Is forest management harming songbirds?

It has been several years since Richard DeGraaf has heard a whip-poor-will sing in the big woods of New England. As chief research wildlife biologist for the USDA Forest Service's Northeast Forest Experiment Station, DeGraaf recalls when the countryside of northern Massachusetts, Vermont, New Hampshire, and southern Maine rang with the bobolink's bubbling refrain, the meadowlark's musical whistles, and the brown thrasher's repititious trills. No more. These days, he says, it's a treat to even hear the boisterous "drink-your-TEEEEE!" of the rufous-sided towhee.

To the untrained ear the loss of those calls might go unnoticed, but DeGraaf and other scientists know that the dwindling of this avian chorus is symptomatic of an alarming verity in the forests of America: Many of our most beloved songbird species are in a population tailspin. According to the U.S. Fish and Wildlife Service's Breeding Bird Survey, dozens of the nation's songbird species have experienced significant population decline since the survey began in 1966.

Not since the DDT scare, which Rachel Carson described in her 1962 Silent Spring, has the nation's love affair with wild birds been so imperiled, and this at a time when bird-watching and feeding has swept new millions of Americans into a closer relationship with waterfowl, shorebirds, and the warblers that bejewel our springtime forests. As researchers from coast to coast scramble to find answers, ornithologists and forest managers are asking a crucial question: How does timber harvest affect songbirds, particularly those long-distance migrants that are experiencing steep population declines?

For a number of reasons - the public's distaste for clearcutting, the abandonment of farmland in certain regions, increasing suburbanization in others - the nation's forests are changing (see The Great Green East: Lands Everyone Wants, on page 13). In New England, the mosaic of small farms and forestland is disappearing as farms are abandoned. Through much of the mid-Atlantic, shopping centers and housing developments are nibbling at forest fringes. Across the East forests are aging, while in the Rocky Mountains fire suppression is changing the biological character of entire ecosystems. Such changes have led to a host of questions about avian biodiversity and our remaining forests:

* How do birds fare in smaller woodlands?

* How do bird communities differ in young woods vs. mature forests?

* And how can timber harvest be made most compatible with a healthy, diverse avifauna?

It is, says Richard Yahner, professor of wildlife conservation at Pennsylvania State University, "an exciting time. We are rethinking our means of managing a forest for biodiversity." And in that there is both opportunity and dilemma.

Early Warnings

Among the birds posting significant population declines are many species in the group known as neotropical migrants. These long-distance fliers breed in North America and fly south to Mexico, Latin America, and South America for the winter. About half of the some 650 birds species found in the U.S are in this category; about 30 of those face precipitous declines nationwide or in significant portions of their ranges. Many of those birds are forest-interior species, creatures that prefer to nest in large, heavily wooded sites. Among them are the wood thrush (down an average of 1.9 percent per year from 1966 to 1993, according to the Breeding Bird Survey), cerulean warbler (down 2.6 percent per year), and eastern wood-pewee (down 1.6 percent per year).

Others are early successional migrants, birds that prefer nest sites in younger vegetation, such as overgrown fields, patches of clearcut forests, and places where natural disturbances have cleared the woods of its forested canopy. Among these species are the painted bunting (down 3.3 percent per year), field sparrow (down 3.3 percent), and golden-winged warbler (down 2.3 percent).

To the layperson these declines may seem rather small, but like compounded interest, their effects over time are startling. "At some of these rates," warns Robert Askins, a Connecticut College professor of zoology and a leader in studies of bird population trends, "it wouldn't take long for a population to be cut in half, then a quarter, then an eighth."

When the alarm bells first began ringing over songbird declines in the late 1970s, two early suspects were identified. Deforestation in the neotropical wintering grounds seemed an obvious culprit, but that wasn't enough to explain the downward spiral in some species whose wintering grounds are largely undisturbed. In the early 1980s, researcher David Wilcove of Princeton University ran a nest-predation experiment in which artificial nests were stocked with quail eggs and placed in small, medium, and large forests in both rural and suburban settings, and in a control site in the large, unfragmented Great Smoky Mountains National Park. His findings threw open a window of possibility: Rates of predation by raccoons, opossums, skunks, house cats, and blue jays were astounding. In some smaller fragments nearly 100 percent of the quail eggs placed in the artificial nests were destroyed, while only one of 50 Great Smokies nests was raided. Clearly, nest predation in fragmented forests is one factor in the decline of songbirds.

A few years later, in the late 1980s, another piece of the puzzle emerged. Studies by Scott Robinson in central Illinois uncovered astonishingly high levels of cowbird parasitism of songbird nests in the fragmented forests of the Midwest. Brown-headed cowbirds, a grassland species that once followed the great herds of buffalo to feed in the grazed and trampled grasses, are brood parasites. Instead of building their own nests, cowbirds lay an egg or two in the nests of"host" species - a single female may lay as many as 40 eggs in other nests - often tossing out the resident eggs in the process. After hatching, the larger and fast-growing cowbird nestlings outcompete their "siblings" for food, with disastrous results. In some of Robinson's sites nearly 80 percent of wood thrush nests - his target species - were parasitized by cowbirds.

