Montana Field Guide

Great Gray Owl - Strix nebulosa

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).

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.

Montana Range

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 (2003) has transient Great Gray Owl records in very 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.

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, 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.

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.

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 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).

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.

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).