Great Gray Owl Leaves Territory To Visit Mackinac Island Nature Notes
By Patricia Martin

It’s winter on Mackinac. The snow is falling, the boats have stopped, and the “ice is made.” It’s the quiet time of year. Few visitors reach our icy shore, fewer still stay, and most of us kind of like it this way.

There is one visitor that I’ve been delighted to see several times. The latest encounter occurred this morning as I was cross-country skiing along North Bike Trail. While gliding through the snow, I looked up and there, silently flying above the path, was a huge owl. It landed on a branch up ahead. As I approached, it flew on, repeating this pattern several times. The wing span of this bird in flight was amazing, almost the width of the trail. This is the second time I spotted a Great Gray Owl. The first was four weeks ago, in the Annex, where it was sitting on a branch near a cottage. During that encounter, it merely sat, staring at me for about 15 minutes as I walked around the house. It didn’t move or fly away. It only turned its head to keep me in view.

Great Gray Owl

I was surprised by both of these meetings, as Mackinac is south of the Great Gray’s normal territory. These are boreal forest birds that usually don’t migrate. This is the largest owl in North America, though the Great Horned Owl is heavier. It’s a long-tailed owl with a large head. It has huge facial disks crossed by a series of dark gray concentric rings, which surround bright yellow eyes. Below its facial disks is a white mustache and its chin is black. Its lower body is heavily streaked and its overall color, as its name suggests, is gray-brown.

The reason that this is not the heaviest owl, though it is the largest, is that to keep itself warm in the far north, it has many layers of feathers. For instance, if you were to touch the head of this bird, you could put your fingers about one-third of the way in before you would reach the skull. The total length of the Great Gray is about 24 to 33 inches and its wingspan is 54 to 60 inches, and with all the feathers, it looks huge. It weighs about 1.7 pounds. (The Snowy Owl weighs about four pounds, and the Great Horned about three pounds, though they’re both shorter in length than the Great Gray).

The only other owl that you might mistake it for is the Barred Owl, which is quite common here. The barred is much smaller, only 17 to 24 inches in length, is browner, and has dark eyes, not yellow. The voice of the Great Gray Owl is a deep, booming series of “hoo-hoo-hooo,” each lower in pitch. It also utters single note hoots.

These large owls normally live and breed in the dense boreal and coniferous forest of the north or along the edges of bogs. Perhaps because of their northern isolation, they don’t seem wary of people. During their courtship ritual, the male performs aerial displays, along with courtship feeding and mutual preening. The pair usually nests in trees 10 to 50 feet off the ground, generally claiming an old abandoned nest of a hawk or eagle. Occasionally they may nest on a stump top, or even on the ground. Their nests are generally a composite of sticks and moss. Scientists have been able to induce them to use an artificial nest site created by topping trees and hollowing out the center of the trunk. Each year the owls produce one clutch of two to four, two-inch white eggs, which the female will incubate for about a month. During this period, the male owl will feed the female and will continue to do so through the small nesting stage. The female will brood the chicks nearly continuously for two weeks and the young are fledged within a month of hatching. The young return to roost in the nest well after departure, and remain with the parents for up to several months post-fledging.

Most owls are primarily nocturnal, but the Great Gray is one of the most diurnal of the owls, which explains why we see them during the day. Their food source is perhaps the reason for their appearance south of their normal range. Rodents, particularly voles, are their preferred prey, though they will also take birds. They commonly swoop down and plunge into the snow to catch the rodents that they detect by sound. Because these owls depend on rodents for survival, a drop in the rodent population creates a need to migrate, or to at least to become a nomad in search of food. This is why birds like the Great Gray and Snowy Owls show up in the balmy south of the Eastern Upper Peninsula.

There are two population cycles that are recognized in boreal small mammals: the four-year cycle among tundra and grassland rodents and a 10-year cycle that is characteristic of the Snowshoe Hares. Why populations of these species explode and crash with such regularity is not clear, but when the populations crash, the result is that there is a southward movement of their avian predators. This fluctuation in rodent population may remind you of the lemmings in the children’s story, the “Pied Piper,” and it surely gave rise to the legend.

It is interesting that we have also seen the Snowy Owl on Mackinac Island this winter, and we just may see them again four years from now. Northern Shrikes, which also eat rodents and birds, have also been seen on the Island. This is not uncommon, however, as they often spend winters in our area.

Owls identify prey by sound with remarkable accuracy. Part of this has to do with the structure of the opening to the owl’s ears. The right and left side ear openings are at different heights. The difference in intensity of the sound received by the ears is used to determine the vertical placement of the sound source. If the origin of the sound is above, it will be slightly louder in the ear with the higher opening; if a sound is straight ahead, the sound intensity will be equal. The clue to determine whether a sound comes from the right, left, or straight ahead comes from the difference in time that it takes for a sound to reach each ear. If the source is dead ahead, there is no time difference. The owl’s ears are linked with specialized cells in specialized sections of the mid-brain. Each cell is sensitive to a unique combination of time and intensity differentials and responds only to sound issuing from one small area of space. It basically maps the sound. In addition, the ruff around the owl’s head acts as a reflector, helping to collect the sound and direct it to the owl’s ears.

One other thing that helps owls in their hunting is the silence of their flight. The silence on the wing comes from the structural modification of the first primary feathers on each wing. The forward edge of the feathers is serrated rather than smooth, which disrupts the flow of air over the wing in flight, eliminating the vortex noise created by airflow over a smooth surface. Except for when they call, you will see an owl before you hear him. In addition, owls have the ability to sit still for long periods of time.

I hope that you get a chance to see one of these magnificent birds, whether it be a Great Gray, a Barred, a Great Horned, or a Snowy Owl. There’s something kind of magical about them.

I am reminded of the following bit of doggerel that I learned as a child. “The wise old owl lived in an oak. The more he saw, the less he spoke. The less he spoke, the more he heard. Why aren’t we all like that wise old bird?”

Trish Martin is a year-around resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.