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 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.