Great grey owls are one of the largest owl species in North America. They are highly skilled predators that hunt a variety of prey. In this article, we will explore the hunting and feeding habits of these fascinating birds.
The great grey owl (Strix nebulosa) is a very large owl, recognized by its impressive size, round head, and forward-facing yellow eyes surrounded by black rings. Adults have a wingspan of approximately 4 to 5 feet. Their mottled gray plumage with irregular white spots provides excellent camouflage against tree bark where they roost during the day.
Great grey owls inhabit the northern boreal forests of North America, throughout Canada and Alaska. They are divided into three subspecies: the Pacific great grey owl inhabits the west, the Northern great grey owl inhabits central Canada and the Rocky Mountains, and the Eastern great grey owl inhabits southeastern Canada and the northeastern United States.
As opportunistic predators, great grey owls hunt a wide variety of prey, depending on their habitat and abundance. Their preferred foods include small rodents such as voles, pocket gophers, deer mice, and lemmings. However, they will also prey on larger animals such as rabbits, weasels, ducks, and grouse when given the opportunity.
Hunting Habits
Great grey owls employ patient hunting techniques to ambush prey. Their light, fluffy feathers allow them to fly silently, helping them sneak up on prey undetected. While perched on an elevated roost, they scan the ground for movements indicating prey. Once detected, they swoop down with claws outstretched to snatch their target.
To help locate prey running beneath snow, great grey owls rely on their acute sense of hearing. They can pinpoint the faint sounds of rodents scurrying in tunnels underneath. Great greys have asymmetrical ear openings that funnel sound to their left ear, assisting them in precisely locating prey. This adaptation gives them an important advantage when hunting in deep snow.
Great greys are crepuscular hunters, most actively hunting at dusk and dawn. However, they will hunt opportunistically both day and night. During peak feeding periods such as nesting season, great greys may hunt for up to 12 hours per night. Their sharp talons and powerful grip allow them to snatch and carry prey as heavy as mature rabbits or ducks.
Diet and Feeding
The diet of great grey owls can be divided into the following categories:
Small Rodents
Small rodents such as voles, deer mice, pocket gophers, jumping mice, and lemmings make up the bulk of the great grey owl’s diet. They may eat over 1,600 rodents per year. Great grey owls can detect rodents moving deep beneath snow and leave shallow diving craters in the snow when catching prey.
Large Rodents
When available, great greys may also prey on larger rodents including muskrats, ground squirrels, rats, and mountain beavers. More powerful than small owl species, great greys can subdue and carry these heftier rodents.
Birds
Great horned owls opportunistically prey on various birds, including grouse, ptarmigan, jays, blackbirds, woodpeckers, doves, and smaller owl species. Both adult and juvenile birds may be taken.
Other Vertebrates
Less commonly, great grey owls take other vertebrate prey, including fish, lizards, frogs, snakes, bats, and young cottontail rabbits. Rabbits are a significant part of the great grey diet in winter when birds migrate out of their territories.
Invertebrates
While not a primary food source, great grey owls will occasionally eat invertebrates including crickets, grasshoppers, beetles, and caterpillars when vertebrate prey is scarce.
Prey Type | Examples |
---|---|
Small rodents | Voles, deer mice, pocket gophers, lemmings |
Large rodents | Muskrats, ground squirrels, rats, mountain beavers |
Birds | Grouse, ptarmigan, woodpeckers, jays |
Other vertebrates | Rabbits, fish, lizards, frogs, snakes, bats |
Invertebrates | Crickets, grasshoppers, beetles, caterpillars |
Great grey owls are voracious predators, capable of consuming 1-5 prey animals per day. This amounts to a whopping 600-3,000 small rodents consumed each year. They have even been known to cache excess food when prey is abundant.
Hunting Adaptations
Great grey owls possess several key adaptations suited for hunting in northern forests and snowy conditions:
- Dense feathering – Provides insulation in frigid environments
- Thick plumage – Muffles flight noises while hunting
- Facial discs – Funnels sound to ears to precisely locate prey
- Asymmetrical ear openings – Improves directional hearing
- Sharp talons – For grasping and carrying prey
- Powerful grip – Holds large prey like rabbits and ducks
- Acute vision – Spot prey in low light conditions
- Camouflage – Blends into tree bark where they roost
In addition, great grey owls nest early to coincide with seasonal peaks in prey. They also may migrate locally to track rodent and rabbit populations.
