RED WING, MINN. — From a blue sky here one day last week appeared a helicopter flying as most do, advancing with a thump, thump, thump of its rotors, presumably transporting a sick or injured person from one hospital to another, or perhaps toting a television news crew.

Instead, as the chopper flew closer to the ground before hovering briefly, then landing, an emblem on its front door designated it as one of a handful of aircraft belonging to the Department of Natural Resources.

This particular helicopter, an OH-58C that from a distance resembles a Bell Jet Ranger, was purchased for a song a couple of decades back after it was discarded by the military.

At its controls was DNR standby pilot Brad Maas of Brainerd, where the helicopter is stationed. With him were wildlife supervisor Dave Pauly, whose home district is the Cambridge area, and DNR deer researcher Brian Haroldson of Madelia.

Until a couple of weeks ago, none of the three imagined that on this midwinter's day they would be in southeast Minnesota.

But their plans -- along with those of a few score other DNR employees -- changed when a deer killed by an archer Nov. 28 about 3 miles from the town of Pine Island, Minn., was discovered to be infected with chronic wasting disease (CWD).

The doe was the first wild deer in the state known to be afflicted with CWD, and the DNR in the days since has worked overtime developing a response. Key components have included aerial surveys of deer in the area, following which -- beginning this weekend -- a representative sample of that whitetail population will be killed.

The DNR hopes about 900 deer in all will be felled in coming weeks, before the deer disperse in early March. The plan is for 500 animals to come from a core area within a 5-mile radius of the spot where the infected deer was shot, with the remaining 400 deer killed in a larger, 10-mile-radius area.

"It's a significant number of deer, but with respect to the total number of deer on the landscape, it's not a lot," said DNR big game coordinator Lou Cornicelli.

The DNR estimates about 6,500 deer inhabit the 10-mile-radius area.

Because all property in the CWD zone is privately owned, landowners or their designees will be given first shots at the deer, literally.

Ten tags will be awarded to each property owner initially, with more added as needed, Cornicelli said.

Wildlife officials want harvested deer to come from diverse parts of the 10-mile-radius CWD zone.

"Our hope is that we can get the majority of the needed sample with landowner shooting," Cornicelli said. "Our goal is to determine the level of infection in the local deer population and to remove additional potentially infected animals."

Killing some of the area's deer is the only way to determine whether the disease has spread to other deer, as it has in southern Wisconsin, and if so, how widespread it might be, Cornicelli said.

Landowners aren't obligated to shoot deer on their property. Nor are they required to allow others on their land to kill deer. The DNR is seeking widespread cooperation, however, so it can accurately assess the threat CWD poses to Minnesota's wild deer population, which is estimated at more than 1 million animals.

If landowners agree to allow deer killing on their property but don't want to do it themselves, U.S. Department of Agriculture sharpshooters might be employed.

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Last week, Maas, Haroldson and Pauly crisscrossed the 5-mile-radius CWD core area deliberately in the DNR helicopter, determining, in the end, that close to 1,900 deer winter there.

"We already had a DNR fixed-wing aircraft survey the larger [10-mile-radius] area," Pauly said Wednesday. "But because of the speed that plane has to fly, its survey is capable of showing only where concentrations of deer are. With the helicopter, we can make much more detailed counts."

Anyone who doubts the DNR's ability to accurately count deer -- or for that matter other big game, such as moose or elk -- need only spend a short time with Maas, Pauly and Haroldson.

Using software specially developed by Haroldson and others in the DNR, they're able to accurately record not only deer in the area but any carcasses they come upon, along with food plots or other feeding sites.

"And what we saw is that there's a lot of deer feeding going on in the area," Cornicelli said. He said a DNR-imposed feeding ban will begin later this month in Olmsted, Wabasha, Goodhue and Dodge counties.

CWD is always fatal to deer, elk and moose, and while no Minnesota moose have been affected, the disease has been found in captive elk here, beginning in 2002.

CWD is not believed to affect humans, though variations of the disease do.

In the past eight years, the DNR has tested more than 32,000 hunter-killed or road-killed deer, 60 elk and 90 moose for CWD. The archer-killed deer felled in November has been the only wild animal found with CWD.

In the Pine Island CWD case, captive elk are prime suspects. Two years ago, four elk in a captive herd near that town were found to be infected, and the herd was "depopulated" -- killed in its entirety.

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In the helicopter last week, Haroldson rode up front, alongside pilot Maas. Pauly, who has participated in many similar aerial surveys, sat in the back, eyes peeled for whitetails.

All wore protective helmets, and the chopper maintained an altitude of about 200 feet.

Key to the survey was a detailed map that divided the 5-mile-radius CWD zone into 101 square-mile sections. The map's center -- section 53 -- was where the CWD-infected deer was killed.

Maas used an electronic version of the map for navigation, and the helicopter's route was recorded on it. Similarly, the map -- many versions of it, in fact -- was loaded into a laptop computer Haroldson held.

Every time he and Pauly saw deer, Haroldson touched the laptop's screen, using a stylus and recording the animals' exact locations.

Deer numbers also were recorded, and the direction they were moving, if any.

River draws and woodlots in particular received close looks, whereas farm fields that could more easily be assessed from afar were passed over relatively quickly.

In their first two days of flying, Haroldson and Pauly counted 840 deer in 60 sections, or 14 animals per square mile. By the time they completed their survey Thursday, the deer density had increased.

"We developed this software to do deer population surveys in the agriculture and transition parts of the state," Haroldson said. "We do different deer permit areas every year to test and improve our population models."

How much does all of this cost -- not only for the aircraft, but for DNR personnel, fuel and other expenses?

As much as $400,000 by one estimate. And the Legislature will be asked to help foot the bill, which so far is being paid by hunting-license fees.

Whoever pays, eradicating CWD from the state's deer herd, if possible, is critical, Cornicelli said.

"You can't look at this disease as a one-, two-, five- or even 10-year event," he said. "You do it now, and maybe you won't have to do it over again 100 years from now."

Dennis Anderson • danderson@startribune.com