The great grey owl is a fascinating bird of prey that lives in the northern forests of North America and Eurasia. It is the largest owl species by length, though not by weight. The great grey owl has many special adaptations that allow it to survive and thrive in the harsh northern climate.
Physical Features
The great grey owl has striking physical features that set it apart from other owls. With a length of 24-33 inches, a wingspan of 54-60 inches, and a weight of 1.4-4.2 pounds, it is one of the largest owl species in the world. Its most distinctive feature is its large, round head that lacks ear tufts. The great grey owl has a round facial disc outlined in small, fine feathers. Its yellow eyes are framed by concentric gray rings. The plumage is soft and smooth with intricate patterns of concentric bars and spots. The base color is mottled gray to brown on the upperparts and barred gray and white on the underparts. The face is pale with bold black outline. Females are slightly larger than males.
Camouflage
The mottled plumage provides excellent camouflage in the mature mixed forests where great grey owls nest and roost. When perched motionless during the day, they blend seamlessly into the colors and patterns of tree bark and lichens. Their disruptive plumage allows them to remain undetected by both prey and predators.
Specialized Feathers
Great grey owls have several unique feather adaptations. Their wings are large relative to their body size allowing for silent flight. The leading edges of their wings and tail are finely fringed which softens turbulence as they fly. Their feathers lack stiffness and are exceptionally soft and fluffy compared to other owls. The soft feathering insulates them against the extreme cold of northern winters.
Facial Disc
Like other owls, great greys have a specialized facial disc of small, finely-textured feathers. The concave shape of the disc funnels sound to their ears which are located inside the disc. The facial disc acts like a radar dish allowing great greys to locate prey in complete darkness. Their hearing is highly refined and allows them to hunt at anytime, day or night.
Asymmetrical Ears
Owls have an amazing ability to precisely localize sounds in multiple dimensions. This is partly due to their asymmetrical ear placement within the facial disc. One ear is higher than the other. Sound reaches the elevated ear slightly sooner, allowing the owl to pinpoint if the sound is above or below them. The offset placement also helps them determine if the sound is in front or behind them.
Forward-facing Eyes
Like most birds of prey, the great grey owl has large, forward-facing eyes. Their eyes are specially adapted for excellent daytime vision. A bony ring strongly reinforces the eye socket allowing them to exert great force with their bite. Their eyes are immobile within the socket forcing them to turn their head to see in other directions. They are able to rotate their heads 270 degrees in each direction.
Sharp Talons
Great grey owls have large, sharp, and powerful talons used for killing prey. The needle-sharp talons and curved claws provide a strong grip to lift and carry prey as large as adult hares. The upper part of the foot is covered in small bumps called papillae. These papillae help them get a better grip when grasping struggling prey. The toes and talons are feathered which protects them from the extreme cold.
Hooked Beak
They have a large hooked upper beak used for tearing flesh from prey. The cutting edges of the beak are serrated which helps them neatly slice meat. The sharp lower beak is used for removing feathers and fur from prey. Together the upper and lower mandibles provide a forceful bite. The beak curves down towards the tip which gives it a distinctive hooked shape.
Range and Habitat
The great grey owl occupies the boreal forest regions of northern North America and northern Eurasia. In North America, their range extends from Alaska across Canada into the northern United States including Montana, Minnesota, Wisconsin, and northern Michigan. They are found throughout Russia and Scandinavia. Their breeding habitat is in mature coniferous or mixed forests near open meadows and wetlands.
Boreal Forests
The great grey owl is specially adapted to the cold, harsh conditions of the boreal forest. Their range coincides closely with the southern edge of the taiga forest belt that encircles the northern latitudes of the globe. They rely on mature forests with adequate openings for foraging.
Nesting Habitat
Great grey owls nest in broken top snags of larger trees that provide protection from predators and unfavorable weather. Nest trees are often 21-49 feet tall surrounded by small forest openings. They show high fidelity for previous nest sites if they successfully reproduce there. Nest reuse helps maintain territorial boundaries between breeding pairs.
Roosting Habitat
During the day, great greys roost on the branches of dense conifer trees that provide cover. Thick evergreen boughs shelter them from precipitation and conceal them from view. Maples, poplars, and aspens are also used on occasion. Roost sites average 16-33 feet high and are chosen based on cover density rather than tree species.
Foraging Habitat
Great grey owls forage in forest openings including meadows, bogs, marsh edges, agricultural fields, and forest clearings. These openings provide habitat for the small mammal prey upon which they depend. They will readily leave the security of the forest to hunt in more open areas.
Diet
Great grey owls are highly specialized predators that feed primarily on small mammals. Their menu consists mainly of voles and other rodents. They hunt by perching in wait and listening for prey with their keen sense of hearing.
Small Mammals
The great grey owl depends heavily on small mammal prey, especially voles. Voles makeup over 90% of prey items at some nests. Other small rodents frequently eaten include deer mice, red-backed voles, northern bog lemmings, woodland jumping mice, southern red-backed voles, and meadow voles. Non-rodent prey includes shrews, bats, and weasels.
Large Prey
Though uncommon, great greys will occasionally take larger mammals including snowshoe hares, squirrels, rats, and moles. Cases of them killing ducks, grouse, small hawks, and songbirds have also been documented. However, avian prey is not a normal part of their diet.
Hunting Habits
Great grey owls are sit-and-wait predators rather than active hunters. They perch on an elevated exposed perch watching and listening for prey. Once prey is pinpointed, they glide down quickly and snatch it with their talons. They carry prey back to their plucking post, often the top of a broken tree.
Food Caching
Great greys often cache extra food when prey is abundant. Cached prey provides emergency reserves when fresh food is limited. Cached food is wedged into tree cavities, tangled in branches, or impaled on twigs. Great horned owls and martens are known to steal cached food from this species.
