The West Nile virus has been detected in three of 16 ruffed grouse that were found sick or dead and submitted by the public to the Wisconsin Department of Natural Resource for testing from October through December 2018.
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. Ruffed grouse populations are known to rise and fall over a nine- to 11-year cycle, so declines are not unexpected, though the 2017 decline occurred before the cycle would typically predict.
Of these 16 birds, 10 were negative for any viral infection, three were positive for Eastern Equine Encephalitis virus, one was positive for WNV and two were positive for both EEEV and WNV. Of the six birds that tested positive for EEEV or WNV, three showed signs of clinical disease, which may or may not have eventually resulted in death.
These results are preliminary, and 238 hunter-harvested grouse samples remain to be tested from the first year of a three-year study of WNV in ruffed grouse across Wisconsin, Minnesota and Michigan.
Preliminary results for year one of this regional exposure study are tentatively anticipated to be available in mid-2019. Ultimately, the timeline for results will depend on the number of samples submitted by each state and the extent to which follow-up testing is required to differentiate between WNV or other similar viruses.
Anyone who finds a sick or dead ruffed grouse is encouraged to submit its carcass for disease sampling — sick or dead ruffed grouse carcasses can be submitted at any time. Observations can be also reported to local DNR Wildlife Management staff.
In addition to sick or dead submitted samples, DNR staff distributed 500 self-sampling kits to grouse hunters statewide with assistance from the Ruffed Grouse Society and the Wisconsin Conservation Congress as part of a multi-year regional study [PDF] with Minnesota and Michigan.
Both WNV and EEEV are mosquito-borne viruses that can affect humans, horses and certain species of birds. Clinical signs of WNV in birds are indistinguishable from those of EEEV and can include tremors, weakness and loss of coordination. WNV was first detected in the state in 2002 but only now has been detected in ruffed grouse. EEEV is considered a native virus and was first detected in Wisconsin’s grouse population in the late 1950s. This historical information suggests that the likelihood of EEEV having population-level impacts on grouse is low.
State wildlife officials say continued focus on habitat management for ruffed grouse is the best method to mitigate potential disease impacts on the population. Ruffed grouse are a short-lived species with only 30 percent of the average adult population surviving year to year. The Great Lakes region contains some of the most extensive early-successional forest habitat and healthiest ruffed grouse populations in the nation. DNR staff are currently working with partners to develop a long-term management strategy for ruffed grouse in Wisconsin.
For more information on ruffed grouse management and disease sampling, search the DNR website, dnr.wi.gov, for “ruffed grouse management.”