January is great horned owl month on our mountain. Not only are their hoots the quintessential signature of long, silent, moonlit, winter nights, but they are also more visible in the day time. During the rest of the year I may have an occasional glimpse of one as it flies from a roost, but my best sightings have occurred in January, most notably January 18, 1993 and January 19, 1998. In both instances the mobbing calls of American crows alerted me to their silent, motionless presence.
The 1993 sighting occurred on a windy, 20 degree, sunny morning. I tracked scolding crows to Margaret’s Woods, but I could not see any enemy they were mobbing. Still they persisted, so I finally walked toward them up the Steiner-Scott Trail (a recent logging road that leads to the top of Sapsucker Ridge).
Halfway along the trail, I spotted a large, beige-colored blob on the branch of a tree swathed in grapevines. To my delight that “blob” was a great horned owl, bathed in sunlight and not inclined to fly. I sat below it, my back against a tree, and watched as a pair of black-capped chickadees flew in close to scold the owl. Then a tufted titmouse joined the chickadees as they called a couple feet from the owl’s head. It blinked its eyes open to look and the birds flew off, so it closed its eyes again.
After a few moments, it again opened its eyes and slowly turned its head to the side. The eye toward me watched as I stood up. After I took a couple steps, it flew off.
I was amazed at how perfectly it had blended into the tree branch and grapevines. Without my binoculars I never would have distinguished the owl with its perfect camouflage. I thanked the crows, which for once had had something to crow about.
According to biologist Bernd Heinrich, who studied mobbing behavior while raising an orphaned great horned owl, birds that are permanent residents of an area, such as the tufted titmouse and chickadees I observed, use mobbing to encourage owls to move on. He further hypothesizes that “since crows have conspicuous roosts to which they return each night, the ‘move-on’ hypothesis should apply especially strongly to them. And, indeed, the vigor of the crows’ mobbing in winter is surpassed by few other birds, even in spring.” Furthermore, after analyzing owl pellets in his woods, he discovered that crows were the principal prey item of great horned owls there.
Whether or not our great horned owls prefer crows, mobbing crows again “showed” me great horned owls last January on an inclement morning. A light snow fell as I walked Greenbrier and Ten Springs trails through a forest that had been clearcut seven winters ago. But as I neared the end of Ten Springs Trail, five crows cawed loudly in the uncut forest ahead. I sat down in the heavily wooded hollow and, looking uphill, I quickly spotted the shape of a great horned owl sitting out on the end of a tree branch. It looked as if it were unbalanced, an extension of a branch that leaned but, in fact, the branch had a projection against which the owl was braced.
I sat and watched for fifteen minutes as two crows remained nearby, occasionally emitting low noises of approbation in their throats. Then I spotted a second, slightly larger owl sitting tightly against the tree trunk. No doubt it was a pair–the larger female against the trunk, the smaller male out on the branch. I’d never seen a pair before so I continued watching them until I was too stiff and cold to remain any longer.
As I stood up, stretched my cramped legs, and continued my walk, the male, which had had its head turned away from me the entire time, finally looked down at me. The female never moved. In both owls, it had been their ear tufts that had made it possible for me to first pick them out despite their frozen stances and excellent camouflage.
Heinrich also speculates on the use of ear tufts. Fifty of the world’s 131 species of owls have them, yet no one is sure what function they serve, if any. In the case of Heinrich’s captive great horned owl, Bubo, he says that “he has a fondness for perching on broken-off tree trunks, where he quite effectively impersonates the top of the stub” and wonders if the reasons for ear tufts could be that they mimic the ears of mammals which helps them in their threat displays, they serve as short-range species-recognition marks, and/or they provide added camouflage. Perhaps ear tufts helped to camouflage Bubo but not the wild owls I observed.
I assumed that the pair I saw was the same couple that hooted throughout the winter near our home since a breeding pair needs a square mile of good territory, which is exactly what we own. On February 13 and 14 a pair called from trees on top of Sapsucker Ridge in early evening, and we could easily see them with our binoculars. By February 18 they had moved to the small woods above our garage and hooted most evenings and early mornings until March 16. The female hoots are shorter and higher pitched than those of the male. Researcher John T. Emlen had sharp enough ears to detect grunting noises the male makes before he hoots and in between hooting to stimulate the female to hoot. The female hooting in turn stimulates the male to continue hooting. All of this is part of the annual courtship ritual between birds that mate for life.
Solitary hooting by males is done to advertise and defend their territories, which they hold on to throughout the year. Most great horned owls remain in the same area where they hatched unless food is scarce. Then the young may move on, as far as 837 miles in one case. But established pairs may choose not to breed if food is scarce because faithfulness to their territory is stronger than the urge to breed in most paired great horned owls.
