Tuesday, June 30, 2020

Great Gray Owl: One handsome bird

If nature were a fashion show, the Great Gray Owl might qualify as the most handsome owl, with its grey mottled plumage, inflated bonnet like head, expansive facial disk, penetrating yellow eyes, white mustache and a look of perpetual surprise on its face. And yet the great gray is a bag of bones only half full, with its skeleton dramatically smaller than the large physical appearance created by the fullness of its plumage. 

The Great Gray is not as heavy as the Snowy Owl or the Eurasian Eagle Owl, and it lacks the incredible crushing power that the talons of the Great Horned Owl possesses, but in terms of length, it is the largest owl in the world, averaging two to three feet in length, but only one and a half to four pounds in weight, with a wing span which can reach five feet. As with other birds of prey, females are slightly larger than males.  

Owls have been around for millions of years, and as the purest natural predators, have evolved to fill almost all raptor size slots from the very smallest, such as the elf owl, to the very largest, the Eurasian eagle owl, with only eagles being larger. Owls have also developed to fill almost every major habitat from desert to meadows, and mountains to deciduous forest, boreal, taiga and tundra. The great gray is the most widely distributed of the large owls, being found in Alaska, all over Canada, except the eastern maritime provinces, and all over eastern Europe through western Asia.

Great grays do not build nests, either taking over abandoned nests built by other raptors, or even squirrels or often in snags, the roundish uneven bowl at the top of the trunk of a wind snapped dead tree, or in a crotch formed by branches. Mating takes place between March and May, depending on climate and latitude. The female will lay up to 4 eggs, sequentially, about one a day, incubating them for about 30 days, and the young start to branch or fall out of the nest two or three weeks after birth, and start flying about 6 weeks after birth. Branchers who fall to the ground will either climb back up using beak and talons, or will be fed on the ground by mom until they fly or a predator discovers them. The male brings food continually to the nest throughout this process. 

Great grays eat mainly smaller birds like thrush, grouse, quails, ducks and small hawks, as well as  rodents, from lemmings to hares, moles, voles, shrews and even small weasels. Predominant prey depends on habitat and what’s available.

Great grays are less territorial, at least compared to predators like great horned owls. Grays move around and stay in areas where prey is most abundant, moving again when prey becomes scarcer. They’ll roost at the edge of damp meadows or swamps, where water is available, and prey may be more abundant. Grays will leave areas where the snowfall becomes so deep, it frustrates winter hunting, or move to lower elevations where the snow fall is shallower, or to where the cold is less intense. 

Pockets of Grays will develop and interbreed in areas like Yosemite, becoming somewhat isolated, setting up sub species. Grays will generally not attack great gray intruders, though females will be aggressive against any passing or nearby threats to nestlings. Defensive posture includes puffing up the plumage with expanded wings to exaggerate size, as well as loud bill clicking. In addition, great grays tend to sit quietly when humans show up, in the hopes of not being spotted, so it is possible to find these owls and photograph them.

Great grays hunt by perching on posts or branches and listening.  Great grays have asymmetrical ears, unevenly situated on the sides of their skull, one slightly higher than the other, such that the wide facial disk directs sound to ears which receive the sounds created by the movements of a small rodent, who may be well below snow cover, at minutely staggered intervals, providing a kind of sonar locating of the prey. Here is where it gets scary!

Owls have binocular vision like humans do, but the proportion of eye size to skull size is much greater than it is in humans, one reason their visual acuity is far superior to ours. If your eyes were as proportionately as large as a great horned owl’s eyes, your eyes would be the size of oranges! In addition, owl eyes are not spherical like human eyes are, and they can’t turn or roll their eyes. When the owl adjusts the direction and pitch of its face in an attempt to synchronize the sounds reaching their ears, the fact that owls cannot turn their eyes, means they must be staring straight at the location from which the sounds are emanating. This is why owls have evolved to be able to rotate their heads 270 degrees, allowing them to remain visually motionless, unlikely to be spotted, while still being able to see in nearly all directions. It gets worse for their unfortunate prey.

The great gray can hear rodents at about 100 yards away that are under two feet of snow. When the owl lifts off its perch and flies or glides in the direction of the sounds, they continue triangulating the location of the rodent, and of course the rodent, feeling secure in its snow tunnel, has no clue what is about to happen, which is when the owl plunges feet first through the snow and grabs the hapless vole. 

In fair weather without snow cover, the great gray, like the snowy owl, may fly or glide low over the meadow, hoping to see or hear movement, upon which it will pounce. The only major predator of an adult great gray is the great horned owl. Nestlings may be taken by smaller climbing predators or even black bears.

Clear cut forestry is detrimental to Great Gray habitat, unless it is selective and leaves dead trees and snags in place, giving the owls both nesting and perching areas and clearer sight lines. For similar reasons, stripping the land for cattle raising, or using rodenticides on farm land is also detrimental, as the biomagnification of toxins through the food chain may prove fatal to the owl.

Portrait photo by Anne Fraser, photo from Kenai Penninsula by Steve Hall, pastel by Wendy Hall. Courtesy of the Adirondack Wildlife Refuge and Rehab Center

 

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Steve Hall

Steve and Wendy Hall run the Adirondack Wildlife Refuge and Rehab Center in Wilmington. They've been rehabbing and releasing wild animals for over 45 years, specialize in predators, keep wolves as the cornerstone of their educational program, and have lived in the Adirondacks for the past 20 years. The Adirondack Wildlife Refuge became a non-profit about 10 years ago.

Visit www.AdirondackWildlife.org to learn more.




8 Responses

  1. MITCHELL EDELSTEIN says:

    Steve,

    Any explanation of the huge increase in the chipmunk population this year?

    • Boreas says:

      Mitchell,

      Anecdotally, here at Chez Boreas it seems to be the result of lack of predators and a very good acorn crop last year.

  2. My guess is that we had very good acorn harvest last Fall, good snow cover to insulate dens, healthy moms had larger litters with better survival rate, but also with the quarantine, we’re all spending more time outside up here, and we’re noticing more of what goes on routinely, while we’re usually out making a living.

    • MITCHELL EDELSTEIN says:

      Definitely not noticing more because of COVID, real increase in numbers, activity and garden predation. I wonder why no similar increase in Red Squirrels.

      • Boreas says:

        Perhaps chippers multiply faster, thus giving them a step up on the competition.

        • Suzanne says:

          Also, Red Squirrels are perhaps somewhat less visible because they tend to stay high up in the tall pines, while chipmunks come right into the house and run across your toes while you’re sitting on the front porch.

  3. Bill Ott says:

    With the many articles like this in the Almanack, this publication is now or will soon be (with its search box) an Adirondack encyclopedia. The only problem I have is all the references to my wife in the first paragraph (“inflated bonnet like head, expansive facial disk, penetrating yellow eyes, white mustache and a look of perpetual surprise on (her) face”). None he less, I still say that I learn more about the Adks from these pages than I do from mindlessly bumping around the forest looking for some sort of solitude.

  4. Amazing article as they all are! Thank you for bringing us outside the insect arena.

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