Wisconsin's first confirmed cases of West Nile virus in ruffed grouse were reported Tuesday by the state Department of Natural Resources.

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The DNR said that West Nile was confirmed in three of 16 grouse tested so far. The DNR said the results are still preliminary because another 238 grouse samples remain to be tested.

The agency is testing both sickly grouse that were turned in to wildlife officials and grouse blood samples submitted by hunter volunteers in the field.

Wildlife researchers are concerned that West Nile virus may be one factor leading to an unusually rapid and steep decline in grouse numbers in recent years. Researchers in Wisconsin, Minnesota and Michigan this winter are testing hundreds of grouse samples obtained by hunters from birds shot last fall to see how prevalent the disease is in the popular game bird.

Michigan already had five positive West Nile hits in 2018 and officials in Pennsylvania say West Nile may already be a big enough factor there to spur grouse population declines, especially in areas where the bird is already stressed by poor habitat conditions.

After the Pennsylvania study showed problems, wildlife managers in Minnesota, Wisconsin and Michigan began to wonder if the recent, sharp downturn in grouse numbers in the Midwest may be related to the virus, leading to the region-wide testing effort last fall. Minnesota grouse drumming was down 29 percent in 2018 from 2017.

Charlotte Roy, grouse project leader for the Minnesota DNR, said her agency has not yet received any results from Minnesota grouse tested for West Nile. She expects the first results by March.

The Wisconsin Natural Resources Board last fall moved to chop a month off the state's grouse hunting season because of concerns over a declining population and the potential impact of West Nile virus on the bird.

The Wisconsin DNR said it's too soon to say West Nile is an issue for the state's overall grouse population.

"At this time, there is no evidence to confirm that West Nile virus or any other factor is having population-level impacts on ruffed grouse in Wisconsin," the agency said Tuesday in announcing the results.

Ruffed grouse populations are known to rise and fall over a roughly 10-year cycle, so declines are not unexpected, the DNR notes, although "the 2017 decline occurred before the cycle would typically predict."

In addition to the West Nile detected, researchers found Eastern Equine Encephalitis in five of the birds, including two of those that also had West Nile.

West Nile has been detected in other birds in Wisconsin and Minnesota since the early 2000s and is believed to have caused a decline in some crow and blue jay populations.