WHILE the big summer die-off of adult ruffed grouse in 2017 remains a mystery, the state has released results from the first year of a three-year sampling program to test grouse for exposure to West Nile virus.

Out of 235 samples submitted by Wisconsin hunters in 2018, antibodies to the virus were confirmed in just 44 of the birds, or 19%, and they were listed as “likely” in another 24 birds. Together, that would total 68 birds or 29% of the samples.

Wisconsin’s totals were higher than Michigan and Minnesota, where a similar sampling effort showed virus exposure rates of 13% and 12%, respectively.

Few conclusions can be drawn from the one-year sampling according to Kent Van Horn, chief of the bird and habitat section in the Department Of Natural Resources (DNR) Bureau of Wildlife.

“The only thing we can say for certain is that there were grouse exposed to this virus that developed antibodies and survived,” said Van Horn. 

He said hunters have been wondering if the first-year results would answer the bottom-line question, which is whether a new disease caused a population-level impact on ruffed grouse in 2017.

“The results don’t answer that question,” he said.

Van Horn noted that bird exposure to West Nile could be different in every state for every year tested, because it all depends on the population of the infected mosquitos that carry the disease.

“That’s why we are doing a three-year sampling, because the results between the three states could be entirely different from year to year,” he said.

West Nile was first detected in Wisconsin in 2002 and it wasn’t detected in Wisconsin’s grouse populations until 2018, when three of 16 grouse that were found dead tested positive for the virus.

Last year’s sampling confirmed grouse exposure to West Nile but that doesn’t mean the birds were sick at the time of harvest. Even the only two birds found to have the virus present in their hearts had developed antibodies, which was determined by the accompanying blood test.

Hunters who submitted the 235 samples filled out forms that included questions about whether the bird was fat or thin, or whether it appeared weak or sick. But so far, the results of that information haven’t been shared by the department.

It appears there is good news in the fact that 71% of the grouse tested had not been exposed to West Nile virus. It’s also good news that so many birds that were exposed found a way to beat the virus on their own.

Van Horn said ruffed grouse are highly productive but short-lived birds. He said past research shows a 30% survival of adult grouse from year to year.

“Under normal conditions if you start with 100 adult birds in year one, there will be 30 alive in year two and just eight alive in year three,” he said. “They don’t live long but they do produce a bunch of young, with 13 eggs laid per nest.”

He said young-of-the-year birds make up the bulk of the annual hunting harvest, so the years with great recruitment are when hunters are most successful.

What the department knows for sure about the relationship between grouse and ailments such as West Nile is that the bigger and healthier the population, the more it can withstand such obstacles.

“What we are totally focused on is providing more of the young forest habitat that grouse and other species need to thrive,” said Van Horn. “Our best strategy is to maintain a healthy grouse population that can handle impacts from stressors such as disease and weather.”

That young forest habitat includes short-lived species such as aspen, birch, jack pine and tag alder, as opposed to longer-lived species such as maple, oak, white pine and old-growth forest types.

Van Horn said grouse also need a wide mix of uneven-aged aspen stands because new clear-cuts provide nesting protection while the mid-sized and older trees are needed for food, including leaves in fall and buds in winter.

The DNR is working hard on grouse research, habitat and management because it is one of the most popular upland game birds in the nation. They currently have a draft of the state’s first-ever ruffed grouse management plan.

“Wisconsin, Michigan and Minnesota harbor the best three-state population of ruffed grouse in the country, hands down,” said Van Horn. “People come to the northern forests from all over the country to pursue grouse.”

One example of that popularity was seen last month when the Ruffed Grouse Society staged its national Grouse Camp at Trees For Tomorrow in Eagle River, attracting 125 wannabe grouse hunters from 16 states.

Spring drumming in the North Woods, which is a strong indicator of population trends, hit a 13-year low in the spring of 2018.

That drop from what had been a steady rise toward the next population peak shocked wildlife managers because the decline occurred after they had documented a 30% increase in spring drumming in 2017.

The loss of thousands of adult birds during the summer of 2017 is still the big mystery, though it was one of the coldest, wettest summers in recent history.

Van Horn said cold, wet weather during May and June can devastate most of the brood-rearing success, as young birds without feathers are vulnerable to exposure during extended periods under those conditions.

The big surprise to hunters in the fall of 2017 is what happened to all the adults they left in their favorite spots the previous fall, because they disappeared.

There were widespread reports from hunters who had a hard time finding grouse that fall — enough for the DNR to convene special hearings and to propose an emergency rule to shorten the season.

Van Horn said the 48% increase in spring drumming this year has put the population back on track with the normal 10- to 12-year population cycle.