Survey Finds Reduction in Deer Population in CWD Zone

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Recent aerial surveys indicate that hunting has reduced the white-tailed deer population by about 10 percent in the zone state officials have established to eradicate chronic wasting disease from Wisconsin, with about a 20 percent reduction in the core area where the disease is most prevalent.

The Department of Natural Resources has conducted aerial surveys the past two winters to determine the deer population in the chronic wasting disease eradication zone (DEZ), which encompasses parts of Sauk, Dane, and Iowa counties in south central Wisconsin.

“We are pleased with the continued progress made in the disease eradication zone at reducing the size of the deer herd in order to control CWD. We are grateful to the landowners and hunters whose efforts have helped reduce the herd this far. However, in order to continue on the track of beating this disease as quickly as possible, we would have liked to have seen more deer taken off the landscape last hunting season,” said Tom Hauge, director of wildlife management for the state Department of Natural Resources.

The size of the DEZ increased from 411 square miles to 964 square miles for the 2003 hunting season. Based on the number of deer seen from the air within the 964 square miles, the population is estimated at about 21,000 deer or about 35 deer per square mile of deer habitat. This estimate cannot be directly compared to 2002-03 survey data because of the change in the size of the DEZ.

In order to estimate a percent reduction in the herd size, the same 411 square mile disease eradication zone area surveyed last year had to be used this year. By comparing the estimated population this winter in the 411 square mile area to the population estimated in the same area last winter, an approximate 10 percent reduction in herd size was determined.

“Reducing the deer herd is tough work. Expecting to see drastic reductions in two years is very optimistic. A 10 percent reduction, with a 20 percent reduction in the area of highest infection, is a step in the right direction,” Hauge said. “However, there is a lot more work that needs to be done if the population is going to be reduced to a goal of less than five deer per square mile.

“Herd reduction in the DEZ is absolutely dependent on landowner and hunter participation. The department will be examining ways to increase landowner and hunter participation for next season. The department will also be looking into ways that it can step up its own herd reduction activities in this area as well,” Hauge said.

For the past two years, the DNR has used aerial surveys to estimate deer population size and trends in the original DEZ. Aerial surveys are used instead of the traditional Sex-Age-Kill (SAK) method, which relies on buck harvest numbers. It is unknown what effect the unlimited earn-a-buck season in the DEZ has on the buck harvest rate, so the SAK method cannot be used.

Aerial surveys within the DEZ are done by helicopter in the winter when there is enough snow to cover rocks and stumps, making deer more observable on the landscape. The amount of snow cover, amount and type of vegetation, light conditions, aircraft type, flight speed, elevation and more, are all factors affecting the number of deer that can be observed.

“Snow conditions and lighting made for good survey conditions this year,” said Robert Rolley, DNR wildlife population ecologist. “But no matter how good the conditions are, a major limitation of aerial surveys is that you rarely see all the deer that are present.”

Rolley estimates that about 80 percent of the deer were observed this year.

“Obtaining accurate and precise estimates of the size of deer populations is not easy by any method. While aerial surveys are our best available method for monitoring deer populations in CWD zones, we are still learning about these survey techniques,” Rolley said.

The DNR will be holding open house meetings between March 16 and 18 in south central and southeastern Wisconsin to discuss population estimates, CWD management and the proposed changes to CWD rules. Public hearings will immediately follow the meetings. CWD meeting and hearing times and locations are on the DNR Web site.