Tovar Cerulli

“Good Year, Bad Year:
Ruffed Grouse Populations Ride a Roller Coaster”

Northern Woodlands, Winter 2006

“Everyone knows . . . that the autumn landscape in the north woods
is the land, plus a red maple, plus a Ruffed Grouse.
In terms of conventional physics, the grouse represents only a millionth
of either the mass or the energy of an acre.
Yet subtract the grouse and the whole thing is dead.”
—Aldo Leopold

No autumn sound makes my heart jump like the explosive rush of a grouse bursting from cover a few yards away. Last fall, however, that was a rare occurrence. Across northern New England, the word from the woods in 2005 was that grouse numbers were down, way down. In past years, an October stroll along the old railbed near our house in northern Vermont would usually send a few feathered rockets hurtling skyward. And from winter-frosted windows, I’d see plump birds testing their balance as they leaned out, plucking buds from apple branches in the front yard or from the upper reaches of nearby aspens. Last year, I encountered few in the woods and none by the house.

Noticeable population changes in ruffed grouse are bound to spark discussion of the “10-year cycle,” a boom-to-bust phenomenon that has attracted decades of research. Grouse numbers in a given area can drop by a factor of 10 or more, and they can drop precipitously, sometimes in a single year. The puzzle is complicated, for grouse populations fluctuate for different reasons across their impressive geographic range, which stretches from the southern Appalachians north to Labrador and west across the Great Lakes and central Canada to parts of Alaska.

Studies have frequently focused on their prime range in Canada, where many biologists contend there is a clear cycle that moves in waves across the continent. This pattern is poorly understood and subject to various conflicting theories. Still, it is generally agreed that grouse cycles north of the border result from predator-prey relationships that include another key prey species, the snowshoe hare, whose populations exhibit an 8- to 11-year cyclical pattern. The hare cycle, in turn, is based on their relationship to food sources and local predators, especially northern goshawks, great horned owls, and Canada lynx.

As hares increase, so do predators. When growing predation and diminishing food sources lead to a crash in hare numbers, predators necessarily shift more of their attention to ruffed grouse, triggering a rapid decline in that population as well. With hare and grouse on the wane, predators are forced to look farther afield; large numbers of goshawks and great horned owls fly south into northern parts of the Great Lakes region, where both prey species are again hit hard. With less food available, predator numbers decline, setting the stage for a comeback of their favorite dinner, hare, and their backup meal, grouse. Though avian predation accounts for most of its adult mortality, the grouse has the good fortune of not being a staple food for any one predator.

Here in the northeastern U.S., the existence of a predictable 10-year cycle is much more doubtful. To begin, we must turn to Gardiner Bump, Robert Darrow, and their colleagues, whose long-term studies in New York state culminated in the 1947 publication of The Ruffed Grouse: Life History, Propagation, Management. The book was a landmark achievement in the study of wildlife and remains one of the most widely referenced sources on grouse. Darrow’s chapter on fluctuations in grouse numbers suggested “a tendency for major declines in abundance to recur at intervals of eight to ten years” yet noted that the trends were somewhat unpredictable. Considering these ups and downs, Darrow conjectured that weather was the most significant factor. Specifically, it appeared that cold, wet conditions in the weeks immediately after hatching might set the stage for high chick mortality.

Six decades later, the causes of population patterns remain uncertain, and biologists in the Northeast still cite spring weather as the most likely factor. Here, grouse nest in May and hatch by early to mid-June. Michael Schummer, a wildlife biologist with the Maine Department of Inland Fisheries and Wildlife, notes that even before nesting, difficult weather can affect a hen’s condition and her ability to produce a full-size clutch of healthy eggs. When first hatched, grouse chicks have no feathers, only down. The hen broods them at night and during cold weather but can’t do so constantly. So, with little other protection from the elements, the chicks may fall prey to pneumonia-like conditions or may simply be weakened and less able to survive the months ahead. It has also been suggested that wet weather reduces the opportunities for grouse chicks to feed on insects, and that a hen’s wet feathers may give off a stronger odor, increasing the odds for mammalian predators such as foxes.

Maine’s grouse population is robust in comparison to the rest of New England’s, yet even there it was at low ebb last fall. The preceding spring was the first in over two decades to have both below-average temperatures and significantly above-average precipitation. Looking back to May 2005, Schummer recounts that in some parts of the state, it rained 25 of 31 days. The National Weather Service reports that over 17 inches of rain fell from March to May, making it one of the state’s wettest springs in over a century. Maine, like the rest of New England, averages less than 11 inches for those three months.

Unlike their chicks, adult grouse are amazingly hardy. Though often affected by nutritional deficiencies and a variety of parasites, bacteria, and viruses, they are rarely killed outright by such factors. Rather, these may contribute to population changes indirectly, by making the birds more vulnerable to predation. Weather plays a similar role. In winter, for example, grouse burrow into snow for warmth and protection; shallow snow or an icy crust can prevent snow-roosting, robbing the birds of energy and exposing them both to bitter cold temperatures and to predators. Food can be a challenge, too, and not just in its scarcity: plants sometimes produce defensive chemical compounds that make them less palatable and nutritious. Research by experts including the renowned Gordon Gullion suggests that if this occurs in a stand of aspen, the grouse’s staple winter food source, the birds are forced to take the risk of foraging more widely.

