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An invasion of owls

Why the snowy birds have descended from the Arctic to southern Manitoba isn’t thoroughly understood

Southern Manitoba has been invaded by snowy owls travelling far from their breeding ground north of the Arctic Circle.

The owls began arriving as early as October. This phenomenon, called an “irruption,” happens at irregular intervals, usually every four or five years. Occasionally they happen two years in a row.

Occasionally a “mega-irruption” may occur, in which even greater numbers of owls migrate much farther south, perhaps as far down as Florida. The winter of 2013 to 2014 had the largest irruption in Eastern Canada and the northeast U.S. in over a century.

The reason for irruptions is not completely understood. It used to be assumed that the owls came south because of a lack of food in the North, but the latest research suggests just the opposite. A year with large numbers of lemmings, voles and ptarmigan means there is an abundance of food for snowy owls during the summer. This also means more owls congregate in such areas and more nesting females successfully hatch and raise more young.

When food is scarce they may lay only three to five eggs. When food is abundant they may lay twice that number. Many of the migrants appear to be young birds migrating after a good summer. It appears that irruptions are only occasionally caused by a scarcity of food.

Another theory is that early and deep snows in the Arctic cause a greater movement south.

Male and female snowy owls look quite different. The females are larger and weigh up to three kilograms. They’re the biggest North American owls by weight. The females are heavily barred with black, a protective feature to help camouflage them when they are nesting on the ground in summer. Males are usually much lighter, becoming almost pure white as they get older. Juvenile owls usually also have some dark colouring.

Photo: Donna Gamache

Snowy owls, which come from the treeless tundra of the North, tend to avoid trees when they come south.

Most often they are sighted on large open fields and pastures, or along power lines, perched on the poles. Because they come from a place that may have almost continuous light in summer and almost continuous darkness in winter, they have adapted to be able to hunt at either time.

This winter, so far, looks to be a good one for Manitobans to see these beautiful birds. Keen birders often drive country roads watching and photographing them. Just remember not to approach too close, in order to avoid causing the owls stress.

If you’re interested in learning more about snowy owls, or following their paths of migration, check out Project SNOWstorm at projectsnowstorm.org.

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