Hunting Behavior
When hunting, great grey owls utilize the following behaviors and strategies:
- Patient perching – Scans ground from elevated perch for long periods while remaining perfectly still.
- Sound localization – Precisely pinpoints prey location by orienting to faint rustling sounds.
- Short-distance flights – Flies brief distances between perches while hunting to maximize coverage.
- Cursorial hunting – Runs along the ground pursuing prey once detected.
- Snow plunging – Plunges feet-first into snow to grab hidden rodents underneath.
- Crepuscular activity – Most active hunting at dawn and dusk when prey is also active.
- Opportunistic hunting – Hunts diurnally and nocturnally depending on prey availability.
Great grey owls often hunt from a regular series of perches within their home territory. They frequently reuse lookout posts that provide an optimal view of potential rodent trails and burrows.
Prey Handling and Consumption
Once prey is captured, great grey owls employ a series of behaviors to handle and consume the animal:
- Powerful talon grip – Uses sharp talons and crushing grip to subdue large struggling prey.
- Biting – Uses strong beak to deliver disabling or lethal bites to prey’s neck.
- Carrying – Grips prey in talons and flies back to nest or feeding perch.
- Plucking – Removes fur, feathers, scales, or skin with beak before eating prey.
- Tearing – Uses beak and talons to tear prey into pieces for swallowing.
- Swallowing – Swallows prey slowly, usually head or front quarters first.
- Pellet regurgitation – Regurgitates indigestible fur, feathers, and bones as oval pellets.
Great grey owls swallow prey whole whenever possible. After digestion, they regurgitate compact oblong pellets containing compressed indigestible materials from the prey. Analysis of regurgitated pellets provides insight into great grey owl diets.
Impacts of Prey Declines
Great grey owl populations are highly dependent on adequate prey populations. When cyclic prey species like voles and lemmings undergo population declines, it can have significant impacts on great grey owls:
- Lower reproductive success – Produce fewer eggs and offspring.
- Difficulty provisioning young – Higher chick mortality rates.
- Poor physical condition – Loss of body mass, poor feather condition.
- Forced migration – May irrupt outside normal ranges in search of food.
- Increased starvation risk – Particularly for juveniles.
- Delayed breeding – Don’t nest until prey rebounds.
During lean prey years, great grey owls may concentrate along coasts, marshes, and meadows where prey is more abundant. They are nomadic and may wander outside of usual range in search of better hunting grounds.
Comparison to Other Owls
While diet varies regionally, great grey owls generally consume higher proportions of mammalian prey compared to sympatric owl species. For example:
- Great grey owl – Up to 99% mammals.
- Great horned owl – 33% mammals, 39% birds, 22% invertebrates.
- Snowy owl – 35% lemmings, 35% birds, 24% other mammals.
- Northern hawk owl – 42% birds, 37% mammals, 15% invertebrates.
- Barred owl – 89% mammals, 7% birds, 4% invertebrates.
The great grey owl’s heavier reliance on rodents reflects specialization in hunting these prey species. Their adaptations give them a distinct advantage hunting in open northern forests and tundra habitats.
Owl Species | % Mammals in Diet | % Birds in Diet | % Invertebrates in Diet |
---|---|---|---|
Great Grey Owl | Up to 99% | variable | variable |
Great Horned Owl | 33% | 39% | 22% |
Snowy Owl | 35% | 35% | N/A |
Northern Hawk Owl | 37% | 42% | 15% |
Barred Owl | 89% | 7% | 4% |
Conclusion
In summary, great grey owls are highly specialized hunters of small mammal prey such as voles, lemmings, pocket gophers, and deer mice. They use their keen hearing and vision to hunt rodents day and night in northern forests and meadows. Great grey owls will also prey opportunistically on birds, hares, weasels, and even ducks. Their unique adaptations allow them to thrive in cold northern regions with fluctuating prey.
However, great grey owl populations are vulnerable when prey populations crash. They may irrupt outside normal range or exhibit low breeding rates during lean years. Conservation of boreal forests and sustained rodent populations are key to ensuring the continued survival of these fascinating raptors throughout their northern range.