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Sunday, November 26, 2000

By Scott Shalaway

A few days ago, two hours before dawn, I heard a late fall sound that assured me winter is almost upon us and spring, though distant, will return. A great horned owl hooted in the hollow below the house. I answered, and we talked back and forth for five minutes. Then another owl entered the conversation. It seemed positioned near the top of the ridge, a good 200 yards from the first singer. I took my leave and let the courtship proceed.

A snowy owl rests on the roof of Laval House on Duquesne University campus, a sure sign winter is right around the corner. (Andy Starnes, Post-Gazette)

Birders set their ecological clocks to the hoots of great horned owls. They court from November through January. By the end of the year's first month, the female lays two or three eggs in an old red-tailed hawk or crow's nest. Or if a large tree cavity is available, she may seek its shelter. In any case, great horned owls are the year's first nesters, and active nests rarely escape a snowfall or two.

This year a different owl has captured the attention of birders in New Jersey and Pennsylvania, and I suspect it will appear widely across the midwest and mid-Atlantic states. Snowy owls are back.

Snowy owls often appear throughout the midwest and northeast, but their occurrence is unpredictable. The winter movements of these large white owls has long been attributed to crashes in arctic lemming populations, but the more we learn about the snowy owl/lemming predator/prey relationship, the less clear it becomes.

Lemmings are small mouse-like rodents and the principal prey of snowy owls. Despite their order on the food chain, snowy owls actually benefit lemmings. Snowies concentrate their activities where lemming are most abundant and therefore frequently fertilize the surrounding soil. Vegetation prospers on thusly fertilized arctic soils and provides critical food and cover for lemmings. So even a predator that eats as many as 1,600 prey per year can benefit that prey.

Because lemming populations peak at four-year intervals, it seems reasonable that owls might wander south when lemming populations crash. But snowy owls also eat hares, other rodents, grouse, songbirds, and even small waterfowl. Furthermore, lemmings are not evenly distributed across the arctic tundra. Their distribution is patchy, and their population cycles are not completely synchronous. So even when lemmings disappear in one area, there's a good chance there are many more within just a few hundred miles.

And yet snowy owls head south more often than expected. More years than not, snowy owls make winter appearances in Missouri, Kentucky, Ohio, Maryland, New Jersey, and states north. Prey that peaks every four years hardly seems a good explanation for the owls' frequent movements. Perhaps their winter wanderings are more predictable than once thought and driven by a reliable supply of winter prey, wherever that may be. Or perhaps, as some observations suggest, it is the young of the year that come south, chased off by dominant older birds that control the arctic food supply. Snowfall and extreme winter temperatures might also help explain the winter movement of snowy owls.

Regardless the reason, when snowy owls visit temperate areas, people notice. Newspaper coverage is common, and sometimes an ambitious television station ventures afield for a nature story.

Snowy owls stand about two feet tall and have a wingspan of more than four feet. Older males are mostly white; first year birds are heavily marked with black bars, and adult females show some black barring. All have yellow eyes and white faces and are diurnal.

When snowy owls invade temperate zones, they hunt open tundra-like areas -- grasslands, hayfields, and airports. Look for them perched on fence posts, power line poles, and even the roofs of buildings.

In April snowy owls return to the arctic where they nest on the ground. There, nesting success is clearly related to food availability. When lemming populations are high, females lay as many as 13 eggs. When lemming numbers are low, they lay as few as three eggs, or may even forego nesting completely.

So keep your eyes and ears open. Tis the season to see snowy owls by day and hear great horned owls at night.

Send questions and comments to Dr. Scott Shalaway, R.D. 5, Cameron, WV 26033 or via e-mail to sshalaway@aol.com, and catch Scott on the radio every Saturday afternoon from 3 to 4 on 1360 WPTT.