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Strix nebulosagreat grey owl

By Rohit Tonk

Geographic Range

Strix nebulosa resides in Alaska, Canada, the higher elevations of the Rocky Mountain States, northern Minnesota and northern Wisconsin. Also, S. nebulosa breeds from northern Yukon to northern Manitoba and northern Ontario, south locally to central California, northern Idaho, northwestern Wyoming, central Saskatchewan, northern Minnesota, and south central Ontario. Winters generally through the breeding range, wandering south irregularly to the northern tier of States. It also occurs widely across Europe and Asia. (Osborne 2001, UNEP World Conservation Monitoring Center 2001).

Habitat

In North America, Strix nebulosa inhabits dense coniferous forests in Canada, and montane coniferous forests of the western States. It usually prefers pine and fir forests, rarely straying far out onto tundra barrens and muskeg marshes. Nests in mature poplar woodlands, well secluded from human activities, and in spruce stands with islands of tamarack. In winter, it may inhabit forests, sparse woodland edges bordering open fields, weedy fields with posts or scattered low trees or bushes, or brackish tidal meadows (Baetsen 2000; The Owl Pages).

Physical Description

The Great Gray Owl is the tallest owl in Alaska standing at a length 24-33 inches high, with a wing span of 54-60 inches, depending on degree of maturity. Strix nebulosa is larger and grayer than other owls and its round head does not have any ear tufts. Its bill and eyes yellow.

The owl has a distinctive facial disk, with two obvious gray concentric circles. The feathers of the disk help direct sounds toward the ear openings that are hidden by feathers. The owl also has an asymmetrical skull with large bony cups surrounding the ear openings.

In addition to the predominately gray plumage and distinctive facial disk, the bird has a black chin spot just above two white-feathered mustaches and it has a prominent white collar on the front of the neck. Ventrally, the owl is exhibits varying shades of dark and light grays, browns, and white. The dorsal side has a little less white than the ventral side. The tail is long and extends beyond the folded wings.

Adaptations for hunting include the facial disk, soft feathers so flight is silent, and the ability to turn its head three quarters of a circle (270 degrees).

(The Owl Pages; Compton's Encyclopedia 1998; MacBride Raptor Project 1997; Baetsen 2000; Wolf 2000).

  • Range mass
    790 to 1454 g
    27.84 to 51.24 oz

Reproduction

Breeding takes place in late winter with the pair generally utilizing an abandoned hawk or crow's nest. The female Strix nebulosa lays eggs in March- June, depending on temperature range (egg laying may be delayed in deep snow years). Two to five dull white oval eggs are laid and are incubated by the female Strix nebulosa for a period of 28-29 days. The owlets hatch covered by soft white down with their eyes open. Both parents feed the young by bringing food to the nest, tearing into very small pieces that are eagerly consumed by the little ones. Soon the down begins to disappear and is replaced by feathers. Once the owlets are 'feathered out' they begin the pre-flight exercises. They can be observed walking around the top of their nest flapping their wings and gripping the nest edge with their talons. Young leave nest after three to four weeks with the ability to climb well. (The Owl Pages).

  • Average eggs per season
    2
    AnAge
  • Average time to hatching
    30 days
    AnAge

Lifespan/Longevity

Behavior

Strix nebulosa is a very reclusive owl. The male prepares for breeding and the nesting season as spring approaches by performing aerial displays and bringing food to the female. Strix nebulosa may not breed, but when they do, the number of eggs laid is related to food abundance. The years with a surfeit of mice, the owls will tend to lay more eggs and more young survive the nestling stage. Strix nebulosa inhabit coniferous forests of the Northern Hemisphere; they tend not to migrate but will leave their territories if their food supply runs short. Strix nebulosa hunt equally well both day and night, as they have both excellent hearing and vision. The main predator of the Great Gray Owl is the great horned owl, although both of these birds are often harassed by ravens and other small birds. (Baetsen 2000; The Owl Pages; Huff et al. 1997; Osborne 2000; Compton's Encyclopedia 1998).

Communication and Perception

Food Habits

In the wild, Strix nebulosa feeds primarily on small rodents such as voles and pocket gophers. Small rodents composed 80-90% percent of the diet while other mammals (mainly shrews) and birds composed the remainder (The Owl Pages).

