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Great Gray Owl - Strix nebulosa
Species of Concern Native Species Global Rank :
G5
State Rank :
S3S4
(see State Rank Reason below)
Agency Status USFWS :
MBTA
USFS :
BLM :
SENSITIVE
FWP SWAP :
SGCN3, SGIN
PIF :
3
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Copyright by: The Macaulay Library at the Cornell Lab of Ornithology, Ithaca, NY, all rights reserved.
State Rank Reason (see State Rank above)
Species is uncommon across much of western Montana. It faces moderate threats from timber harvest and fire. Initial surveys have established baseline occupancy estimates, but trend is still poorly characterized.
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).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see
Marks et al. 2016, Birds of Montana. 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.
Species Range
Montana Range
Range Descriptions
Year-round
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations: 1289
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
Relative Density
Recency
SUMMER (Feb 16 - Dec 14)
Direct Evidence of Breeding
Indirect Evidence of Breeding
No Evidence of Breeding
WINTER (Dec 15 - Feb 15)
Regularly Observed
Not Regularly Observed
(Observations spanning multiple months or years 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.
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 (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
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 2012, Adams 2003, and Werner et al. 2004);
Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
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 listed as associated with 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 listed as 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.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific 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 assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
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:
mtnhp.org/requests ) 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. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
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.
Commonly Associated with these Ecological SystemsForest and Woodland Systems
Grassland Systems
Recently Disturbed or Modified
Wetland and Riparian Systems
Occasionally Associated with these Ecological SystemsForest and Woodland Systems
Recently Disturbed or Modified
Wetland and Riparian Systems
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).
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).
Stewardship Responsibility
References
Literature Cited AboveLegend:
Additional ReferencesLegend: Do you know of a citation we're missing? 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 databaseEffects of recreation on Rocky Mountain wildlife: a review for Montana . [Montana]: Montana Chapter of the Wildlife Society.
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