Northern harriers are aerobatic hunters

You should not text while driving. You should not use your cellphone while driving. Nor should you attempt to photograph birds on the wing while driving.

Asking your wife to steer from the passenger seat while you control gas, brake and camera is only a slightly better idea. Telephoto lenses tend toward heavy and they're often unstable. A moving car on a gravel road makes the task very iffy.

Harriers, however, are such beautiful birds, with such potential for cooperation.

"Just steer for another minute. It's heading our way."

"It" is a sleek gray bird trimmed in black and white, a Northern harrier, known as a marsh hawk for many years. It is tacking into the wind over this piece of prairie, sliding and gliding, tipping into sudden turns that reverse its direction as it spots prey.

It is hunting almost right alongside the road.

We were on another road trip, this time to open grass and marshland to the west. Perfect for harriers and photographers, all on the hunt.

Made for the hunt

Harriers let you watch their slow, methodical work. Both sexes hunt from just above the ground, raking prairie grass or marsh with their eyes as they work upwind, heads tipped to the tangle below.

Hawks, like all bird families, have divided the earth into pieces assigned to particular species, hunting in particular ways for particular prey.

Harriers own hayfields and marshes and grass, and the small rodents that live there.

Harriers have a facial ruff, much like owls. It helps focus small sounds from the ground that guide the bird to prey. Vision is important, too. (Most raptors could read a newspaper at 50 yards.)

The harrier has another hunting advantage: It can see ultraviolet light, a trait common to many bird species.

Human eyes have three sets of cones used for color perception — red, blue and green. Birds have those, plus cones for ultraviolet light.

The urine of many rodents, prairie voles and mice for instance, is sensitive to the ultraviolet spectrum. Squirts of urine glow brightly in harrier eyes. Just follow the dotted line.

Where to find them

Harriers are Minnesota birds, breeding in most parts of the state. Unfortunately, they are hard to find where marshes have been destroyed, and grassland turned to cropland or housing developments.

If you want to find them, go to northwestern Minnesota. Go to Crex Meadows at Grantsburg, Wis. Go west of the Missouri River.

A few years ago we drove to a southern Minnesota marsh lush with long grass. Short-eared owls had been reported to be hunting there. And they were, casing the field much as the hawk would do. A harrier appeared, but quickly received the bum's rush from the owl.

I stepped into the grass to move closer. I could watch the voles and mice jump out of my way. Harriers — and owls — will look for such fields, for the polka-dot pattern of rodent piss. Such a field would make a fine nesting site.

Male harriers could have one mate, and might have five. Food supply determines the relationships. Their nest is on the ground. The female, larger than her partner and brown, also will hunt once eggs hatch. (Both sexes can be recognized by a bright white rump patch.)

The other way to photograph these birds is to speed up, get ahead of the bird, slam on the brakes, and hope for the best. Sometimes the bird slides in your direction. Sometimes it doesn't.

In all cases, though, this acrobat is worth the search, worth the protests coming from the seat beside you.

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at www.startribune.com/wingnut.