by Lisa Bate
Few birds have the incredibly intense reputation of the Great Horned Owl. Large, tough, strong, and capable of silent flight, these birds are hunting sleuths. Their powerful talons can apply 28 pounds of force while holding their prey. Their sharp beaks are lethal and effective for snapping spinal cords and ripping flesh apart. They feed upon the widest variety of prey of any American owl. Their diet varies depending on where they live, but prey items can include rodents, hares, rabbits, reptiles, arthropods, ducks, coots, songbirds, other raptors, cats, and even skunks. Owls cannot digest bones, however, so need to regurgitate pellets regularly in order that sharp items do not pass through the digestive track.
Great Horned Owls are such a formidable predator that people use plastic replicas of them to deter other birds from landing on power poles and buildings. At the Jewel Basin Hawk Watch site, a plastic owl is “perched” on a tree on the ridge. Other raptors see the plastic owl as a threat and come in to take swipes at it. This provides observers with incredible entertainment, but more importantly, a close-up view of migrating raptors for species identification.
Great Horned Owls have acute hearing, but it is their vision that really sets them apart. They have enormous, gorgeous, eyes, larger than all other owls. Human eyes would be the size of grapefruits if we had the same proportion of eye to skull volume. They cannot move their eyes, so turn their heads instead. They can rotate their heads up to 280 degrees. The back of their eyes are specially equipped with high numbers of specialized photoreceptors called rods. These receptors allow them to see extremely well in low-light conditions. This enables them to hunt at night and during crepuscular hours (dusk and dawn), when their prey cannot see them coming.
The other unique adaptation that allows Great Horned Owls to be such effective hunters is their wings. They fly silently. This allows owls to grab their prey before they even know the owl is near. We can hear most birds flapping as they fly overhead because the air rushing over the surface of the wings causes turbulence, or noise. Owl wings are different. The tips of their primaries, or wing tips, are soft and serrated (like a comb). This breaks up the turbulence by allowing the air to pass through the tips of the feathers.
Great Horned Owls have the most extensive range of any American owl, and are equally at home in forests, as they are in suburbia, grasslands, and deserts. They range into Alaska and Canada in forests to tree line, and south into Central America and even parts of South America.
Great Horned Owls get their scientific name, Bubo virginianus, from the Latin word Bubo meaning “owl” or the Greek word for “eagle owl”. Virginianus is in reference to the state of Virginia where the first specimen was collected. These are large, stocky owls with females standing nearly 24 inches tall with a wingspan of 56 inches. The males are slightly smaller. Much of their size is simply “fluff” though, as they only weigh about 3 pounds. They are cryptically colored: mottled gray-brown on their backs and rusty brown and heavily barred on the chest and belly. They have yellow eyes and a black bill. The most distinguishing characteristic of these owls, however, are their “ear” tufts, which actually have nothing to do with hearing. Long-eared owls also have ear tufts, but are considerably smaller and thinner.
Their hooting calls are the makings of mystery stories that occur in the dark. In reality though, they hoot to defend their territories and attract mates. They can mate for life. Their calls are soft, deep hoots (https://www.allaboutbirds.org/guide/Great_Horned_Owl/sounds) with an irregular rhythm: hoo-h’HOO-hoo-hoo. The female calls are noticeably higher than the male calls. The young “screech or scream” for food, likely leaving many a camper wondering what creature or space alien was around. Campgrounds are a great place to listen for owls as they prey upon all the small rodents that thrive on food morsels dropped by campers.
Great Horned Owls are great at many things, but nest building is not one of them. They most commonly use tree nests of other species. They will also nest in cavities in trees, snags, cacti, on cliffs, buildings, artificial platforms, or even on the ground adding little, if any, materials. Great Horned Owls will nest earlier the further north they live. Incubating females can maintain eggs at 98.6◦ F even when the ambient temperature is nearly -30◦ F due to their soft insulating feathers being so efficient.
In Montana, Great Horned Owls begin nesting in February, and courtship hooting can start as early as January. They typically lay 1 to 4 eggs with the first egg being the largest. Eggs hatch after about 30 days asynchronously, meaning not together. This results in the first-born chick, being larger than the other chicks. When food is plentiful, all chicks may survive to fledge. When food is scarce, however, only the oldest (largest) chicks survive as they easily out compete their siblings for food. The chicks fledge in 5-7 weeks.
Great Horned Owl populations throughout the state and world are stable. In some areas, however, owls are vulnerable to pesticide or rodenticide poisoning as folks try to get rid of mice, voles, or gophers in their yards or fields. This in turn, poisons the foraging owl. A safe alternative is to raise a hawk pole from which owls can hunt, or use snap traps, to control rodent populations. Another risk to owls is vehicle collisions. Roads function as a type of smorgasbord with all the rodents crossing them at night. Driving slower at night can help reduce vehicle collisions with owls and all wildlife species. So give them a “brake” and watch for this magnificent predator of the night!