Why are Ohio’s grouse so hard to find?

Grouse need thick, young forest habitat

To understand why grouse declined, you first have to understand the kind of habitat they need. When talking about wildlife habitat, I like to separate two things:  Composition and structure.

Composition is what species of plants are present.

Structure is how that vegetation is arranged.

For ruffed grouse, structure is especially important. They do best in thick, early successional woodland with lots of stems close to the ground. That can include young trees, shrubs, blackberry, briars, and other dense vegetation.

The key is high stem density. A mature woods with large trees and an open understory may look beautiful to us, but it is not necessarily good grouse habitat.

What early successional habitat looks like

Good grouse habitat often looks messy.

There may be young trees growing close together. There may be fallen trees. There may be thick brush and low-growing vegetation. You may have plants reaching 10 or 15 feet high with a lot of dense cover underneath. That kind of habitat can develop after a timber harvest. It can also develop after trees die or fall naturally. Landowners can even create some of this structure intentionally by cutting selected trees and encouraging young woody growth. For grouse, this dense structure provides the kind of cover they need.

What succession means

Habitat does not stay the same forever. Vegetation changes through a process called succession.

Imagine an open field that is being mowed regularly. As long as you keep mowing it, grass and low vegetation dominate. Stop mowing it, and things begin to change. Weeds and shrubs move in. Blackberries and other woody plants begin appearing. Young trees such as ash and elm start growing. Over time, those trees get larger and thicker. Stem density increases. Eventually, after many decades, the area can develop into mature forest. That mature forest represents a later stage of succession.

For ruffed grouse, the middle stages, when the vegetation is thick and young, are often much more valuable.

Ohio’s forests have been getting older

One major problem for grouse in Ohio is that much of the state’s forestland has matured.

We have lost a lot of the dense, young woodland that grouse depend on. Instead of thick stands of saplings and shrubs, we increasingly have older forests with larger trees and more open understories. That habitat change certainly contributed to the decline in grouse numbers. But habitat loss by itself does not explain everything.

Predators are not the whole story

When a wildlife population declines, predators often get blamed immediately.  There are certainly predators capable of killing grouse.  But several species that have become more common in Ohio are not major grouse predators.

For example, the presence of birds associated with mature forests can actually tell us more about changing habitat than about direct predation. Likewise, other animals that have expanded their range into Ohio are not necessarily significant enough predators of grouse to explain the population collapse. The more important clue is much smaller.

The mosquito that changed the story

The most important factor in the decline of ruffed grouse is West Nile virus.

The virus is transmitted by mosquitoes. One of the mosquitoes capable of carrying it is the northern house mosquito. Ruffed grouse are highly susceptible to West Nile virus. Young grouse chicks are especially vulnerable. When chicks become infected, mortality can be very high. That means even if adult birds survive long enough to reproduce, losing large numbers of chicks can prevent the population from replacing itself. Over time, that becomes a serious problem.

Habitat decline made the population more vulnerable

West Nile virus did not arrive in a perfect grouse landscape. By the time it became an important mortality factor, Ohio had already lost a significant amount of young forest habitat. That matters.

A wildlife population living in abundant, high-quality habitat may be better able to recover from disease and other sources of mortality. A population already struggling because its preferred habitat is disappearing has much less room for additional losses. That is why the decline of Ohio’s ruffed grouse is best understood as a combination of factors. The habitat was becoming less favorable. Then West Nile virus added another serious source of mortality. For grouse chicks in particular, that additional pressure appears to have been devastating.

Why habitat management still matters

We cannot control every disease carried by mosquitoes. But landowners can influence habitat.

Creating or maintaining early successional woodland can provide better conditions for grouse and many other wildlife species that depend on dense young vegetation. That may involve timber harvesting. It may involve allowing old fields to begin growing into brush and young trees. It may involve creating openings or intentionally encouraging dense woody growth. The goal is not to turn every mature woods into young forest. It is to maintain a variety of habitat stages across the landscape.

What the loss of grouse tells us

Ruffed grouse are a good example of how wildlife populations can respond to long-term changes that are easy to overlook.

A forest can still look healthy to us while becoming less useful to certain wildlife species. As trees mature and the understory opens up, the habitat changes. Some species benefit. Others decline. Then disease, weather, predators, or other pressures can add another layer.

For Ohio’s ruffed grouse, the combination of disappearing early successional habitat and the arrival of West Nile virus appears to have been especially damaging. That is why many younger Ohioans may know what a ruffed grouse is but have never actually seen one. And that is a pretty dramatic change from the Ohio woods I remember.