The observation that parasitism and predation are often higher near forest edges have led scientists to term these "edge effects," and they pose a specific question for forest researchers: If forest edges in suburban and agricultural areas are the site of intense parasitism and predation, how does timber harvest, which creates edges similar to other modes of fragmentation, affect nesting and reproductive success? Insight into the answers is only now becoming clear.

Broadly speaking, timber harvest changes the forest landscape in two primary ways, says Frank Thompson, project leader and a research wildlife biologist at the USDA Forest Service's North Central Forest Experiment Station in Missouri. Harvest by clearcutting removes mature stands and replaces them with a mixture of early-, mid- and late-successional habitats. But those alterations occur over time. What changes immediately is the distribution of habitat types in the forested landscape.

"We know [timber harvest] creates habitat for some species and removes habitat from others," Thompson says. "What we know less about is the implications of spatial distribution." Harvest patches can be small or large, clustered together, or spread through the landscape. "We know edge effects occur in some landscapes and not in others, but the question we don't have nailed down," Thompson explains, "is how edges created by timber harvest affect bird populations. Are there similar kinds of forest fragmentation mechanisms, such as predation and parasitism, at work relative to timber harvests?"

To investigate potential population level impacts, Thompson used a computer to develop a 1,000-hectare (about 2,500-acre) simulated forest, punched in a range of moderate clearcut and group-selection harvest sites of 10 to 40 hectares (about 25 to 100 acres), populated the landscapes with birds, and ran population models over a 150-year period. That model suggests that changes in the age of forest patches affect populations more than edge effects that result from clearcutting. Longer and shorter rotation times were paralleled by higher and lower population levels.

"The model suggests that selection cutting could have a much greater edge effect because it creates numerous smaller openings. But the benefit to birds could be that it maintains mature trees across the landscape." Thompson points out that the model simply assumed that in one scenario edge effects occurred and in the other they did not. "We don't know how that will translate in the field," he says. But if there are edge effects with selection cutting, they could be worse than those associated with clearcutting.

Thompson's hypothesis is that nonforest uses in a landscape - agricultural fields or suburbanization, for instance - do more to regulate the number of nest predators and cowbirds than does regulated harvest within the forest. Cowbirds specifically require short grass or some other agricultural habitat in which to feed; predators such as raccoons, house cats, and opossums are fairly dependent on these same suburban or agricultural areas. In heavily forested landscapes, Thompson surmises, "whether you do clearcutting or selection cutting or no cutting at all, we may still see similar levels of nest predation, because there are so few cowbirds and so few predators."

Bird density and reproductive success, however, are two different elements. Thompson, Robinson, and other colleagues are now studying how forestry management practices affect avian reproduction in Missouri, Illinois, and Indiana.

That, says Askins, is the missing piece of information. "Bird densities can give you a distorted view," he says, in that immigration of birds into a landscape can keep bird numbers relatively high while their reproduction rates plummet. The Connecticut professor is particularly concerned about the ancillary effects of timber harvest. Forest management practices require an infrastructure of logging roads that lead into the forested landscape.

Such an infrastructure, says Askins, worries him more than the clearcut patches themselves. Logging roads often turn out to be permanent roads, he says, and there is good evidence that they can bring predators and cowbirds deep into a forest landscape. As clearcutting practices give way to selection cutting, in which single trees or small groups of trees are cut in a harvest site, Askins is concerned that an ever-growing logging-road system will in effect fragment forests to an even greater degree. For the foreseeable future, he says, large continuous forests such as national and some state forests "may become increasingly important because they probably produce a surplus of forest birds for other areas."

But whether they prefer large forest or woodlot, mature oak hickory woods or shrubland habitat, birds are changing the ways they use the nation's forests. In that they have no choice, because the nation's forests are themselves in flux.

The Evolving Forest

North American forests have changed dramatically over the last half-century. While the role of fire in forest maintenance has been reexamined since the Yellowstone blazes, fire was by no means the only mechanism of forest disturbance in pre-settlement times. Massive windfalls of up to 9,000 acres were recorded in 19th-century Wisconsin, according to Craig Lorimer, a professor of silviculture and forest ecology at University of Wisconsin-Madison, and Native Americans, along with hurricanes, insects, and drought, created other large openings in the pre-settlement forest canopy.

Over the past half-century, timber harvest and agricultural abandonment have been primary means of maintaining early successional growth, but many former farm fields are now maturing into timber, and large openings created by clearcuts are a thing of the past in many regions. In many areas the nation's forests are growing older. In others they are simply growing smaller and more disjunct.

In the mid-Atlantic, suburbanization is a primary culprit. In much of the region, says Yahner, forest fragmentation "is virtually permanent. Once you build a shopping center, the forest is gone. That differs from fragmentation created by timber harvest that will revert back to forest. There are very different effects on the landscape."