Breeding and Nesting
Great grey owls nest in the late winter months. They are monogamous and generally mate for life barring the death of one partner. Courtship activities begin in late winter before nest construction.
Courtship
Male great greys initiate courtship in late winter by repeatedly bobbing while making low hooting sounds. If receptive, the female returns the hooting call. Pairs engage in synchronized duet hooting to cement the pair bond. Courtship feeding helps win over an unresponsive female.
Nest Sites
Great grey owls nest in broken-topped snags near forest openings. Cavities and old raptor nests are also used on occasion. Nest heights range from 6 to 70 feet off the ground. Nest trees average 25 inches in diameter. Aspen, poplar, spruce, and pine trees host most nest sites.
Egg Laying
The female lays 1-5 eggs at 1 to 2 day intervals in March or April. Average clutch size is 3 eggs. The eggs are smooth, glossy white and almost perfectly round. Egg dimensions average 1.8 x 1.6 inches and the incubation period is around 30 days.
Nestlings
Females perform most incubation and all brooding duties. The male provides all food until the nestlings are 2-3 weeks old. Nestlings are covered in dense white down. Their eyes open at around 4 days old. They fledge from the nest at 4-5 weeks old but remain dependent on their parents into summer.
Population Threats
Though great grey owl numbers are currently stable, there are several factors that could potentially impact populations in the future.
Habitat Loss
As with many boreal forest species, habitat loss poses risks for great grey owls. Logging that removes critical nesting or foraging habitat could reduce reproductive success. However, sustainable forestry that maintains suitable habitat may be compatible.
Prey Declines
Great grey owls could suffer if vole populations decline, as their diet depends heavily on this one prey group. Vole cycles naturally fluctuate but climate change may alter cycles long-term. Pesticide use also reduces vole numbers in agricultural areas.
Climate Change
Climate change models predict the boreal forest zone will shift northwards significantly in the coming decades. Great greys may lose breeding range if boreal habitat declines. Milder winters may also negatively impact vole populations.
West Nile Virus
West Nile virus has killed thousands of owls in North America over the past two decades. Great greys seem somewhat resilient but this disease still poses a concern. Mosquito control programs may help reduce transmission risks.
Conservation Status
Currently, great grey owl populations are broadly stable and they are classified as a species of Least Concern by the International Union for Conservation of Nature (IUCN). However, they are listed as Endangered or Threatened at the state level across much of their southern range in the United States. Monitoring will be important to ensure populations remain robust long-term.
Global Population
Globally, the great grey owl has an extremely large range and population. Though no precise data exist, the global population is believed to number over one million mature individuals. Numbers fluctuate locally but are steady range-wide.
United States
In the United States, great grey owls are listed as Endangered in Minnesota, Threatened in Wisconsin, and a Species of Special Concern in Michigan. Habitat loss caused declines across the southern parts of its range. Careful habitat management will be vital for maintaining US populations.
Eurasia
In Europe and Russia, great grey owl populations are relatively secure. They are not of significant conservation concern in Finland, Sweden, Norway or Russia. As a boreal forest specialist, maintaining habitat will allow them to persist in northern Eurasia.
Research and Conservation
Various research and conservation initiatives help improve our understanding and protect great grey owl populations.
Reintroduction Program
A successful reintroduction program in the 1980s helped restore great grey owls to some parts of the western United States where they had been extirpated. Wild owls from Canada were relocated to suitable protected habitat in Oregon and California.
Migration Research
Banding and telemetry studies revealed that some great grey owls in the western US and Canada migrate south in winter while other populations are year-round residents. Migrants travel up to 1,000 miles between breeding and wintering grounds.
Genetic Research
Analysis of genetic markers shows great grey owls have high genetic diversity across their range. Three distinct sub-populations exist: West Coast US/Canada, East Coast US/Canada, and Eurasia. These groups show evolutionary differentiation.
Feather Mercury Studies
Feather samples show great grey owls accumulate mercury from environmental sources, but not at levels that impact reproduction. Their diet of small mammals exposes them to mercury. Monitoring will reveal if levels become problematically high.
Habitat Protection
Acquiring forest reserves with suitable nesting habitat and foraging openings is key for protecting great grey owls. Conservation easements also prevent development on private lands. Careful forest management maintains habitat quality on public lands.
Fun Facts
Beyond the great grey owl’s ecological role, some aspects of their biology and behavior are quite fascinating.
Unusual Nest Sites
Though tree cavities are most common, great greys have nested in some bizarre sites. These include oldsquirrel dreys, atop stumps, in hollow logs, in cliff crevices, and even in an abandoned boat.
Impressive Hearing
From 50 yards away, a great grey owl can detect a mouse running under a foot of snow. Their hearing is up to 10 times better than a human’s. They can even hear prey tunnels collapsing beneath the snow’s surface.
Daytime Hunting
While most owls are nocturnal, great greys routinely hunt during daylight. Their specialized eyes and ears allow them to effectively forage whenever small mammals are active, both day and night.
Morning “Duets”
Breeding pairs vocalize together at dawn and dusk in a territorial display. The male hoots repeatedly while the female calls occasionally between his hoots. This synchronized duetting advertises the pair’s nest site.
Unusual Molt
Great grey owls molt most of their flight feathers early in the breeding season rather than later like most bird species. This early molt may ensure they have peak flying ability during chick rearing.
Summary
The great grey owl survives the harsh conditions of the northern forests through specialized adaptations like its soft insulating plumage, accurate auditory hunting system, and hooked beak and talons for securing prey. Its large size and disruptive coloration help this sit-and-wait predator remain hidden. While currently stable, great grey owl populations face potential threats from habitat loss and climate change. Increased awareness and habitat protections will help ensure the survival of this unique northern hunter.