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Species profile: The white shadow, Snowy Owl
Wintering Snowy Owls often seem tolerant of humans, but looks can be deceiving
Published: November 1, 2001 Heavily built, with luminous golden eyes, broad, rounded wings, and luxuriously covered from head to claw with feathers the color of wind-driven snow, the Snowy Owl has to be one of the most beautiful birds in the world.
And since in winter it’s known to sit for hours at a stretch — on fence rails, lampposts, haystacks, or sand dunes — birders consider it one of the most cooperative species as well.
Yet encountered at a different place, at a different time, the same bird would have to be called one of the most aggressive, as Alfred M. Bailey discovered early last century. Hiking with his dog Jerry in the Arctic tundra in 1926, Bailey stumbled upon a Snowy Owl nest that he soon discovered contained young. The nest was defended by an adult male that was anything but docile. “The old male, a fine white specimen, kept circling overhead, occasionally making a hoarse who-who. He would sail up against the wind, then circling, would dart within a few feet of us, paying special attention to my Airedale.”
Swooping down with talons curled, the owl struck Bailey’s dog, knocking the animal to the ground and bloodying its ear. “The speed with which the owl could drop from the sky on folded wings was a revelation,” Bailey reported. “Time and again I found myself dodging from his fierce onslaught.”
Protective of their young, Snowy Owls have been known to attack intruders as far as a kilometer from the nest. Such aggressiveness is a fact of life on the owl’s breeding grounds, which stretch from northern Alaska and the Canadian Arctic Islands to northern Quebec and Labrador. The region is home to such predators as Arctic foxes and gray wolves, and egg-stealing skuas, Glaucous Gulls, and jaegers.
But fending off predators is just one item on a list of challenges to be overcome on the Arctic tundra. Weather tops the list. For most of the year, the life-giving sun appears only briefly over the southern horizon and shines weakly, and temperatures stay far below zero. At Pond Inlet on Baffin Island, part of the snowy’s breeding range, average temperatures rise above freezing only in three months — June, July, and August. And even then, when the area is bathed in 24-hour sunshine, the mercury never climbs much above 40 degrees F. The average for the year is 5.5.
The Snowy Owl’s large size — it’s the largest of North America’s 18 species of owl — helps the bird deal with the cold, since larger birds can carry more insulation than smaller birds. More important is the owl’s ability to synchronize its breeding with the dramatic change of seasons. Choosing to nest when lengthening periods of sunshine cause temperatures on the tundra to rise, the snowy maximizes its chances of breeding success.
The female lays her eggs in little more than a scratch in the ground less than two feet above soil that has been frozen since the Ice Age, and she alone incubates the eggs. Keeping the clutch warm even in May, when temperatures are still below freezing, she is sustained in her labors by the male, which not only guards the site but brings food to her and, later, her brood.
The owl appears to be an opportunistic hunter, concentrating, especially in winter, on whatever prey happens to be abundant locally. It will attack and kill foxes caught in traps, full-grown chickens and grouse, or ptarmigan downed by a hunter’s shot. It will hunt ducks, grebes, waders, and other birds. It will take advantage of holes in the ice, using its talons to seize fish when they swim near the water’s surface, and it will eat carrion.
“The Eskimo are well acquainted with these birds and with their habits,” A. C. Bent quotes an early explorer as saying. “One man told me he had seen these owls catch the large Arctic hare by planting one foot in the hare’s back and stretching the other foot back and dragging its claws on the snow and ground; at the same time the bird used its wings to hold back, by reversed strokes, until the hare soon became exhausted, when it was easily killed.”
The owl hunts at all hours during summer, and often by doing little more than sitting and waiting. Possessing excellent vision and equally good hearing, it will perch for hours, motionless except for its swiveling head. Alert to any sound or movement, the owl will wait for prey to get close, then strike.
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 Click to enlarge
Adult measurements: About 23 inches (600 mm) and from 3.5 to 6.5 pounds (1,606-2,951 grams). Females are larger than males.
Range: Circumpolar. In North America, breeds in Arctic tundra and Canadian islands (red). Winter range (blue) overlaps with breeding range in yellow regions and extends south of the U.S.-Canadian border. During irruption years, immature males fly as far south as the Gulf Coast.
Habitat: Breeds in the open, treeless Arctic tundra and, far north, near seacoasts. Prefers areas with slight elevations, which are drier than low spots, and from which it can scan the surroundings. Wintering owls choose parking lots, coastlines and other areas that match the tundra’s openness.
Diet: Usually mammals such as rodents and rabbits, but also birds as large as geese, and fish and other aquatic mammals.
Nest: An unlined, uninsulated hollow, scratched out of the bare ground in a spot where wind keeps the snow and moisture from accumulating.
Eggs: Lays 3-11 creamy white eggs, about one every two days, between early May and the end of June.
Incubation Period: 32-33 days.
Young: Newly hatched chicks develop short, white down that is soon replaced with long, dusky-colored down with gray tips. Young leave the nest after about 2-3 weeks but are fed entirely by the parents for another five weeks or longer.
Migration: From December to mid-March, but as early as November and as late as April. Adult females stay closest to breeding grounds. Adult males travel farther, and immature females fly farther still. Young males travel farthest.
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A regular migrant
The mainstay of the snowy’s summer diet is
rodents, and especially the lemming, which tunnels under the tundra in
summer in search of grasses and roots to eat and doesn’t hibernate in
winter. The openings to its burrows are a favorite location for the
snowy’s sit-and-wait hunting technique. Researchers estimate that an
adult Snowy Owl will eat as many as five of the five-inch-long furry
mammals a day, or between 600 to 1,600 lemmings a year, and that two
adults with nine owlets could eat as many as 2,600 lemmings between May
and September alone.
Since the owl obviously exploits the
lemming, and many owls usually appear in southern Canada every fourth
winter, it has been assumed that the Snowy Owl’s famous winter
migrations were linked to periodic, continent-wide crashes in the
lemming population. But recent research indicates that the reasons for
the owl’s wanderings may be more complicated than that.
The
lemmings, for example, aren’t distributed evenly across the continent.
Rather, they occupy tundra patches that vary in size — large in one
area, small in another. What’s more, the population doesn’t just crash.
Instead, lemming numbers fluctuate at different rates at different
latitudes. And most intriguing of all, the majority of the owls that
winter in the northern Great Plains appear to be regular migrants.
Their dispersal is patchy, and their abundance within the patches is
variable, but their winter movements seem to be linked to the local
availability of prey, not a broad population crash.
The Snowy
Owls that show up in eastern and western North America, making news on
Internet listservs and startling and delighting birders as far south as
the Gulf states, are anything but regular migrants, of course. Their
irruptions are as unpredictable as the owl is beautiful.
Exactly what drives them to wander remains to be determined. |
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Tom Jenkins is a freelance writer from Englewood, Colorado.
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