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One of two recently documented snowy owls found north of Fargo. The heavy barring indicates this is an immature bird. Keith Corliss / Forum Communications Co.

Flight Lines: Sharp snowy owl contrast between last two winters

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flight lines Fargo, 58102
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We are under an invasion. Unlike Orson Welles' 1938 radio adaptation of H. G. Wells' novel, War of the Worlds, this one is real and it's coming from the north. There is little we can do to stop it, but like the harmless romp Welles's program turned out to be, this current invasion is relatively harmless, too. That is unless you happen to be a small furbearer, a primary food source for snowy owls (Nyctea scandiaca).

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The movement of a bird species following the breeding season into areas beyond their normal range is more properly labeled an irruption. Several different words, however, are fairly interchangeable and used by birders to describe this phenomenon, including invasion, influx, or incursion. Whatever a person labels it, it means the same thing.

The current snowy owl irruption started rather quietly a few weeks ago, when scattered reports began to come in from the northern part of North Dakota. That alone was noteworthy, due to the extreme lack of snowy owl sightings all last winter. This season would be different. By late November, two birds were noted just north of Hector International Airport in Fargo. That same week, someone created an interactive Google map of the U.S. showing snowy owl appearances throughout the country, and the birds were documented as far south as Kansas. Surely something unusual was (and is) taking place.

Snowy owls are the largest (in terms of body mass) of the North American owls, but usually go about their business unseen and undisturbed in the windswept openness of Arctic tundra. The species is circumpolar, meaning the Russians and Northern Europeans are familiar with this bird, too (the species name, scandiaca, refers to Scandinavia where the bird was first observed by science).

The birds range in appearance from a nearly pure white (adult males) to heavily darkly-barred individuals (immatures) and everything in between. Females will typically retain some dark barring even into adulthood. Offsetting these fairly monochromatic features are yellow eyes.

Not surprising for a creature of extreme climate, snowy owls possess an exceptionally dense and luxurious plumage. The toes are heavily feathered and the talons and beak remain almost hidden from view due to feather density.

So tied are the birds to treeless tundra, you will rarely if ever see one perched in a tree. Of all the snowy owls I've seen in my life, there was only a single instance where one was on a tree and even that was a broken off stump. Instead, the birds regularly perch on power poles, fence posts, and commonly, the ground.

From conspicuous perches the birds hunt regularly during the day in contrast to most of our owls. Prey species include virtually anything as big as or smaller than itself, such as lemmings, snowshoe hares, voles, prairie dogs, birds, and even fish. But during the breeding season, it's all about lemmings, with which the lives of snowy owls are inexorably linked; linked so closely that the owls only breed successfully during peak lemming years (every three to five). Indeed, without this abundant and readily obtained food supply, the birds simply cannot fledge young.

I found a compelling numerical illustration of this intricate relationship in one source stating that, during good lemming years there might be 20,000 snowy owls on Banks Island, a large but remote piece of land in the Canadian Arctic Archipelago. In contrast, there are perhaps 2,000 during low lemming years. That's a factor of 10. And so we come to the current irruption. Some sources tell us snowy owls are coming south this winter due to a crash in lemming numbers, but that might be too simplistic. Some birds surely move south every year but in limited numbers. Yet the ones being seen this season appear to be mostly immature, which would lend evidence to the theory the birds enjoyed a robust nesting season and the young birds are simply dispersing.

Whatever the reasons for the large influx of snowy owls, it's amazing to ponder that many of them stay the winter on their breeding grounds, somehow surviving an Arctic winter with little heat and even less light. To the delight of those unwilling to venture any farther north at the moment, though, it's refreshing to be able to view some of the more itinerant ones close at hand.

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