I happened to catch part of the NBC Nightly News earlier in the week. The newscaster prepped the after-commercial-break segment with reference to an “invasion” in the state of Minnesota. I knew immediately what it was about: the mass migration of thousands of great gray owls from their territories in Canada, as well as hundreds of other rarely seen northern owls such as the northern hawk owl and the boreal owl.

Great gray owls do breed in the western U.S., but the bulk of their population resides year-round in northern Canada and Alaska. They also breed in Minnesota but are hard to spot in some years; no wonder an incursion of almost 2,000 of these large, imposing owls caught people’s attention.

The NBC reporter interviewed local birding expert and enthusiast Sharon Stiteler, who demonstrated different owl calls and commented on the invasion. The correspondent then mentioned Stiteler’s Web site: www.birdchick.com – so of course I checked it out.

“Great gray owls are practically dripping from the trees in St. Louis County,” she writes. “If you are remotely interested in owls you must come here. If you have always thought that you wanted to visit this area, this is the year to do it. We always have a few in the area, but nothing like this. Do what you have to do (take a sick day, borrow money), but it’s worth it to see so many owls in one day.”

An unusual event such as this occurs when the prey base of these owls crashes, sending the birds out of their usual range in search of food. While this may be great for birders, it is obviously not great for the owls; in many cases, the birds may be on the brink of starvation and severely stressed.

The increased contact between owls and people has also taken its toll: more than 250 owls have been struck and killed by motor vehicles as they swooped low over roadways while hunting, according to the NBC report. Injured survivors are taken to the University of Minnesota’s Raptor Center to recuperate.

At 27 inches, the great gray owl is our largest North American owl in terms of length. Another northern owl, the snowy owl, beats the great gray in weight. It is 4 pounds, as compared to the great gray’s 2.4 pounds).

With its large facial discs, piercing yellow eyes, and regal stance, the great gray has become a haunting symbol of the northern wilderness. Its imposing stature is somewhat misleading, however. Although reported to be fierce and aggressive in defense of its young, it rarely hunts anything larger than its favorite prey, the meadow vole. This small mammal spends a comfortable winter tunneling under the snow, but it cannot escape the keen hearing of the great gray. Even in deep snow, the small sounds made by its movements are detected by the owl.

Upon hearing the vole, the owl dives headfirst into the snow with its talons drawn up under its chin, catching its prey with deadly accuracy. A light, powdery snow pack is no prerequisite for this feat; researchers have reported great grays can punch through snow crust thick enough to support a 180-pound man.

Invasions such as the one occurring in Minnesota (and Wisconsin, as well as possibly other states and southern Canada) occur in cycles. The last recorded invasion of great grays occurred during the winter of 1991-92. At that time, 196 great gray owls were recorded in Minnesota, 234 were recorded in Ontario, and less than five were recorded in New England.

This winter did bring at least one great gray owl to Maine. The bird was seen only briefly and photographed in the town of Gray (how appropriate!) on Jan. 23.

These birds will most likely be seen near bogs, marshes, or other open areas surrounded by low perches. Be on the lookout…. You just may find one, especially in an invasion year.

NEWS bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net