DULUTH — Grouse across the western Great Lakes region are being impacted by West Nile virus carried by mosquitoes, including 29% of grouse tested in Wisconsin, but not all birds that carry the disease are dying.
That was the takeaway message Tuesday, Oct. 22, when wildlife researchers in Minnesota, Michigan and Wisconsin finally released results of samples taken on grouse shot by hunters in 2018. The results were months overdue.
Across the three states, tests were conducted on 720 grouse samples, far fewer than the 1,500 organizers had hoped for. Tests on Minnesota grouse found that 12.5% carried the West Nile virus. Wisconsin grouse showed 29% and Michigan 13%.
In 273 samples from grouse that hunters harvested in Minnesota during 2018, 34 samples had antibodies consistent with West Nile virus exposure that were either confirmed in 10 samples or likely in 24 samples. The Minnesota tests did not find the presence of the virus in any of the ruffed grouse hearts, meaning the birds were not sick when harvested. Some of the Michigan and Wisconsin birds did have the virus in their hearts.
It's good news that some grouse can carry the disease and develop antibodies to overcome it. But it remains unknown how many birds are dying from the virus without being found or how much the virus is keeping grouse populations down.
“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.”
Starting last season and continuing this year, wildlife officials in all three states have been asking hunters to submit freshly-shot grouse samples to test for the virus to see if it may be among the reasons grouse numbers are low. The effort is expected to continue through 2020 in Wisconsin and Michigan. Minnesota will stop with 2019 results, Roy said.
"We are grateful to hunters for taking the time to submit samples from the birds they harvest. This work is only possible with their support, and we appreciate their patience in waiting for test results," said Mark Witecha, Wisconsin DNR upland game ecologist.
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.
There's reason for concern: An earlier Pennsylvania study found West Nile virus was impacting enough grouse that there was a connection between more West Nile virus and lower grouse numbers, especially in areas where grouse habitat wasn't the best. In quality habitat areas — a diverse forest with both young and old aspen and other species — the disease had less impact on grouse.
West Nile virus has been found in 300 species of birds since it was first detected in the U.S. in 1999. The virus was already known to kill crows and blue jays in Minnesota, and the stuff can be transmitted from mosquitoes to humans. Until now it hadn’t been found in grouse in Minnesota.
Several grouse tested in 2018 in Michigan and Wisconsin had already been reported as West Nile positive. Some were emaciated birds that looked bad. Others appeared perfectly healthy.
After the Pennsylvania study showed problems, wildlife managers in the western Great Lakes began to wonder if the recent, sharp downturn in grouse numbers in their states may be related to the virus, leading to the regionwide testing effort starting last fall.
Experts said there may be two reasons why grouse in higher quality habitat fared better against West Nile. Those birds are likely in better physical shape and better able to withstand the virus. Those areas also are better suited to produce more new birds each spring, meaning populations there can bounce back quicker.
"Our continued efforts to provide quality young forest habitat for ruffed grouse is our best strategy to maintain a healthy grouse population that can handle impacts from stressors such as disease or weather," Witecha said.
"Good habitat is our best defense," Roy added, noting some birds like crows and jays are more impacted by West Nile while others, like robins and chickadees, don't seem impacted at all. Grouse seem to fall in the middle.
Ben Jones, CEO of the Ruffed Grouse Society, said Pennsylvania has more than six years of West Nile data that show similar results.
"What I think we are finding out, as we get more science on this virus, is that some years will be worse than others, but that it's always out there and it's going to impact the population at some level," said Jones. "But it's also clear that where we have a good mix of habitat, grouse can be more resilient ... and that this isn't going to be the end of grouse."
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 meat from infected birds. Some bird species recover quickly and become tolerant to the virus while others, such as blue jays and crows, suffer high mortality rates.
More information about ruffed grouse management can be found on the Minnesota DNR website at mndnr.gov/hunting/grouse.
Hunters asked to help in West Nile virus effort
Ruffed grouse hunters in Wisconsin, Minnesota and Michigan can assist wildlife health officials again this autumn as part of a multi-year study monitoring for West Nile virus in ruffed grouse. As they did in 2018, the departments of natural resources in each state this year are asking hunters to submit samples from their harvested ruffed grouse. Each state will give out about 500 sample kits that hunters can pick up that include detailed instructions and the supplies needed to take samples — feathers, blood and the heart — from freshly harvested grouse to submit for review to see if the bird has been exposed to the mosquito-borne virus.
The kits are available at DNR wildlife offices across the grouse range in each state. Hunters will be provided test results via email. However, testing of samples will not begin until after the grouse season has closed, and final results will not be available for several months after the close of the season.
In addition to collecting samples from harvested ruffed grouse, the Wisconsin DNR is asking the public to report any sick or dead grouse observed while out in the field. Anyone who sees a ruffed grouse that appears sick or emaciated, or who finds a freshly dead grouse should take note of the location and promptly call a DNR wildlife biologist for possible testing and to help track reports statewide.