GROUSE drumming activity in the northern forest region dropped this spring to its lowest level since 2005, confirming last fall’s dismal hunting reports while puzzling wildlife biologists who had been tracking a population climb toward the next peak in the cycle.

Spring surveys on 43 established northern transects produced only 1.28 drums per stop, a 38% decline from last year and the lowest level recorded in the past 13 years.

The mysterious drop in adult ruffed grouse came after an encouraging spring of 2017, when drumming counts were up 30% over the previous year following a productive spring hatch and a population boost in 2016.

Because the last peak in the estimated 10-year population cycle was 2011, biologists fully expected the 2018 drumming counts would be similar to or higher than 2017 in line with historic trends in the cycle.

Mark Witecha, the DNR’s upland wildlife ecologist in Madison, said the decline is not consistent with typical grouse population cycles, which have been studied through roadside surveys since 1964.

Equally surprising to the DNR were the drumming counts in 2015, which were higher than expected for what would normally have been the low point in the cycle exactly four years after the 2011 peak.

“With this somewhat abbreviated low point in the population cycle in 2015, an increasing phase lasting several years is expected, so a decline in 2018 is not consistent with a typical population cycle,” he said. 

Witecha said it does however confirm the reports the department received from hunters last fall, that they were seeing far fewer birds than previous years.

So what happened? It’s anyone’s guess at this point, and the DNR’s report states that it might take some time to decipher if it was part of the grouse cycle or just an anomaly.

The only potential cause known today for this sudden drop in adult bird numbers is the cold and extremely wet conditions that prevailed from mid-May through July last year — which came after the 2017 drumming counts had clearly indicated that the adult population was on the rise.

Neither the DNR nor any other wildlife management organization has claimed there was anything else, such as an unexpected invasion of avian predators from the north or proof of some rare parasite or disease. And perhaps there’s another cause we haven’t yet identified. They are finding some grouse dead from the West Nile virus.

Knowing through this space that I’m a grouse-hunting addict, several readers who are avid hunters contacted me last fall to see if my observations matched theirs — all of which pointed to surprisingly dismal bird numbers overall.

As an example, one favorite covert where I had knowingly left at least 10 adult grouse the previous fall hardly had a bird in it when I arrived in the fall of 2017.

Usually it is cold, low-snow winters or an influx of predators during winter that lower adult bird numbers. And cold, wet springs can severely curtail brood production, but they don’t usually kill adult birds. But we really can’t say that any more, not after last year’s killer summer.

My hunch, which is just a wild theory, is that some adult birds died of exposure during those cold, rainy stretches and others became more susceptible to predation by owls and hawks.

I’ve witnessed broad-winged hawks hunting hard in the middle of the day in overcast, rainy weather. They seemed undaunted by the weather, as if they knew the odds of success were suddenly thrust in their favor.

According to the DNR’s report, the 2018 drumming results showed a 34% decrease statewide over 2017. That included a 38% drop in the northern forest region and a 29% decline in the central forest — the two areas of the state that comprise the primary grouse range in Wisconsin.

Roadside surveys to monitor the number of breeding grouse have been conducted by staff from the DNR, U.S. Forest Service, tribal employees and numerous grouse enthusiasts and volunteers since 1964.

Spring was late to arrive in Wisconsin this year, which forced the department to delay the drumming surveys in some parts of the state. Overall, survey conditions were “excellent” on 64% of the transects run, while 53% rated the conditions “excellent” in 2017. “Fair” conditions, the lowest rating, occurred on only 2% of the transects run this year, compared to 8% in 2017.

Ruffed grouse rely on dense, young forest cover that results from disturbances such as fire and logging. Beyond actively managing state-owned lands, the DNR is working to provided suitable grouse habitat through an extensive collaborative effort known as the Wisconsin Young Forest Partnership.

Witecha said the partnership provides technical and financial assistance for young forest management on private lands. It benefits grouse and many other species by helping maintain healthy and diverse forest communities.

On federal lands, the DNR is also helping improve grouse habitat through a Partnership Authority that allows the state to plan and conduct a certain number of timber sales, which has boosted logging and habitat development in recent years.

Whether this is an anomaly or part of the cycle, the fact of the matter is that drumming surveys show grouse numbers are currently at 13-year lows — even lower than the 2015 low that biologists believed to be the bottom of the cycle.

It’s quite the mystery on what exactly happened to our adult grouse during last spring and summer. They took an unprecedented hit.

We went from the high hopes of a 30% increase in spring drumming, looking like another population peak was near, and plummeted to the worst numbers in more than a decade.

We may never know why. All we can hope for is that we begin to climb, once again, toward another peak in grouse numbers.