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Making Sense of the Cycle

A young hunter moves in on the seasoned setter’s point. He’s already missed three grouse the dog has nailed this morning, plus five wild flushes. He is in his first season, naive, and still searching for that first grouse. His father watches, with gun broken over his arm, anxious, growing more desperate for his son to hit a bird. The grouse streaks out low and straight, the son’s 20 cracks, and a puff of feathers wafts in the breeze as the bird tumbles to the earth.

Throughout his teenage years, those short walks through the woods with the setter turn up fewer and fewer grouse, so his attention switches to ducks and geese and Labrador retrievers. Instead of starting out the morning getting soaked in the dew-covered ferns and aspen cuts, he hunkers down along a marsh and waits for whistling wings.

Now, in his early 20’s, the young man moves in on his setter pup’s nervous point. She has already bumped a half-dozen grouse this morning, but she has begun to figure it out.

Her flanks are quivering as she stares at the base of a clump of witch hazel, and now she rolls her eyes slowly to see if he is coming. He moves in, his hands clenching the old 16-gauge, the one his father gave him, and the dog holds as the grouse thunders skyward.

The boom echoes through the woods as the bird falls through yellow aspen leaves. The young man stuffs the empty shell into his pocket as a memento of his puppy’s first, staunch ruffed grouse point.

Somewhere, far away and earlier in the year, a wildlife biologist makes the final mark on his data sheet and pulls out two other, yellowed data forms. He holds them together — the numbers from the drumming count he just completed are almost equal to those he did 10 years prior on the same route. Comparing those two counts to the one of five years ago, he sees the telltale signs- a dramatic dip in the number of drummers. High to low to high: The cycle is back on the upswing.

Ruffed grouse undergo regular shifts in their population density, from years of almost record highs in a small covert, to scarcely any birds in the same area. Many other wildlife species experience the same thing, and these fluctuations have been generally called cycles. For ruffed grouse, the cycle goes through one complete high-low-high revolution in about 10 years. Anyone who regularly busts through the cover for grouse knows full well before the season begins whether that year will be in the “top of the cycle” or if it would be better to chase those mallards seen circling the lake. Experienced hunters can trace the cycle through their hunting journals, seeing from one year to the next, in the same covert, that the number of flushes went from a bird every few minutes to barely finding one the entire day. In a number of states, wildlife biologists conduct regular surveys throughout the year to get an idea of the size of the grouse population. These can include drumming counts in the late winter, early spring, and even fall; brood counts in the summer; and hunter harvest surveys after the shooting season. More in-depth studies have begun to include radio-telemetry to track birds throughout the year, providing valuable data on mortality, habitat usage, food habits, breeding and nesting characteristics and home range. All of these factors can be valuable pieces of the grouse cycle puzzle.

For many years, the cycle was a mystery, and there are some today who claim it is still so. There are, however, credible theories that have been put forth to explain the 10-year grouse cycle, and though none of them has been proven conclusively—and it’s doubtful they ever will—they lend insight into the factors that play on a grouse population.

THE PREDATOR/PREY RELATIONSHIP

Back in the 1960s, Lloyd Keith proposed the predator/prey relationship as a means of explaining the grouse cycle. Since then, other studies have supported his, which probably explains better than any other theory why one year your dog points every hundred yards, and another year she doesn’t stop all day.

The ruffed grouse, being a bird of slightly more northern climes, is tied inex-tricably, it seems, to the snowshoe hare, whose southern distribution overlaps the grouse’s northern range. We have all heard of the notorious goshawk and greathorned owl as the grouse’s archenemies. This, then, is our cast of characters.

The snowshoe is the main staple for many predators in the far north, in particular the goshawk and great-horned owl. Hares reproduce, well, like rabbits, and quickly, an area can be flooded with hares. The predators rub their wings together at this fish-in-a-barrel opportunity. However, because there are so many hares, the snowshoes begin to eat themselves into trouble: Vegetation disappears from the onslaught of the burgeoning population. Soon, due to the lack of food and adequate habitat, which in turn leads to poorer reproduc-tion, a population decline begins. The predators, feasting on the abundant population, accelerate this decline as they pick off hares that wander out into unlikely places in search of scarce food. Eventually, the predators begin to turn up fewer and fewer of their white dinners.

Meanwhile, sitting comfortably on an aspen branch somewhere hundreds of miles south of this hare-predator soap opera, a ruffed grouse nibbles at an aspen bud. Like a lightning strike, a hungry goshawk from the north slams into the grouse leaving behind a few wispy feathers. The hare decline in the north has forced the predators to search out other foods. Sometimes, this means traveling farther south to find adequate food supplies. The first on the list? Often it is Mr. Grouse.

