Great Gray Owl Biology

A Reference for North and Central American Owls

Name: Great Gray Owl – Strix nebulosa
Other Common Names: Dark Wood-Owl; Lapland Owl; Striped Owl; Sooty Owl; Spectral Owl.

Subspecies: There is only one race of Great Gray Owl in North America although there is a widespread northern Eurasian race.
S. n. nebulosa is the North American race of Great Gray Owl. Its approximate breeding range is shown on the range map. Winters in the breeding range but will also wander south. *See Movements.

Measurements and Weights:
Wingspan: 54 – 60 in.
Length: 24 – 33 in.
Tail: 11 3/4 – 13 3/4 in.
Average Weight: Male: 34 oz.
Average Weight: Female: 46 oz.

Description: This is the largest Owl in North America although it is not the most massive. Males and females are identical in plumage except that the females may appear slightly darker. Distinctively large facial disk of light gray with darker gray or brown concentric rings. Facial disk has a thin dark brown border that becomes white along the bottom edge. Has a black chin with white along the sides that run into the bottom white border of the facial disk (sometimes referred to as a “white mustache and black bow tie”). Conspicuous white eyebrows and lores. The Great Gray has a large round head and lacks ear tufts. The general colors of the upper parts are grayish-brown to sooty brown broken by transverse mottling of grayish-white and dark with scattered short dark streaks. The owl becomes more brown with age. The bottom portion of the wings (primaries and secondaries) and the tail are barred with dark and light gray. The under parts are a grayish-white with dark grayish-brown streaks. The iris of the eyes are lemon yellow and the bill is bright yellow to pale olive green.

Young: Initially the young have a grayish down above and white down below. The juveniles are olive-brown with dark bars and white spots above. Light gray- white below with dark bars; bold black facial marks. Adult plumage develops over the first 5 months but first year birds have white tipped flight feathers.

Habitat:

The Great Gray Owl inhabits many types of forests in North America. It favors dense coniferous forests with close proximity to muskegs, meadows or open fields. This combination allows conifer nesting and roosting along with the abundance of small rodents that occur in forest openings. In the Sierra Nevadas of California the Great Gray is a summer resident from 4000 -7000 ft. in elevation and winter resident from 3000 – 5000 ft. Nesting and summer records seem to concentrate in the 6000 – 7000 ft. meadows although there are nesting records as low as 2800 ft. and as high as 11,000 ft. They breed in mixed-conifer forests from 3000 – 6000 ft. and red fir from 6000 – 9000 ft. in elevation. The owls are prone to moving into the higher lodgepole pines in the late summer. In the winter the records seem to concentrate around the 4000 ft. level. Other records including the Palearctic habitat ranges are from sea level to 3200 ft. Other breeding habitats include tamarack forests (Manitoba), tamarack-black spruce, forested wetlands (Saskatchewan), black ash / basswood (Minnesota), and balsam poplars / white spruce (Alaska).

Food and Feeding:

The Great Gray Owl’s diet consists of almost entirely small rodents. About 90% of their diet consists of pocket gophers and voles. Other small mammals taken by the owl include mice, squirrels, young rabbits, hares, rats, moles, and weasels. Also taken are birds, usually small, although there are records of Sharp-shinned Hawks, ducks, and grouse. Small mammals are usually swallowed whole while larger prey is torn into pieces. The Great Gray can also detect prey under the snow by sound alone and will dive into the snow for hidden prey. Generally they hunt from a perch by listening and watching. Primarily a nocturnal and crepuscular owl but may occasionally hunt by day on dark overcast days during the winter months, and while feeding young.

Breeding:

The Great Gray does not build its own nest or modify it in any way other than to potentially deepen the cup. Most nesting is done in abandoned raptor or crow nests or broken off treetops. Typically clutch size is 3 – 5 eggs but 1 – 9 is possible. In the case of the loss of the eggs, re-nesting may occur two additional times but only one clutch is raised yearly. Nest sites may also be used for multiple years. The female usually lays 1 egg per day and the incubation period is generally 28 – 36 days. The male does all the hunting during this period. Although the owlets leave the nest at 20 – 29 days they are incapable of flight (but can climb trees well) for another 7 – 14 days. Fledging occurs before they are 55 days old but they remain cared for by the female until 4 – 5 months of age when they begin to disperse. Great Horned Owls are serious predators of the young although humans are responsible for the greatest losses of the eggs and chicks.

Movements and Life Span:

The Great Gray is sedentary with only minor or no movements between summer and winter in many areas. Each year a limited number of owls will move through dispersals and food scarcity into the Southern Canadian Provinces and the Northern U.S. It is also regular (each 3 – 5 years) for irruptions to occur where large movements into the Northern U.S. and East Coast occur related to harsh winter conditions and prey availability. The Great Gray is a long-lived owl. Banded birds have been recovered at 13 years of age and captive birds have lived to 27 years of age.

 

Conservation: The Great Gray Owl is not globally threatened although its population density is generally very low. There are tremendous variations in its population over extended periods of time related to prey availability. Deforestation, automobile collisions, development, pocket gopher poisoning, and cattle grazing are potential dangers.