When there is enough food, courtship takes place mostly in early January and February evenings and includes calling, displaying, mate-feeding and allo-preening. First the male approaches the female by hooting and landing on perches close to her. She may answer him if she is interested. He then performs such displays as fluffing his body feathers, partly spreading his wings and bowing, walking and hopping on the ground, and/or throwing his head back and repeatedly snapping his bill. If she doesn’t fluff her feathers or snap her bill at him–both signals that she is not interested–he sits on the same perch with her, gradually sidling closer, until they preen each other by pecking at the feathers around their mate’s bill and/or head and sometimes emitting a variety of barks, screams, whistles and hoots. Then both hop and bow, and occasionally a male brings in food for them before they mate. After mating, the pair often roosts together during the day like the pair I observed last January.
Great horned owls never build their own nests. Instead they occupy the used nests of red-tailed hawks, crows, ravens, herons or squirrels. Last winter I examined dozens of old squirrel nests in search of nesting great horned owls but never found any. Since they occupy their nests and lay their one to four white eggs from mid-February to early March in Pennsylvania, deserted nests are easy for the owls to preempt. The female, occasionally relieved by the male, incubates the eggs from 28 to 30 days, but once the eggs hatch, the female keeps the young warm while the male provides food for the family.
The young hatch over several days, according to the order in which the eggs were laid. if food is abundant, all of them survive and thrive. If it isn’t, the largest owlet is fed first and competition is fierce. Often the youngest (and weakest) die.
At two weeks of age their eyes are open, at three brooding stops, at four to five weeks they can move about the nest, and at six to eight weeks they leave the nest, perching on nearby branches where their parents continue to feed them. When they are nine to ten weeks old, they attempt to fly and gradually, after ten more weeks, they have learned to fly and been taught by their parents to hunt well enough to disperse, although half of all young do not survive their first year.
Humans have been their most implacable enemies. Because great horned owls eat popular game species such as ruffed grouse, eastern cottontails and ring-necked pheasants in Pennsylvania, persecution of great horned owls in the form of bounties were in place from 1937 to 1941 and from 1944 to 1966. The Federal Migratory Bird Treaty Act of 1972 forbade the taking of all raptors including great horned owls, and since that time their numbers have increased.
Great horned owls are opportunistic feeders and tend to eat whatever is available including rabbits, foxes, porcupines, skunks, other owls, hawks, crows, feral cats, mice and rats. They fish in water up to their stomachs for fish, turtles, crayfish and frogs, although Heinrich’s captive Bubo distinguished between wood frogs, which he relished, and bullfrogs, which he disliked.
One researcher in Wisconsin watched as a great horned owl perched on a tamarack tree, bobbed its head, flew off into a gradual climb, flipped back in midair, and grabbed large, chunky beetles, which it carried back to its perch to eat. Another owl was observed as it ripped a muskrat from a trap and still another tried to grab a raccoon from a hunter’s shoulder. Bubo dined happily on fresh kills made by Heinrich’s cat–mice, voles, shrews, and songbirds–and on fresh road kills collected by Heinrich. Heinrich also fed him red squirrels that he shot.
Years ago, when we raised Muscovy ducks, we arrived home after sunset and watched a great horned owl trying to fly off with our alpha male Muscovy named Big John. Big John flapped valiantly as the owl aborted a couple liftoffs before giving up. In the end, though, it was a raccoon that wiped out all 27 of our ducks as they roosted in the barn.
A food study done in Pennsylvania from 1965 until 1986 by biologists Wink, Senner and Goodrich analyzed owl pellets from 17 counties throughout the commonwealth and found that although eastern cottontail rabbits were a favorite prey item of great horned owls (15%), ruffed grouse prey ranged from 9% in northwestern Pennsylvania to 4% in southeast Pennsylvania and pheasants a mere 3%. The overwhelming favorite prey, however, were Norway rats (24%). But if the diet was based on the weight of the prey, opossums constituted 33%, rabbits 28% and Norway rats 12%.
The rats are an indication of how popular farm habitat is with great horned owls. According to a study carried out by Yahner and Morrell from 1986 to 1989 in south central Pennsylvania, great horned owls hunted most extensively in agricultural areas and adjoining woodlands. In fact, the more fragmented the landscape, the better the opportunities for great horned owls.
Because they will eat almost anything and live almost anywhere–from Arctic Canada and Alaska to the southern tip of South America–great horned owls will survive and thrive long after specialists have gone extinct. That’s good news for those of us who define our winter nights by the hooting of great horned owls.
Marcia Bonta 
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