The Great Gray Owl hunts by perching on a tree overlooking a meadow or open area. The owl's keen hearing enables it to accurately determine the location of its prey, even under two feet of snow or in tunnels. Once the owl locates some food, it silently glides from its perch and plunges into the snow to grab the rodent with its sharp talons. Fresh "plunge marks" will occasionally show an imprint of the owl's outstretched wing feathers where the owl dropped into the snow. In many areas these marks are often the only indication that Great Gray Owls are in the area (MacBride Raptor Project, Wolf 2000, Baetsen 2000).

Economic Importance for Humans: Positive

Strix nebulosa is important in the ecological balance; they scavenge and dispose of carrion and provide a check on rodent populations. Also, this rare owl draws many bird-watchers from everywhere. In Alaska, Athabaskans may use it as a food source due to its stored winter fat.(Compton's Encyclopedia 1998; Osborne 2000).

Economic Importance for Humans: Negative

The restrictions enforced on the logging industry because of the threatened status, will most likely be costly, and will potentially set back any business that relies on these resources for lumber and wood products. (Mann)

Conservation Status

The U. S. Department of Interior Bureau of Land Management considers Strix nebulosa to be a sensitive species, and it is protected in the United States on both federal and state levels. It has been the subject of extensive management studies (Huff et al. 1997)

The Great Gray Owl is rarely seen by people and is very vulnerable to human disturbance such as clearing of forests for timber or farming. The main limit to its distribution is the availability of nest sites. If there are sufficient nest sites, then other factors such as food supply, determine how many owls live in the area. Chemicals used in exterminating mice and other pests have detrimentally affected the food chain of Strix nebulosa

Wildfires can increase the availability of nest sites by creating suitable stumps, and they can also increase mouse populations.

(Idaho Conservation Data Center 2001, Huff et. al 1997, Mann,

Osborne 2000).

Contributors

Rohit Tonk (author), West Windsor-Plainsboro High School, Joan Rasmussen (editor), West Windsor-Plainsboro High School.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

References

Baetsen, R. 2000. "Great Gray Owl (Strix nebulosa)" (On-line). Accessed 12 Aug. 2000 at http://www.northbirding.com/rbaetsen/greatgray.htm.

Comptons Encyclopedia, 1998. "BIRDS OF PREY" (On-line). Accessed 11 Aug. 2000 at http://www.comptons.com/encyclopedia/ARTICLES/0000/00229376_A.html#P21.

Huff, M., J. Henshaw, E. Laws. 1997. "Great Gray Owl survey status and evaluation of guidelines for the Northwest Forest Plan" (On-line). Accessed 12 Aug. 2000 at http://www.or.blm.gov/surveyandmanage/SP/Great%20Gray%20Owl/icover.htm.

Idaho Conservation Data Center, 2001. "Rare Birds" (On-line). Accessed 8 March 2001 at http://www2.state.id.us/fishgame/Info/CDC/bird.htm.

MacBride Raptor Project, 1997. "Great Gray Owl" (On-line). Accessed 6 Aug. 2000 at http://www.ai-design.com/stargig/raptor/global/content/report/GreatGrayOwl.html.

Mann, M. "THE GREAT GRAY OWL - BIRD BIOGRAPHIES" (On-line). Accessed 12 Aug. 2000 at http://www.sicamous.com/bluheron/Gowl_bio.html.

Osborne, T. 07/24/2000. "Great Gray Owl" (On-line). Accessed 5 Aug. 2000 at http://www.state.ak.us/local/akpages/FISH.GAME/notebook/bird/grayowl.htm.

The Owl Pages, "Great Gray Owls - Strix nebulosa" (On-line). Accessed 12 Aug. 2000 at http://owlpages.com/species/greatgrey/.

The Raptor Center, "RAPTOR FACTS" (On-line). Accessed 9 Aug. 2000 at http://www.raptor.cvm.umn.edu/raptor/rfacts/ggo.html.

UNEP World Conservation Monitoring Center, 2001. "Threatened and Endangered Species: Strix nebulosa" (On-line). Accessed 8 March 2001 at http://www.unep-wcmc.org/index.html?http://ims.wcmc.org.uk/isdb/Taxonomy/tax-species-result.cfm?Genus=Strix&Species=nebulosa~main.

Wolf, L. 16-May-2000. "Hunters of the Sky" (On-line). Accessed 12 Aug. 2000 at http://www.acnatsci.org/raptors/owl.html.

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