Friday, January 29, 2016

It's nesting season for Great Horned Owls!

Post contributed by Maggie, seasonal Natural Resources Technician:

It’s my favorite time of the year!  It’s the time of year that you can expect to hear Great Horned Owls (Bubo virginianus) beginning their nesting season.  Great Horned Owls (GHO) are one of the most common owls in North America, and can coexist very closely with humans in the city.  They are not only one of the earliest nesting birds in Minnesota, but also in the Americas.  Usually by this time of the year (January-February), the male owl has established his territory and found his mate.   

GHOs have great camouflage!
Male and females begin their mating rituals by calling to one another once they have found a nesting location.  If you listen closely to their calls, you can easily distinguish between the male and female: the male has a much lower pitched voice than the female does.  It’s also thought that female Great Horned Owls only call during the mating and nesting seasons.   

Adult & Juvenile in nest
Great horned owl pairs keep the same territories year-to-year, and mate for life.  Great Horned Owls are found in so many different habitats that their nests can be very diverse.  They don’t usually make their own – instead, they adopt other large birds’ nests, nest in live tree cavities, snags, or in human-constructed nest boxes.  Great Horned Owls have even been known to make their nests on the ground in parts of the prairies of Canada and the Western US.           

The female owl will usually lay 3 eggs, but can lay up to 5 depending on the year and prevalence of food.  She lays one per day and begins incubating the eggs as soon as they’re laid.  The female doesn’t leave the nest for long periods of time due to the cold weather during the incubation period, and is brought food by the male. Eggs are incubated for a period of 30-37 days.  Similar to other raptors, the owlets often hatch on different days and there is usually a noticeable size difference amongst them.  Typical broods of Great Horneds in our area include 1 to 2 fledglings, but I’ve seen up to 3 survive during a good food year!  Once the owlets have hatched, the female and male take turns catching prey for their young.  The female owl usually stays in the nest when she’s not hunting, and the male can often be seen perched nearby.    

The owlets begin branching (leaving the nest and testing their wing feathers) within 6-9 weeks.  During this period, the adults will still bring food to the fledglings, but after a few months, the new owls are on their own!  They will stick around their parents’ territory for the summer, but then need to find their own territory.  When they reach 2 years of age, they will begin mating. 

Keep watch for signs of this common, yet well camouflaged and hard to spot bird in our parks!  Common signs of an owl nearby are very vocal groups of crows, whitewash on trees (the droppings often left behind on favorite perches of raptors) and agitated songbirds -- maybe if you’re lucky you’ll hear them calling and be able to spot one!

Check out this page for more owl vocalizations and other info about GHOs!