Young ruffed grouse appear to be dying more over the summer; researchers want to know why

If ruffed grouse hunters enjoyed last year's season, they're in luck: The annual fall and early winter ritual that will begin in mid-September will be similar.

Or not.

Put another way: The Great Grouse Mystery continues.

Until recent years, spring drumming counts undertaken by Department of Natural Resources (DNR) staff and cooperators to estimate the size of the ruffed grouse breeding population correlated, approximately, to hunters' fall sightings and harvests.

Which, if still true, would mean the number of ruffed grouse that hunters see and harvest this fall will be approximately similar to the number they encountered and harvested last year — because the average statewide drumming count was the same both years: 1.5 drums per stop.

Yet whatever connected the spring drumming counts to fall sightings and harvests over a period of many decades seems to have disconnected, a phenomenon never more true than in 2017, when spring drumming counts showed an unprecedented 57% increase from 2016, yet many hunters that fall reported one of their worst seasons.

"Since the early 2000s the drumming counts have not been reliable forecasters of fall populations," said DNR grouse project leader Charlotte Roy, headquartered in Grand Rapids.

Integral to the conundrum is the belief that baby ruffed grouse are being hatched in spring but are disappearing as summer wears on. No one knows this for sure. But loggers and others in the woods during June and July have reported seeing "usual" or "average" numbers of grouse broods in recent years. But the young birds don't seem to survive until fall.

And while weather, which has been highly variable in recent years, with heavy periodic rainfalls across northern Minnesota, and aerial predators, which can be effective grouse killers, might be contributing factors, the leading suspect is mosquito-borne West Nile virus, which made its U.S. debut in New York in 1999.

The disease has been verified in multiple Pennsylvania ruffed grouse deaths and in three of 16 grouse found sick or dead in Wisconsin during the last three months of 2018.

For that reason, Minnesota last fall joined Wisconsin and Michigan in an attempt to gather enough samples from hunter-killed grouse to determine whether West Nile is at the root of the suspected spring-to-fall die-off and, if so, how widespread the problem is.

The issue is particularly important in Minnesota because the state is widely regarded as the nation's top ruffed grouse hunting destination. The number of birds living here is one measure, as are habitat quality and the vast acreages of northern Minnesota public lands open to hunting.

Populations of "Ol' Ruff" in more eastern states, meanwhile, which in the middle part of the last century nurtured much of the nation's storied upland hunting lore — including literate tales of double guns shouldered on autumn mornings and fine art paintings of setters on point — have declined as logging in the region has flagged and forests have aged.

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Wanting to collect samples last fall from 400 Minnesota ruffed grouse, the DNR instead gathered 273, an amount that far outpaced samples collected in Wisconsin and Michigan but was disappointing nonetheless, said Roy and Michelle Carstensen, DNR wildlife health group leader.

Disappointing as well was that many Minnesota samples came from birds killed later in the season.

"We wanted more birds that were killed earlier in the season because some grouse infected by West Nile might already be dead by the latter part of the season," Carstensen said. "We don't know yet how long after they're bitten [by an infected mosquito] they might die. The closer you get to the season where the virus is circulating, the more likely you'll detect the virus."

Results from a University of Georgia laboratory contracted to analyze Minnesota's grouse samples, as well as those from as many as 10 other states, were expected to be completed this spring. Now they might not be done until fall, and with another grouse season opening in just two months, the DNR has initiated an unprecedented ruffed grouse brood survey, in which foresters and others have been asked to record sightings of young grouse this summer.

The DNR is also gearing up to gather 400 more grouse samples for testing this fall, Roy said, adding that Minnesota members of the Ruffed Grouse Society (RGS), a Pennsylvania-based national conservation group, have assembled 600 testing kits for distribution in Minnesota.

"You have to have a lot of kits out there to get the number of samples back we're hoping to get," said Ben Jones, RGS president and chief executive officer. "It's a voluntary process, and it takes time for hunters to collect the samples. But it's important work, so we need to educate and motivate hunters to take sample kits with them into the field and complete them."

Hoping to incentivize hunters to sample downed birds, RGS will enter names of Minnesota hunter-cooperators into a drawing for a new shotgun and a hunting trip.

Additionally, wingshooters participating in the annual RGS National Hunt in Grand Rapids in October will be required to submit samples from birds killed during the two-day outing. Submissions last year were voluntary.

The annual Minnesota ruffed grouse harvest historically has ranged from about a half-million birds to more than double that number, the latter occurring during the peak of the grouse's 10-year population cycle.

Whatever the cause of The Great Grouse Mystery, continued hunting won't hurt the bird's breeding population, said Roy, the DNR grouse project leader.

"We are recruiting fewer ruffed grouse into the population," she said. "But the breeding population of these birds isn't in trouble."

danderson@startribune.com