Age/Mortality – The first year of life is the hardest to survive for Great Horned Owls and depends heavily on food abundance. Once they reach adulthood survival rates are very good. They have no natural predators as adults, so most owls admitted to rehabilitation centers have human-caused problems: hit by car, shot, electrocuted, caught in barbed wire, caught in leghold traps, west nile virus, poison, etc. Natural causes of death include starvation and hunting injuries.
The oldest known wild Great Horned Owl was 28 years old, but in captivity they can live even longer. A captive female at the San Francisco Zoo turned 50 in 2012.
Weight – Females are bigger and heavier than males, but size varies greatly throughout their range. The largest Great Horned Owls are the pale subarcticus subspecies birds in Canada, with males from 2.3-3.0 lbs and females 3.0-4.4 lbs. Some of the smallest are the pacificus subspecies birds in central and southern California, with males from 1.5-2.8 lbs and females 1.8-2.8 lbs. Iris is a well-fed, fairly large female. She was weighed in the spring of 2011 and was about 4.4 lbs (2000g). Rusty has not been weighed since he came to Houston.
Diet – Great Horned Owls eat almost anything that moves, and will even eat carrion if need be. They are carnivores, however, and don't eat seeds, bread, or anything other than meat. A partial list of food items they have been documented eating includes: hares, rabbits, mice, coots, and ducks (these are generally staples of their diet); skunks, ground squirrels, rats, muskrats, tree and flying squirrels, woodchucks, prairie dogs, raccoons, house cats, very small dogs, porcupines, voles, kangaroo rats, pocket gophers, moles, opossums, chipmunks, shrews, bats, bobcat, weasels, geese, herons, loons, mergansers, grebes, rails, pigeons, starlings, other owls up to and including Great Horned Owls, Osprey, crow, raven, hawks, pheasant, bobwhite, Rhinocerus Auklet, chickens, grouse, shorebirds, gulls, egrets, bitterns, woodcocks, doves, woodpeckers, songbirds, lizards, snakes, frogs, toads, salamanders, worms, crayfish, insects, centipedes, scorpions, suckers, chubs, perch, bluegills, sunfish, catfish, bullheads, and eels.
Basically they eat whatever is handy, and have one of the most diverse diets of North American owls. This helps them to be able to live in a wide variety of habitats, including cities.
Pellets – Like other owls, Great Horned Owls eat fur, feathers, and bones along with the meat and organs. And like other owls, their stomach acid isn't acidic enough to digest the bones, fur, and feathers, so they throw up pellets once a day that consist of these indigestible goodies. (Some other owl species throw up pellets twice a day.) Pellets are coated with a slimy layer of mucous to help them slide up and out.
Nesting – Great Horned Owls, like other owls, are clueless about building nests. They use other available structures to nest in, which include stick nests of hawks and crows; squirrel nests; small caves, ledges or crevices on cliffs or in quarries; sometimes on the ground in the entrance to a den; bridges, power lines, barns and old buildings, large flower pots on balconies, and a variety of artificial nests put up by humans from old tires to laundry baskets.
Eggs and Incubation – They most often lay 2-3 eggs, with incubation usually starting when the first egg is laid. The female develops a brood patch and does the incubation, which lasts 30 or more days. The average number of days is 33.
Fledging – Owlets grow very fast and eat like pigs. They are ready to start "branching" out onto adjacent branches or the side of the nest sometime after 6 weeks of age, even though their head and bodies are still fuzzy. They aren't flying well until 10-12 weeks of age. This is a very vulnerable time of their life.
Can they turn their heads all the way around? Yes and no—it depends on the starting point. If an owl starts with its head in the forward position, it can easily rotate to look directly behind itself. If startled while in this position the owl can crank its head further until it's almost over the other shoulder...in the ballpark of 270 degrees. But they normally don't do more than look over their back under normal circumstances.
But if the owl starts with its head rotated to the back over one shoulder, it can easily turn its head back to the front and then to the back over the other shoulder. So yes, they can easily turn their heads all the way around if they start out facing backwards. This means the can see all the way around themselves without having to move their bodies at all.
On the flip side, their eyes are so large they cannot move them at all in their sockets like we can. So they NEED to be able to turn their heads farther. They accomplish this by having LONG necks (14 cervical vertebrae as opposed to 7 in humans). They just have long, fluffy neck feathers and keep their necks squished down into an "S" shape so it looks like they don't have much of a neck.