With drumming surveys dropping and concerns about ruffed grouse populations, questions were raised as to what impact west nile virus, found in Wisconsin in recent years, may have to do with that decline. Recently, the first year results of the three-year study were released.
The results show that, of the 235 hunter harvested samples tested, 68 of those, or 29%, had antibodies to West Nile Virus (WNV) either confirmed, which was the case in 44 of those samples, or likely, which was the case in 24 of those samples. Viral genetic material, the abstract stated, was found in two heart samples, which equates to approximately 0.9%. While the study showed ruffed grouse has been exposed to WNV, it also showed they had the ability to develop antibodies to the virus and survive that exposure.
Exposure varies annually, they said. It can be based on not only prevalence of the virus, but also weather conditions and the prevalence of mosquitos. While the report stated the study would not necessarily be able to draw conclusions regarding mortality of ruffed grouse due to exposure to the virus, it would provide a better idea of the distribution and prevalence of WNV on the landscape in Wisconsin. More research would need to be done revolving around free ranging ruffed grouse populations to truly evaluate response of the species to exposure.
In 2017, hunters reported flushing fewer birds than was expected when compared with the brood observations in 2016, not only in Wisconsin, but in Michigan and Minnesota as well. Spring drumming surveys in 2018 provided further cause for concern, as those numbers unexpectedly declined.
Research in Pennsylvania, which was ongoing in the same time frame, noted the presence of WNV had coincided with ruffed grouse declines there as well. Coupled with loss of habitat and forest maturation, it was likely a compounding effect. With this in mind, the Wisconsin Department of Natural Resources (DNR) entered into a joint effort with Michigan and Minnesota in an attempt to determine what effect WNV may be having on ruffed grouse populations in the upper Midwest. The feeling was this cooperative effort would afford researchers a more comprehensive view of the exposure across the region.
Four primary objectives were listed in the study:
• Assess the feasibility of utilizing hunter-harvested ruffed grouse to obtain biological samples from harvested birds for disease screening and collecting relevant metadata,
• Determine the prevalence of exposure to WNV in ruffed grouse populations and if there is significant change by year in Wisconsin,
• Evaluate if samples can be collected in sufficient numbers to assess prevalence across different regions of the state, and
• Examine submitted samples for evidence of clinical disease associated with WNV infection.
The goal of year one of the study was to distribute 500 test kits for self-sampling by hunters. Priority regions included areas in northern and central Wisconsin. A complete data sheet was included with each test kit for the hunter to record pertinent information such as harvest location, body condition of the bird, and age and sex. All samples would then be sent to the DNR Science Operations center in Madison.
From there, samples were sent to the Southeastern Cooperative Disease Study (SCWDS) to be tested for the virus. All three states sent their samples to the SCWDS, where two forms of testing were used. Both blood samples and heart samples were tested.
Of the 235 tests from Wisconsin, birds were tested from 20 counties. From those studies, the 68 with antibodies present indicated the individual was exposed to WNV but had developed an immune response. Three ruffed grouse heart samples from Wisconsin tested positive for Easter equine encephalitis (EEV), which is similar to WNV. EEV was first detected in Wisconsin’s ruffed grouse population in the 50s, when 50% of ruffed grouse sampled tested positive for antibodies of the virus.
Michigan submitted 213 samples, of which 28, or 13% showed exposure to the virus. Viral genetic material was found in four hearts that were sampled.
Minnesota submitted 273 samples. WNV antibodies were detected in 34, or 12%, of those samples. No viral genetic material was found in heart samples from Minnesota. Monitoring effort
Findings so far, the report stated, have shown individual ruffed grouse, while they have been exposed to WNV, are capable of developing an immune response to the disease. This monitoring study, it said, will provide researchers with important Baseline data on prevalence and exposure, which has not been evaluated thus far.
There are also limitations of this current monitoring effort. Because all samples are obtained from hunter-harvested birds, and none from other means such as birds captured and radio-monitored, it is difficult to discern population-level impacts on ruffed grouse by WNV at this time. This monitoring effort, however, will provide a better picture of overall prevalence and distribution of the virus and exposure to that virus.
There is some suspicion that juvenile birds, or those in poor condition, may be more susceptible to WNV. There is also evidence other factors such as habitat, nutrition, available cover and other things may also play a role in immune responses of ruffed grouse.
The report was careful to remind this is only year one of the study, with these results being from 2018. Sampling efforts continued through the 2019 season, with 500 kits allocated to hunters once again. That season, having recently concluded, samples are currently being tested. For the 2019 season, in order to obtain better age and sex data of the birds being tested, the DNR requested hunters also submit a rump and primary wing feather for identification.
For the 2020 season, another 500 kits are set to be distributed to hunters. This will mark the final year for the study.Beckie Gaskill may be reached via email at [email protected].