The great grey owl, also known as strix nebulosa, is a very large owl, documented as the world’s largest species of owl by length. They are found across North America and parts of Europe and Asia. Great grey owls are highly effective predators that hunt mostly small mammals such as voles, pocket gophers, and mice. Their huge size, sharp talons, and stealth hunting techniques make them formidable predators able to take down prey much larger than themselves.
Physical Description
Great grey owls stand out due to their incredibly large size, with impressive wingspans stretching nearly 5 feet across. They have a round facial disc that is nearly all feathers except for their bright yellow eyes. Their plumage is mottled grey and brown which provides excellent camouflage. Great grey owls have a large head that sits directly on the shoulders with no visible neck. The feathers around the face form a circular facial disc. The crown is flat with two ear tufts sprouting up that the owl can manipulate to express its mood. Their barred grey and brown plumage provides camouflage in the trees where they roost and hunt.
Great grey owls are sexually dimorphic in size, with females noticeably larger than males. Adult great grey owls range from 24-33 inches in length with a wingspan between 4.5-5 feet. Females are heavier, weighing 2.5-4.5 lbs while males are closer to 1.5-3 lbs. Their tails are relatively short for an owl.
Juvenile great grey owls have pale down feathers around their face and eyes and on parts of the body at first. As they mature, their adult plumage comes in over several months. By one year old, great grey owls resemble mature adults.
Range and Habitat
Great grey owls have an extensive range across northern parts of North America and Eurasia. In North America, their breeding range extends from Alaska across Canada and parts of the northern United States. They are found as far south as Oregon and Idaho in the west and Michigan and New York in the east. Small isolated populations exist in some mountainous regions of California, Arizona, Utah, Colorado, and New Mexico.
In Eurasia, great grey owls occupy a wide swath across Russia and Scandinavia. Their range extends as far west as Poland, Germany, and France and east towards Mongolia and northeastern China.
During winter, great grey owls will wander somewhat south of their breeding range in search of food. But they are restricted by their reliance on dense, old-growth forest habitat.
Great grey owls inhabit mature boreal forests across their range. They require areas of old-growth coniferous or mixed forest with openings and meadows nearby for hunting. Some key features of great grey owl habitat include:
- Abundant old trees for nesting and roosting
- Openings in the forest, such as meadows or bogs
- Low cover for hunting, such as short shrubs and grasses
- High populations of prey like voles and pocket gophers
During winter, great greys may venture into more open habitats near their forest home ranges in search of food.
Diet and Hunting
Great grey owls are effective predators that mostly hunt small rodents, especially voles. They also prey on other small mammals such as shrews, pocket gophers, deer mice, and kangaroo rats. Occasionally they will grab a bird such as a grouse or ptarmigan. Compared to most other owls, great greys have relatively small feet due to their high reliance on voles.
When hunting, great grey owls fly slowly over openings scanning for prey with their incredibly sharp vision and keen hearing. Once prey is spotted, they swiftly dive down talons-first to grab the animal in their strong grip. Great grey owls are able to plunge through snow to capture subnivean rodents.
They typically swallow prey whole and digest all but the fur and bones. Indigestible fur and bones are compacted into a pellet that the owl later regurgitates.
Great grey owls are crepuscular or active around dawn and dusk, though they may hunt at night when food is scarce. Their huge facial discs help channel faint sounds towards their ears to detect movements of even subnivean prey.
Optimal Foraging Strategy
Great grey owls have developed specialized hunting behaviors and preferences that amount to an optimal foraging strategy for the abundance and vulnerabilities of their typical prey items in northern forests.
Some key aspects of their strategy include:
- Focus on meadow voles – Abundant and easily caught prey
- Sit-and-wait hunting – Energy efficient technique suited for grabbing unsuspecting voles
- Low flight patrolling – Scans wide areas for prey while expending minimal energy
- Crepuscular schedule – Targets prey during their peak activity periods
- Elusive roosts – Dense tree cover protects from predators and weather while providing views over hunting grounds
This optimized hunting approach allows great grey owls to thrive on small prey across their northern forest environments.
Breeding and Nesting
Great grey owls nest in the broken top or cavity of a large tree, often a poplar or aspen. They do not build their own nests. In optimal habitat, nest sites are reused for decades by successive generations. The female scrapes a shallow depression in accumulated debris inside the cavity and lays 1-5 eggs (average of 2-3) in late March to April.
Only the female incubates the eggs while the male provides all her food. After a 28-33 day incubation, the eggs hatch over 2-3 days in May. Nestlings are covered in white down. They grow quickly on a diet of chopped up prey delivered by both parents. Young owlets are able to walk, wing flap, and tear food by 2-3 weeks old but do not leave the nest until near fledging.
The owlets fledge the nest at around 5-6 weeks old but are still unable to fly well. They scramble up branches flapping their wings while the parents continue to feed and defend them. After another couple weeks of climbing, fluttering, and short flights, the juveniles are capable of sustained flight and independence. They disperse from the parents’ territory a few months later as winter approaches.
Threats and Conservation
Great grey owl populations currently appear generally stable and they remain widespread across northern latitudes. But they face some conservation threats to monitor:
- Habitat loss – Due to logging, development, and wildfires
- Climate change – Could affect boreal forest ecosystems
- Rodenticide poisoning – From consuming poisoned prey
- Vehicle collisions – More common near roads
Key conservation actions to support great grey owl populations include:
- Protecting remaining old growth forest
- Allowing wildfires to burn naturally in some areas
- Limiting rodenticide use in their home ranges
- Enforcing reduced speed limits where owls are present
Responsible forest management and replicating natural disturbances like fire are important for maintaining the mature forest habitat preferred by great grey owls.
Interesting Facts
Here are some additional fascinating details about the great grey owl:
- One of the world’s largest owl species by length – often over 2 feet tall
- Weighs twice as much as the more common barred owl
- Has incredible hearing able to locate rodents under 20 inches of snow
- Almost entirely dependent on voles as prey – eats up to 1,600 per year!
- Wide facial disk acts like a satellite dish to locate sounds
- Feathers extend all the way to its talons, unlike most owls
- Prey are often swallowed whole and head-first
- Loses ability to digest food at temperatures over 86°F
- Essentially flightless while molting wing and tail feathers
- Juveniles have blue-grey eyes that turn yellow as adults
Conclusion
The great grey owl is an iconic and fascinating raptor of the northern forests. As the world’s largest owl by length, it cuts an imposing figure. Its cryptic plumage, stealth hunting tactics, and incredible hearing make it a supremely effective predator. Great grey owls play an important role helping regulate prey populations in their boreal forest ecosystem. With responsible management of old growth habitat and protection from poisons, these majestic giants can continue thriving for centuries to come.