News Release

West Nile virus in ruffed grouse: Test results are in

October 22, 2019


Test results are in from the first year of a multi-state study on West Nile virus in ruffed grouse in Minnesota, Michigan and Wisconsin. These first-year results are showing that, while the virus is present in the region, exposed grouse can survive. 

In 273 samples from grouse that hunters harvested in Minnesota during 2018, 34 samples (12.5 percent) had antibodies consistent with West Nile virus exposure that were either confirmed in 10 samples (3.7 percent) or likely in 24 samples (8.8 percent). The tests did not find the presence of virus in any of the ruffed grouse hearts, meaning the birds were not sick when harvested.

In Wisconsin, West Nile virus exposure was detected in 68  of 235 (29 percent) ruffed grouse blood samples with exposure to the virus either confirmed in 44 (19 percent) or likely in 24 (10 percent), and two grouse had virus present in their hearts. In Michigan, West Nile virus exposure was detected in 28 of 213 (13 percent) ruffed grouse blood samples with exposure to the virus either confirmed in nine (4 percent) or likely in 19 (9 percent), with four having virus present in their hearts.

“The study tells us that some birds that have been exposed to West Nile virus are surviving – both juvenile and adults – and they are not sick when harvested in the fall,” said Charlotte Roy, grouse project leader with the Minnesota Department of Natural Resources. “But this study does not tell us about birds that may have died from the disease over the summer.”

Research in other states points to good grouse habitat as one factor that can produce birds in better condition and better able to survive stressors like West Nile virus.

The DNR had asked grouse hunters to collect two types of samples to help determine if the birds were exposed to the virus: a blood sample to determine if the grouse had developed an immune response to the virus, and the heart to look for traces of viral genetic material. As in humans, ruffed grouse can build up antibodies in an immune response to viruses they encounter. Even when the body fights off an illness, these antibodies are left behind in the blood.

Hunters who submitted samples in 2018 will be mailed a letter this fall notifying them of the test results of the birds they submitted.

“Thank you to all hunters who contributed samples last year, as well as hunters who are submitting samples this season,” Roy said.

Sample collection is continuing during the 2019 grouse hunting season. Ruffed grouse hunters can voluntarily submit samples if they are willing to collect blood on filter paper strips within 30 minutes of harvest, hearts, and a few feathers for sex and age determination, and are willing to provide harvest location information.

Sample collection kits have been available for pickup at DNR area wildlife offices within the ruffed grouse range since Labor Day on a first-come first-serve basis. Due to strong interest by hunters, many offices are already out of kits, so hunters should call ahead before stopping. 

This year, the Ruffed Grouse Society is offering a shotgun and Pineridge Grouse Camp is offering a guided hunt as prizes in a drawing for participating hunters who submit samples correctly.

West Nile virus has been present in Minnesota since the early 2000s, but interest in effects on ruffed grouse increased following a study in Pennsylvania documenting relationships between habitat quality, populations and virus exposure. Some bird species recover quickly and become tolerant to the virus while others, such as blue jays and crows, suffer higher rates of mortality.

West Nile virus is carried by infected mosquitoes. Not all people or animals bitten by an infected mosquito will contract West Nile virus. There have been no documented cases of people contracting West Nile virus from consuming properly cooked meat.

More information about ruffed grouse hunting and sampling is available on the DNR grouse hunting page.