food). Young begin to leave the nest at 3 to 4 weeks (4 weeks in Idaho/Wyoming), fly well at 5 to 6 weeks (6 weeks in Idaho/Wyoming), and are independent at about 4 to 5 months (Idaho/Wyoming) (Franklin 1988).

Great Gray Owls usually breed for the first time at 3 to 4 years of age. The pair bond is not maintained outside of the breeding season, but the bond may reform if both birds return to the same breeding territory. Some pairs may not breed in years of low prey abundance.

Management
No known active management is ongoing for Great Gray Owls in the state. However, habitat management must take into account a long-term view of forest succession and consider landscape and regional forest patterns. Because of the owl's large home range, management must be coordinated among administrative units to maintain links between interacting biological units (Hayward and Verner 1994).


References
  • Literature Cited AboveLegend:   View WorldCat Record   View Online Publication
    • Bull, E. L. and J. R. Duncan. 1993. Great gray owl (Strix nebulosa). In: A. Poole and F. Gill, eds. The Birds of North America, Number 41. The Academy of Natural Sciences, Philadelphia and The American Ornithologists' Union, Washington, DC. 16 pp.
    • Cramp, S., ed. 1985. Handbook of the birds of Europe, the Middle East, and North Africa. Volume 4, the birds of the western Palearctic. Terns to woodpeckers. Oxford University Press, Oxford, England.
    • Duncan, J. R. 1987. Movement strategies, mortality, and behavior of radio-marked great gray owls. In: Nero, R.W., R. J. Clark, R. J. Knapton, and H. Hamre, eds. Biology and conservation of northern forest owls. pp. 101-107. USDA Forest Service General Technical Report RM-142. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.
    • Franklin, A. B. 1988. Breeding biology of the great gray owl in southeastern Idaho and northwestern Wyoming. Condor 90:689-696.
    • Hayward, G.D. and J. Verner. 1994. Flammulated, boreal, and great gray owls in the United States: A technical conservation assessment. Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado. USDA Forest Service General Technical Report RM-253.
    • Johnsgard, P. 1988. North American owls: biology and natural history. Smithsonian Institution Press. 336 pp.
    • Montana Bird Distribution Committee. 2012. P.D. Skaar's Montana bird distribution. 7th Edition. Montana Audubon, Helena, Montana. 208 pp. + foldout map.
    • Sibley, D. A. 2000. The Sibley guide to birds. National Audubon Society and Alfred A. Knopf, Inc., New York, NY. 544 p.
  • Additional ReferencesLegend:   View WorldCat Record   View Online Publication
    Do you know of a citation we're missing?
    • American Ornithologists' Union. 1998. Check-list of North American birds. 7th edition. American Ornithologists' Union, Washington, D.C. 829 pp.
    • BRUNTON, D. F., AND R. PITTAWAY, JR., OCT.-DEC. 1971, OBSERVATIONS OF THE GREAT GRAY OWL
    • Bull, Evelyn L., and James R. Duncan. 1993. Great Gray Owl (Strix nebulosa). Species Account Number 041. The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology; Retrieved 3/25/2008 from The Birds of North America Online database
    • California Department of Fish and Game (CDF&G). 1990. 1989 annual report on the status of California's state listed threatened and endangered plants and animals. 188 pp.
    • Casey, D. 2000. Partners in Flight Draft Bird Conservation Plan Montana. Version 1.0. 287 pp.
    • Duncan, J.R. 1997. Great Gray Owls (Strix nebulosa nebulosa) and forest management in North America: a review and recommendations. J. Raptor Res. 31(2):160-166.
    • Ehrlich, P., D. Dobkin, and D. Wheye. 1988. The birder’s handbook: a field guide to the natural history of North American birds. Simon and Schuster Inc. New York. 785 pp.
    • Holt, D.W., and J.M. Hillis. 1987. Current status and habitat associations of forest owls in western Montana. Pages 281-288 in: Biology and conservation of northern forest owls: symposium proceedings, Feb. 3-7, Winnepeg, Manitoba. Gen. Tech. Rep. RM-142. Fort Collins, CO. USDA, Forest Service.
    • Johnsgard, P. A. 1992. Birds of the Rocky Mountains with particular reference to national parks in the northern Rocky Mountain region. Lincoln: University of Nebraska Press. xi + 504 pp.
    • Lenard, S., J. Carlson, J. Ellis, C. Jones, and C. Tilly. 2003. P. D. Skaar's Montana Bird Distribution, 6th Edition. Montana Audubon: Helena, MT, 144 pp.
    • Montana Bird Distribution Online Database. 2001. Helena, Montana, USA. April-September 2003.
    • National Forest Service. 1990. Memo to Montana Natural Heritage Program. Kings Hill Ranger District, White Sulpher Springs, MT.
    • Stearns-Roger Inc., 1975, Environmental baseline information of the Mount Vernon Region, Montana. January 31, 1975.
    • Thompson, Richard W., Western Resource Dev. Corp., Boulder, CO., 1996, Wildlife baseline report for the Montana [Montanore] Project, Lincoln and Sanders counties, Montana. In Application for a Hard Rock Operating Permit and Proposed Plan of Operation, Montanore Project, Lincoln and Sanders Counties, Montana. Vol. 5. Stroiazzo, John. Noranda Minerals Corp., Libby, MT. Revised September 1996.
    • TVX Mineral Hill Mine, Amerikanuak, Inc., Gardiner, MT., 2002, Yearly summary of wildlife observation reports. 1990-2002 Letter reports.
    • U.S. Forest Service. 1991. Forest and rangeland birds of the United States: Natural history and habitat use. U.S. Department of Agriculture, Forest Service Agricultural Handbook 688. 625 pages.
    • Verner, J. 1994. Current management situation: Great Gray Owls. Pp. 155-158in G.D. Hayward and J. Verner, tech. eds. Flammulated, Boreal, and Great Gray Owls in the United States: A technical conservation assessment. Gen. Tech. Rep. RM-253. U.S.D.A. Forest Service, Rocky Mountain Forest and Range Experiment Station. Fort Collins, CO. 214 pp. 3 maps.
    • Westmoreland Resources, Inc., Hardin, MT., 1981, Upper Sarpy Basin Wildlife Study. In 1981 Wildlife Report. April 1982.
  • Web Search Engines for Articles on "Great Gray Owl"
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Citation for data on this website:
Great Gray Owl — Strix nebulosa.  Montana Field Guide.  Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.  Retrieved on September 1, 2014, from http://FieldGuide.mt.gov/detail_ABNSB12040.aspx
 
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