Great Horned Owls: the nesting season begins!

February 17, 2022


It’s that time of year again- breeding season for Great Horned Owls here in Montana! These birds have already started nesting and laying eggs in the southern parts of their range, like Florida and Georgia. Usually, Great Horned Owls will lay their eggs from mid-February til late March. Typically they will only have one brood (or set of eggs/chicks) per year, though some pairs might re-nest if their eggs fail before hatching.


Adult Great Horned Owl perched on a snow-covered branch
Great Horned Owl

Often, the male and female will stay on their territory year-round. We’ve been observing our resident Great Horned Owl pair on and off all year, and they can often be seen throughout the year on ORI’s Live Great Horned Owl Cam.


First step: picking a nest


Great Horned Owls, like most other owls, don’t make their own nests. Instead, they will usually take over an old stick nest built by a raptor (commonly Red-Tailed Hawks). In general, Great Horned Owls will use a wide variety of different nesting locations. If there are old Red-Tailed Hawk, crow, heron, or squirrel nests, they’ll pick those. But, you may also find them nesting in tree cavities, on cliffs, in abandoned buildings, or on platforms or ledges—they are very adaptable!

The pair may alternate roosting at different nesting locations for a couple months before they decide which nest they will use for the breeding season. It’s not known if it’s the male or female who makes the ultimate decision.


On the February Winter Raptor Survey, we observed an incubating Great Horned Owl hunkered down in a stick nest in a cottonwood tree—and, on either side (some distance away) were perched two Red-Tailed Hawks! We surmise the Great Horned Owls took over the old Red-Tailed Hawk nest from the previous year, and the hawks were not quite ready to give up their prime nesting site! However, since the owl was already there and incubating, the hawks will have to find another nest site this year.


Laying Eggs


A female Great Horned Owl will usually lay anywhere from 1 to 4 eggs, most commonly 2. The eggs are laid anywhere from 1 to 7 days between (commonly 2 days). They are dull white, with a coarse, almost roughened, surface, and weigh about 50 grams (just under 2 ounces), which is roughly 3.3% of the female’s body weight. Size-wise, they’re on average 56 by 47 mm (2.2 by 1.8 inches).


Two Great Horned Owls are camouflaged in a tree.
Screen-shot taken by an explore.org live cam watcher. Can you spot both of the Great Horned Owls?

The eggs are incubated by the female, and she starts immediately after laying her first egg. She’ll be on the nest incubating for about 30 to 37 days (the average is 33). While she’s on the nest, the male will bring her prey he’s caught each night.


The female Great Horned Owl stays on her eggs in all types of weather, come rain, shine, or blizzard. One study found that even when temperatures reached below -33 degrees Celsius (-27.4 degrees Fahrenheit) the female was able to successfully incubate her eggs.


Watch nesting Great Horned Owls live


Watch our local Great Horned Owl pair on the explore.org live cam! These owls haven’t chosen their final nesting site yet, and have been seen roosting in a few different potential nesting locations over the last few weeks. Once they’ve made their decision we’ll have the cam moved in order to watch the nesting season from start to finish.

 

Learn more about Great Horned Owls on the ORI website: Great Horned Owl (Bubo virginiaus)


Breeding information from All About Birds and Birds of the World:

Artuso, C., C. S. Houston, D. G. Smith, and C. Rohner (2020). Great Horned Owl (Bubo virginianus), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.grhowl.01


A Great Horned Owl perched on a branch starting straight ahead. It looks "grumpy"
Great Horned Owl. Screenshot taken by a live cam watcher.

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