Gyrfalcons are casual winter visitors, with a small outpost in South Dakota.

It’s the year 1200. You’re invited to a birthday party for a Scandinavian king.

Two things to consider. First, what are you going to wear? Second, what do you give a guy who has everything?

A white gyrfalcon.

He’ll love it. It’s written that such a bird was worth its weight in gold.

Medieval royalty was big on falcons. The birds were used for hunting, as they are today. Falconry has been a sport for thousands of years. Falcons as gifts for royalty date to 2200 B.C. in China.

The kind of falcon you were allowed to own in England in medieval times depended on social position. Gyrfalcons were reserved for kings.

Earls could fly peregrine falcons, a yeoman (landowner) could have a goshawk. Our sharp-shinned species, called sparrowhawk in England, was reserved for priests. Servants could have kestrels.

Theft of a trained raptor was at times a capital crime in England.

White gyrs most often came from Iceland. They were captured as trade goods.

Gyrs, largest of the falcon family, are found in all Arctic regions, worldwide. Iceland was convenient for Europeans.

In North America the birds breed in the high Arctic, ranging in winter as far south as Montana, the Dakotas and here.

In Minnesota they are classified as “casual,” sporadic and irregular. They are most often seen in the Arrowhead region. Most sightings are from Duluth-Superior (where you also find most of the birders).

My first gyr was perched atop a grain elevator near the Duluth harbor. It was a brownish bird, most likely a juvenile, a yearling. Adults are gray, black or white.

My second gyr was gray, near Nome, Alaska, beside its nest on a cliff along a road leading out of that outpost.

I say nest because I faintly recall sticks, but the excitement of the sighting might have blurred my memory.

If the gyr had a nest it was built by another raptor, confiscated by the falcon. Gyrs would be content with scraping the cliff surface smooth, then laying eggs. They don’t build nests. (Would a king build his own castle?)

My third gyr is the one I remember best. It was in South Dakota, on the grasslands east of Pierre. The sighting was unusual because I actually was there to look for that species, long as the odds were.

In the National Geographic book “Complete Birds of North America,” the map showing gyrfalcons’ winter range is colored light blue for much of western and central Canada. There is that shallow dip into the U.S. And then, there’s a drop of blue in the middle of South Dakota — the Fort Pierre grasslands.

The grassland has a gentle roll to unbroken horizon. It is cut with infrequent gravel roads. I drove up a small hill to find my gyr perched on a fence pole, a majestic bird, fit for a king.

I wanted my trophy, a photo. I watched until nerves got the better of me, then snapped six quick frames from the van window just before the bird flew, low and away on strong wingbeats.

It was there to hunt pheasants and prairie grouse, menu substitutes for the rock and willow ptarmigan it eats at home.

I also saw golden and bald eagles on that trip, and prairie falcons, rough-legged, red-tailed, and ferruginous hawks. They were — are — also there for the pheasants and prairie grouse.

South Dakota’s e-mail bird alert, similar to ours, notes gyrs, three so far this winter. One of them was white. A gyr was mentioned on the Dakota list as recently as Jan. 4.

That grassland is my favorite birding destination. It’s easy to call it empty. But it’s filled with surprise.