The grouse had also been enjoying high numbers − a peak in the cycle − while the hares were abundant because the predators had other meal tickets. But now, with the drastic decline in the snowshoe population and the predators desperate for food, the goshawk and great-horned owl begin to pick off grouse while the hares get a break. This creates a low in the grouse cycle. Because the grouse could never compare to hares in terms of providing a stable food supply, the predators find themselves in dire straits. Their populations begin to decline as both the hare and grouse become harder to find.

While on their respite from predator ambush, the hares begin to repopulate in the regenerating vegetation. The small predator population starts to find more hares, shifting back to their preferred prey choice. The hares reproduce much more prolifically than do the raptors, so the hare population is not hindered by this new predator assault. With a breather from the aerial attack, the remaining grouse form a basis for the population to get back on its feet. Now, all three populations are increasing again.

FOOD POISONING

Food poisoning received some measure of support from a noted ruffed grouse researcher, the late Gordon Gullion. One of the main foods of ruffed grouse during the winter are aspen buds. These big, nutritious buds can quickly fill up a grouse’s crop, allowing the bird to get back into cover and digest the food. This doesn’t leave much of an opportunity for a cruising goshawk to come across a feeding grouse.

Just as some other plants can produce toxins to protect themselves, aspen can periodically produce chemicals that make their buds less palatable to grouse. This forces the bird to search out new food or travel farther in cold weather to find food. Perhaps a food item of less quality is discovered and the grouse now must take twice as long to fill its crop and then fly or walk farther to its roost or cover. Because of the greater travel and feeding time, it must feed more often to replace the calories burned in searching and consuming the food. Now how long does that goshawk have to find a meal?

So, unpalatable aspen buds lead to the grouse’s spending more time in search of food, which means more exposure to predators. Since this is happening in the winter, more grouse taken by predators means fewer grouse come breeding season, which means fewer broods, leading to a small population come autumn.

More research is needed in this area, but it has been noted that in parts of the South, where aspen does not play a big role in the diet of grouse (or, incidentally, where the snowshoe hare-predator relationship is nonexistent), grouse cycles have not, or have rarely, been observed.

DISEASES

Some researchers have put forth the idea that diseases might cause or contribute to the grouse cycle. One disease in particu-lar, tularemia (rabbit fever), has been known to undergo fluctuations in its virulence, and that, coupled with fluctuations in the population of its carrier, the rabbit tick, could cause periodic die-offs of grouse. Even if the disease doesn’t kill the bird outright, it could weaken the grouse, resulting in a bird that can’t escape a predator, is more easily killed by harsh weather, or is too weak to successfully breed or nest.

However, it is believed that diseases do not have as great an impact on grouse populations as once thought. Examinations of grouse populations throughout the cycle have revealed that diseases are always present, but none are capable of causing the dramatic population shift characteristic of the cycle. Disease could be a factor, but it is probably not the sole cause.

A COMBINATION OF FACTORS

Though some would argue that hunters are the ultimate cause of population declines, the great hunting debate has spanned generations, and legal, lawful hunting has been put to rest as a cause. Habitat plays a key role in every facet of a grouse population, or any wildlife population, but habitat is not a cyclical entity. Periodic habitat management techniques or habitat destruction outbreaks can cause extreme benefit or sometimes severe damage to a local grouse population, but the cycle is too regular, and is present even in areas with no great habitat modifications. However, it is important to note that adequate habitat can only help grouse, and in that regard, we should all strive to see that good grouse habitat is maintained, created, or restored.

The ultimate cause of the grouse cycle is likely due to a number of factors woven together. Take, for example, the three theories proposed here. A large hare population means that predators are not eating grouse. If this coincides with a time when aspen buds are tasty and a grouse disease is held in check, a grouse population could flourish. Now, let’s say the hares are down, which means the predators are focusing their efforts on grouse that just happen to be a little bit easier to find and catch because they’re in the open while searching for less nutritious food or are weakened by disease. A low point in the cycle ensues. We can go back and forth, putting in a number of factors at various levels and intensities and still, we would get a time of high grouse numbers, followed by a low about five years later, and then back up again in five more years. It is just the way of grouse, the way of a number of other wildlife species.

Just be sure to enjoy those seasons when the birds are flushing from every clump of cover. You know which one it will be—just check your hunting journal.

*Republished with permission from “Making Sense of the Cycle”
by Jason A. Smith, 1998. The Upland Almanac, Autumn 1998.
1998 by Jason A. Smith. Artwork by C. Smith

Jason A. Smith