Science of the Seasons: Whoo goes there? Great horned owls often heard before seen

By Dr. David Wartinbee, for the Redoubt Reporter

Photo courtesy of Dr. David Wartinbee. A great horned owl is silhouetted in a tree. The birds have excellent camouflage. Often their hoots are heard before they are seen.

On a recent evening, as I was watching the end of a cold, beautiful sunset, I noticed a large bird land in a tree in front of the house. From its broad wings, short tail and large size, I was pretty certain it was a great horned owl. Sundown is when they are fairly active as they survey for their next meal. With binoculars I could make out some of its mottled coloration and the all-important feather tufts that give it the “horned” name.

Great horned owls are fairly common here on the Kenai Peninsula and can actually be found all over North and South America. So they are well-known throughout the country. They are one of the larger owls, with a wingspan of almost 5 feet, and they weigh 4 to 6 pounds. That may seem light because they have a barrel-shaped body and their feather fluff-up makes for an impressively large-sized bird.

These predators will take just about any animal they can capture, including grouse, crows, squirrels, marmots, hares, voles, weasels and even fish. In some parts of their range they are known to take bats, reptiles and amphibians. Great horned owls are also a major predator on young raptors, like osprey. They are able to take on more formidable prey because of their large and powerful talons. Some prey items are eaten on the ground, while smaller rodents or birds can be carried to a perch for a more leisurely repast. These owls are not above taking carrion or road kill, too. Because of the willingness to take animals off the roads, younger owls often become road kill themselves.

With the current high numbers of varying hares on the peninsula, great horned owls have probably been feeding well for the past couple years. Recently there have been reports of large local populations of redback voles, so their good food fortunes continue.

Great horned owl food choices remind me of a favorite children’s book called “Owls in the Family” by Farley Mowat. In the story, the two pet great horned owl return to an open porch window with their nightly prey until one flies in with a freshly killed skunk. The family was no longer amused! While that is just a story, great horned owl are actually the only known avian predator of skunks. One western owl nest was found to have remains of more than 50 different skunks. Apparently, owls are not put off by the powerful skunk odor.

These large owls are the very earliest nesters in Alaska. In December and January they will be heard calling and hooting as preliminary mate and territory selection begins. The calling causes gatherings of owls and on one occasion I was able to spot six of the eight birds I was hearing around my house.

By March, the calling will be in earnest, mates will be chosen and territories will be established. Interestingly, Toby Burke, from the Kenai National Wildlife Refuge, tells me that during his spring owl surveys, great horned owl will call actively until the temperature drops below 10 degrees. At that point, the owls apparently go into energy-conservation mode and call less frequently until the temperatures rise again.

Egg-laying begins by April and the brooding by the female follows. These owls are nesting when it is still very cold and there is a lot of snow on the ground. The big job for the male is feeding the female as she broods the clutch of two to three eggs. Once the eggs have hatched and can be left alone for periods of time, both parents will help feed the hungry young.

Great horned owl do not usually build their own nests but, instead, will renovate one built by another bird. They often use nests built by crows, ravens, eagles or hawks. One March in the Chesapeake Bay area, I spotted a brood of ready to fledge owls in a nest I had seen osprey using the previous spring. Interestingly, there was an adult osprey perched nearby, hanging out and waiting for the interlopers to leave the nest so the osprey family could move back in.

Sometimes one can see crows or other birds mobbing a great horned owl they have discovered. They dive at the owl and harass it as much as they can, perhaps in an attempt to drive it out of their area. On a couple occasions, I have witnessed crows following an owl as it tried to find a more secluded perch. Along the way the crows were plucking feathers from the head and back of the fleeing owl. Lest you feel too bad for the owl, remember that they are one of the major predators on young crows. Turnabout is fair play!

As previously mentioned, owls eat a variety of animals and often swallow smaller prey whole. Later on, after digesting the usable nutrients, they regurgitate the remains in the form of a “pellet.” These pellets are often left near their roosting or nesting spots. Researchers have examined these pellets to look for hair, bones and different rodent skulls as a record of their varied diet.

Great horned owl are a beautifully camouflaged owl with mixtures of brown, gray and black mottling. Their distinctive brown facial patch, large-sized yellow eyes, hornlike feathery ear tufts and loud calls make them easily identified. While being heard more often than seen, these stealthy, nighttime hunters are frequently patrolling our yards and fields.

David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the biology of the Kenai River watershed.

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