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Scientific name: Bubo virginiarus
Common name: 
Great Horned Owl

(Information for this species page was gathered in part by Timothy Burg (2001), Amy Weister (2003), and Steven Powell (2004) as part of their work in Biology 220W at Penn State New Kensington.

Appearance
The great horned owl (Bubu virginiarus) is a large, nocturnal predator that is frequently heard and occasionally seen on our Nature Trail. The great horned owl is between 18 and 25 inches long with an additional 7 to 10 inches of tail. It has a wing span of 3 to 5 feet! Females are up to 20% larger than males and may reach weights of nearly 5 pounds. The owl has large, yellow eyes and powerful, taloned feet that are feathered to the ends of the toes. Both male and female great horned owls have similar color patterns: dark, mottled backs and lighter colored bellies with white throat feathers and row after row of laterally arrayed dark bars. This color pattern provides excellent camouflage for the bird in its leaf-filled hunting and roosting habitats. The exact colors of the great horned owl vary over its geographic ranges and from habitat to habitat. The birds may be dominantly reddish brown, or gray, or even a startling black and white. All great horned owls, though, have the distinctive ear tufts which gives them their common name.

Call
The call of great horned owl is loud and distinctive and most frequently heard from dusk to midnight and then again at dawn. The males singing to claim and hold their territory make an eerie hoo-hoo hoooooooo hoo-hoo that may carry for miles on a still night.  Females, since they are larger, have deeper voices and make their own array of cat-like meows, dog-like barks, and blood curdling  shrieks. On a still summer night, these owls can generate a never-to-be forgotten concert in the dark shadows of our Nature Trail's forest.  

Range and Habitat
The great horned owl is extremely adaptable to a wide range of habitats. The eight recognized sub-species are found from Alaska and across Canada, over the entire United States, down into the Yucatan of Mexico and even into Central America. These owls may live in deep forests or deserts, in grasslands or farmlands, and even in suburban neighborhoods or city parks. The densest populations of great horned owls are found in the central United States (North and South Dakota, Colorado, Nebraska, and Oklahoma). Owls in the northern parts of their extensive range migrate to the south in the winter but throughout much of  North America the great horned owl is a year-round resident.

Although these animals may live in almost any habitat that provides them with sufficient prey, they do seem to prefer sites with a mix of mature deciduous and coniferous trees that are adjacent to waterways and open zones suitable for hunting. The trees provide the owls with high, concealed day-time roosts and also potential nesting sites. The great horned owl does not, however, build its own nest. Instead, it typically appropriates a suitably sized nest from other owls, crows, hawks, herons, or eagles. It may even take over a squirrel nest in a tree hollow (often after it has consumed the resident squirrels!). Crows are somewhat unique in that they often resist and may even defeat their eviction by a great horned owl. Great mobs of crows may gather to harass and even physically attack the invading owl often resulting in its expulsion from the crow's nesting site. The great horned owl prefers nest sites that are well concealed in dense vegetation or sometimes even wedged onto unapproachable cliff sides or hidden inside caves.

Reproduction and Life Span
Breeding by great horned owls takes place as early as January and may continue on into the spring and summer. Females typically lay between 2 and 4 eggs and both males and females take turns incubating the clutch for the 26 to 35 days required for hatching. Both parents also feed and protect the nestlings and will continue to feed and nurture the fledglings throughout the summer. During this period of time the parents may even switch over to diurnal hunting activity in order to secure sufficient food for their offspring. The mated pair will remain together only during the nesting season and will then spend the remainder of the year apart as solitary hunters. There is a very high mortality rate among the young that continues over the first two years of life. Starvation, accidents, and predation (often by other great horned owls!) greatly reduce the numbers of surviving young. A great horned owl that makes it through these early years of life, though, has a good chance of living quite a long life. In the wild, life spans of 13  years are not uncommon and in captivity, some birds have been said to live for up to 30 years! A mature great horned owl has very few natural enemies (other than other great horned owls and, possibly, Northern Gosshawks) and is protected against legal hunting by both Federal and State laws. Human impacts on this species, though, can be fatal: illegal hunting and trapping, vehicular accidents, and electrocution on power lines are not uncommon fates for a great horned owl.

Hunting Behavior and Diet
The great horned owl is typically a  nocturnal hunter. It can, though, as was mentioned above, switch its hunting patterns to a crepuscular (dawn and dusk) and even diurnal time sequence depending on its nutritional needs and on a site's prey abundance and availability. The great horned owl takes a wide range of mammalian prey (including mice, rats, squirrels, rabbits, and skunks), avian prey (almost any species of bird), and fish and amphibian (especially frogs) prey. They also eat large insects and spiders among an assortment of other invertebrate species. Small prey species are swallowed whole while larger species are taken to a feeding perch where they are torn into smaller pieces and then consumed. The owl swallows feathers, fur, and bones along with the digestible meat and internal organs. These non-digestible parts are then regurgitated 6 to 10 hours after eating. The regurgitant is a compact, dark, gray-brown mass called a "pellet." Examination of these pellets is an excellent way to gather very precise data about the feeding habits of the owl.

Great horned owls have historically been deemed pest species by farmers because of their potential to take chickens, ducks, and other farm animals as prey items. It has been clearly shown, however, that penning these farm fowl up at night is an extremely effective way to prevent potential owl predation. It has been further shown that the impact of an intact population of great horned owls upon an area's populations of mice and rats and other rodents that damage crops and consume stored grain products is of considerable benefit to the overall economy of a agroecosystem.



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