The great grey owl (Strix nebulosa) is a very large owl, documented as the world’s largest species of owl by length. They are found across the Northern Hemisphere, with populations in Canada, Alaska, Northern Europe, Northern Asia and isolated areas of the northwestern United States. Great grey owls are long-lived birds that can survive up to 20 years in the wild.
Typical Lifespan
The typical lifespan of a great grey owl living in the wild is between 5 to 10 years. However, there are records of wild great grey owls reaching 20 years of age.
In captivity, great grey owls appear capable of living even longer than 20 years. The oldest known captive great grey owl was at least 27 years old when it died. With excellent care and protection from predators, great grey owls have the potential to live for several decades.
Mortality Rates Throughout Life
Great grey owl mortality rates are highest in the first year of life, then decrease once the birds reach adulthood.
Nestlings
Great grey owls typically lay 2-5 eggs per clutch in the spring. However, on average only 1-2 owlets per nest will survive to leave the nest, also called “fledging”. Nestling mortality can be up to 70% from starvation, predators, or harsh weather. If the parent owls are unable to find enough food, the younger owlets often die so resources can be focused on the older, larger owlets.
Fledglings
After great grey owlets fledge from the nest around 4-5 weeks old, they remain dependent on their parents for food and protection. Mortality rates remain high at this stage as the juvenile owls learn to hunt while navigating threats from predators. Up to 70% of fledglings may die within their first few months outside the nest.
Juveniles
Great grey owls are not sexually mature until they reach 2 years old. The time between fledging and sexual maturity is considered the juvenile stage. Mortality risks decrease from the fledgling stage but are still significantly higher compared to adult owls. Up to 50% of juveniles may die from starvation, predators, accidents, or disease.
Adults
Great grey owls that survive to adulthood have markedly higher annual survival rates. Studies suggest annual mortality rates of mature great grey owls are around 15%, compared to the much higher rates for young owlets and fledglings.
With few exceptions, causes of mortality for adult great grey owls include starvation during periods of prey scarcity, being struck by vehicles, violent conflicts with other owls over territories, or being killed by larger predators like golden eagles. Otherwise, their advanced hunting skills, large size, and lack of natural predators gives them high annual survival as adults.
Factors Affecting Lifespan
Several key factors influence the lifespan of individual great grey owls:
Food Availability
Abundant food sources leads to lower mortality rates and longer lifespans. Great grey owls primarily hunt small mammals like voles, pocket gophers, mice, and hares. When prey is scarce, owls may starve or die from complications related to malnutrition. Frequent years with prey scarcity can significantly reduce great grey owl numbers and lifespans in the wild.
Predators
Golden eagles are the main predator of great grey owls where their territories overlap. Owlets and fledglings are also vulnerable to predation from pine martens, raccoons, red foxes, bobcats and other birds. Lack of predators, especially golden eagles, likely contributes to longer lifespans.
Weather Severity
Harsh winters with heavy snowfall can limit the owls’ ability to effectively hunt prey and lead to starvation. Late spring snow storms can kill nestlings and fledglings. Great grey owls adapted to milder climates likely have higher survival rates and lifespans.
Disease
Like other birds, great grey owls are susceptible to bacterial, fungal, and viral infections. Examples include avian influenza, West Nile Virus, aspergillosis, and avian pox. While adult owls have higher disease resistance, diseases can still reduce average lifespans, especially during outbreaks.
Human Activity
Human disruption of nesting sites, habitat loss from development, vehicle strikes, or illegal shooting can negatively impact great grey owl numbers and lifespans. However, protected conservation areas with limited human activity support longer-living owl populations.
Territory Quality
Great grey owls with high quality territories have greater access to food resources and nesting sites. This contributes to better breeding success, lower mortality, and increased lifespans compared to owls relegated to poor quality habitats.
Age | Mortality Rate |
---|---|
Nestlings | Up to 70% |
Fledglings | Up to 70% |
Juveniles | Up to 50% |
Adults | Around 15% |
Interesting Facts About Great Grey Owl Lifespans
Here are some interesting facts about the lifespan of great grey owls:
– The oldest known wild great grey owl was at least 20 years old when it was found in Alaska.
– In captivity, great grey owls can live over 25 years with the oldest recorded at 27 years old.
– Lifespans between male and female great grey owls are similar. There is no significant difference between the sexes.
– Adult owls have few natural predators due to their large size. Most owls die from starvation rather than being killed by a predator once mature.
– A 19 year old great grey owl was documented successfully breeding, showing owls can remain reproductively viable even in old age.
– Collisions with vehicles account for a significant number of adult great grey owl deaths as they hunt rodents near roadsides.
– Territory quality plays a major role in lifespan. Owls holding poorer territories die younger on average.
– Harsh winters and heavy snows can rapidly reduce owl numbers through starvation, especially of younger owls.
– Conservation programs aim to improve habitats and reduce disruptive human activity to support longer-living owl populations.
Conclusion
In summary, the great grey owl is a long-lived species capable of surviving up to 20 years in the wild, and over 25 years in zoos. While many owlets and fledglings die young, owls that reach adulthood tend to be very resilient with high annual survival rates. Abundant food sources, high quality habitats with access to nesting sites, and protection from human disruptions and predators are key factors that allow great grey owl populations to maximize their lifespans. With excellent environmental conditions, the great grey owl can maintain stable populations of these magnificent birds surviving and breeding into old age.