From central New England southward, grouse populations are generally lower and more stable, hinting at the absence of factors that cause extreme fluctuations and cycles in northern areas.

Though ruffed grouse is the most widely hunted game bird in North America, biologists generally agree that today’s hunting has virtually no effect on overall population. Like many species, grouse were heavily exploited by market hunters until the early 1900s. According to Gardiner Bump, “grouse bounties” were even offered to counter their winter decimation of apple orchard buds in Massachusetts. Diminishing numbers eventually led to the banning of market hunting and the establishment of seasons and bag limits. But even with hunting closely regulated, conservation officials believed through the 1930s that the shotgun was having a significant impact.

Opinions began to shift in the following two decades as hunting seasons were opened and closed with no apparent effect on the rise and fall of grouse numbers. Whether hunted or not, about the same number of birds survived. Biologists came to the conclusion that grouse taken by hunters would, if not taken, die in similar numbers of other causes during the winter. In Maine, Schummer notes that hunting accounts for only about 15 percent of grouse mortality, whereas avian and mammalian predation accounts for about 80 percent. Exceptionally high hunting pressure can be detrimental. Research on public land in the Midwest has shown harvest rates as high as 60 percent and has concluded that such levels likely have a significant impact, especially where fragmented habitat reduces the opportunity for other grouse to repopulate the area.

Whatever factors explain quick downturns in population, how do we account for the flip side of the coin, the often dramatic resurgences? It is a matter of reproductive potential. Grouse, like rabbits and hares, are prolific breeders. Hens reach sexual maturity in their first year, and research indicates that almost all hens nest each spring, laying an average of 12 eggs. As Bump and his colleagues pointed out, a single pair could multiply to over 33,000 birds in just five years, assuming a 100 percent survival rate. Thus, under favorable conditions, grouse populations can rebound with astounding speed, despite the inevitable plundering of nests and losses to predators. In the autumn of 1995, the Maine woods were thick with birds; Schummer recalls that “the grouse were like a black fly incident.”

Tracking these fluctuations is difficult because grouse are hard to count. Population estimates are based on several measures, all of them imprecise and affected by uncontrollable variables. The most common method is the roadside drumming count: in April or May, a researcher drives along a predetermined route, stopping at designated points and counting the drumming males heard in a certain time period. Other counts include birds taken by hunters, or sightings reported by those hunting other game.

This unsolved mystery of ebb and flow leaves ample room for speculation. But the dramatic short-term dynamics don’t appear to affect populations in the long run. Long-term trends revolve around a single factor: habitat. Grouse depend on early successional forest growth, because closely spaced, small-diameter trees offer them crucial cover from predators. And aspen, a pioneer species, is their preferred winter food source. Whatever else biologists may disagree on concerning grouse, they are unanimous on this: where young forest growth is absent, grouse are in trouble.

Photographs from early twentieth-century New England provide windows onto grouse history. Vermont wildlife biologist Cedric Alexander notes that the widespread clearing of land for agricultural use eliminated much of the birds’ habitat. Subsequent re-growth, in contrast, provided a period of excellent early successional woodland and prime grouse habitat. Gary Goff, Cornell Cooperative Extension specialist and director of New York’s Coverts Program, points out that similar habitat follows in the wake of natural events such as fires, hurricanes, ice storms, and defoliating insect outbreaks. Today, with smaller land parcels, strong wildfire control, and changing forestry practices that limit clearcuts, the forests of New York and New England are maturing. Maine is the exception. There, large areas of contiguous forest are intensively managed by commercial timber operations, and, while clearcutting has been reduced, the level of even-age cutting continues to be heavier than elsewhere, resulting in continuous production of sapling habitat and a generally strong grouse population.

U.S. Forest Service surveys show that in 1968 more than half of New York’s forests were in the sapling and seedling stage; by 1993, that type of forest was down to less than 20 percent, while larger sawtimber had climbed from 30 percent to over 50 percent. Not surprisingly, the state’s grouse populations have been declining since the 1960s, says New York Department of Environmental Conservation biologist Mike Murphy. As Goff puts it, “Habitat in the Northeast is shifting from ideal grouse habitat to ideal turkey habitat.” A longer-term look at the forests of Massachusetts is even more dramatic: in 1920, they consisted of about 80 percent saplings, but by 1998 were 80 percent sawtimber. Likewise, Michael Gregonis, a biologist with the Connecticut Department of Environmental Protection, points out that although his state is 60 percent forested, only a very small portion is in the early successional stage, resulting in few grouse.

State wildlife agencies across the Northeast are working hard to improve the long-term prospects for the ruffed grouse. In the past year, Wildlife Action Plans were issued by New York and each New England state; every state except Maine listed ruffed grouse as a “Species of Greatest Conservation Need.”

Good grouse habitat is being lost both to maturing forests and to sprawl. Officials estimate that more than 30 acres of Massachusetts forest are leveled for construction every day, and the effect is spreading. Julie Robinson of New Hampshire Fish and Game observes: “In the southern part of New Hampshire, the habitat that used to support grouse is now a housing development.” The state has lost 17,000 acres of open space annually for the past 5 years; in its southeast region, no drummers were heard in the 2005 count.

Ruffed grouse have been on the continent for well over 20,000 years, surviving changes that pushed many other species over the brink of extinction. Grouse will undoubtedly survive much longer. Here in the Northeast, though, the brightness of their future depends on us and the influence we have on their habitat.

© 2006 Tovar Cerulli