Biologists in Pennsylvania and neighboring states agree that ruffed grouse have been generally declining for the past several decades. Grouse hunter numbers have dropped as well. The ranks of Pennsylvania ruff chasers dwindled from around 200,000 in the mid 1990s to 134,000 in 2003, the last year the Game Commission conducted its game take survey.
The conventionally accepted prescription to reverse those trends is to cut more forest, encouraging the regeneration of the thick cover grouse need. Wisely planned cutting can improve conditions for grouse, but recently reported research identifies another critical need of the species that is seldom acknowledged by grouse hunters or grouse managers -- acorns, the fruit of mature oaks.
Researchers in 12 study sites examined grouse habitat selection, diet, reproductive success and mortality from 1996 to 2002 in the Appalachian Cooperative Grouse Research Project (ACGRP). Study sites were chosen in forested, mountainous regions of Kentucky, Maryland, North Carolina, Ohio, Pennsylvania, Virginia and West Virginia. To better understand the ecology of this popular bird, scientists placed transmitters on hundreds of grouse, including tiny devices on grouse chicks, monitored video cameras concealed at nests and analyzed the crop contents of hundreds of grouse killed by hunters.
Ruffed grouse range from Alaska, south and east across forested reaches of Canada, into New England. The core of ruffed grouse range is the forested basin surrounding the Great Lakes. Southward from that core arcs a prong of isolated range along the Appalachian Mountains, as far south as northern Georgia.
Pennsylvania is considered part of the Appalachian grouse range. ACGRP researchers compared their findings to data from grouse populations in Minnesota, Michigan, Wisconsin and neighboring Canadian provinces. They concluded that mountain grouse must forage longer and farther to find quality food, have lower reproductive success, and are more exposed to predation, especially from hawks, owls and nest-raiding mammals, than their northern relatives. The study suggests that in a challenging environment, well outside the bird's central range, the periodic production of acorns in Appalachian forests is what sustains the species.
Consider these key findings of the ACGRP research:
Grouse populations in Appalachian forests are nutritionally constrained, particularly in late winter and early spring before breeding. While northern grouse subsist on the more dependable flower buds of aspen, Appalachian grouse forage far and wide for a more diverse, lower quality, diet unless oak mast is present. Where and when oak mast is available, Appalachian grouse utilize it heavily to build fat reserves that enable successful breeding, nesting and brood rearing.
Chick survival was greater in years following heavy oak mast production the previous fall, indicating that reproductive success in the region is strongly influenced by the availability of acorns.
Grouse home range size increased in years following acorn failure, exposing the birds to greater risk of predation.
While traditional grouse management recommendations stress the importance of cutting to encourage early successional cover, the ACGRP work demonstrates that mature oak stands are essential elements of grouse habitat in Pennsylvania.
For concerned grouse hunters, it is difficult to escape the suspicion that over-abundant white-tailed deer may be placing additional stresses on grouse in a region where survival has always been a challenge.
The 61-page AGCRP final report never mentions deer, but a comparison to other scientific work strongly suggests that browsing of oak seedlings and direct competition for acorns by deer over recent decades has made the already tough existence of mountain grouse even tougher.
Current research at Penn State University found that 50 percent of oak stands studied do not regenerate after timber harvest, and that fencing oak stands to exclude deer before harvest can encourage oak regeneration.
"The most important thing is that we are beginning to understand the critical importance of keeping deer pressure low for several years in advance of harvest," said Jim Finley, Penn State professor of forest resources.
Abundant deer not only prevent new oak forests from developing, they compete directly with grouse for acorns available on the ground. In one study, deer consumed nearly three- quarters of all the fallen acorns in Pennsylvania red oak stands, largely monopolizing the mast crop.
Another recent study by the University of Pittsburgh found that acorns are more intensely and selectively foraged by mice, chipmunks and other small mammals in habitats where the understory has been over-browsed by deer.
Newly acquired knowledge about the importance of mature oaks, and the apparent impacts of over-abundant deer on grouse should enable land and wildlife managers to better accommodate this game bird in Appalachian forests in the future.