In the Midwest, forested landscapes have been altered through agriculture, development, and timber harvest. Thompson reports that many parts of the Midwest have posted small increases in forest cover over the last decade, but much of the forest remains highly fragmented and disjunct. With four other collaborators he recently published a study in which data was pulled from Missouri, Indiana, Illinois, Wisconsin, and Minnesota to observe avian reproductive success patterns in various fragmented landscapes. In the most fragmented landscapes, Thompson says, reproductive rates were so low for some species that the birds would not have been able to replace their natural mortality.

In the West, Deborah Finch of the Rocky Mountain Forest and Range Experiment Station reports that "harvesting in the Rockies hasn't had the impact it has elsewhere." Instead, she points to the impacts of fire suppression. "There is a lot of discussion among my colleagues that a clearcut does not replicate a burn site" as regards bird use, Finch says. After a burn many insects appear that serve as a prey base for birds, and some western bird species have evolved to take advantage of habitats created by large fires. The black-backed woodpecker, for example, has evolved protective coloration that mimics the trunks of charred trees, and species such as olive-sided flycatchers use snags left by wildfires as perch sites. Elsewhere in the Rockies the growing demand for aspen might be affecting a number of neotropical migrants that favor aspen groves - the warbling vireo, orange-crowned warbler, western wood pewee, and dusky flycatcher among them.

In few places, however, have a region's forests changed on the level exhibited by the forests of the Northeast. In 1850, says DeGraaf, about 90 percent of the arable land in central and southern New England had been cleared. By 1960, those figures were reversed: Some 90 percent of the arable land was forested. With the abandonment of New England's small farms during decades of economic depression, the character of the big woods changed dramatically. "Except for the industrial timberlands in Maine, there is probably more mature forest in New England now than at any other time in history since the glaciers left," DeGraaf says.

Compounding the problem is the public's outcry against forest-management practices - such as clearcutting - that create such forest openings. The result? Early-successional habitat in the Northeast, DeGraaf says, "has evaporated off the landscape," and birds that are associated with shrub and grassland habitats are in steep decline. Among them are the eastern meadowlark, short-eared owl, vesper sparrow, brown thrasher, grasshopper sparrow, and others. "The rufous-sided towhee is the fastest-declining forest bird in Massachusetts," he says, "but if you tell that to someone in California they'd be very surprised."

If current trends continue, DeGraaf is hardly optimistic about the plight of these birds in the Northeast. "To see them now you have to go to the big airports," he says, where large open fields attract such species. "The state endangered list is just going to get longer with early-successional birds."

The Bottom Line

Forest researchers are increasingly convinced that ecosystem- and landscape-scale planning will be necessary to conserve avian biodiversity. The shortcomings of small forest fragments as nesting sites for a large number of songbirds only underscores the importance of large forested landscapes. How we protect and manage those landscapes will be critical, for just as certainly as society will demand wood products, society will also demand forests with a diverse array of flora and fauna. Most scientists agree that those are not inherently antithetical precepts. The key is balance.

It's important to maintain some landscapes that are extensively forested so predation and parasitism will be comparatively low. "By having these large blocks of continous forest," Thompson says, "we have the opportunity to manage for the variety of forest habitats required."

To do that, says Askins, "We need to simulate the kinds of disturbances - from beaver dams and fires to windstorms - that would have occurred naturally in the pre-settlement landscape. And there is a way to do that without having the entire landscape pockmarked with clearcuts." It would be better, he says, to zone a forested landscape with areas of bigger clearcuts in one zone and areas of unmanaged forest in another. Instead, says Thompson, "there is the tendency to want to do the same thing everywhere, so we decide we ought to do just selection cutting or we ought to do just clearcutting. But this does not mimic natural disturbance patterns."

That evolutionary process has involved a landscape with openings small and large. This we know from a reading of history, whose account provides a 20/20 perspective on the past. With the rising tide of concern about neotropical songbirds and a closer inspection of how timber harvest affects forest denizens, a similarly clear vision might guide management of our forests in the future. The result might be a renewed passion of the American love affair with wild birds, and a chorus of springtime birdsong no less rich in voices tomorrow than in years past.

RELATED ARTICLE: BREEDING BIRD SURVEY

Each spring volunteers with the U.S. Fish and Wildlife Service fan out across the North American continent. Armed only with clipboard, pencil, and an expert's knowledge of bird identification by sight and sound, these volunteers provide the only source of long-term population data available for all bird species on a continental and regional level: the U.S. Fish and Wildlife Service's Breeding Bird Survey.

The BBS, as it is known, began in 1966 as a means of tracking the population trends of all bird species found in the United States. Each spring, volunteers sign up to monitor birds seen and heard along pre-determined 24.5-mile of secondary roads. Beginning at one-half hour after sunrise, the volunteers stop every half-mile to look and listen for exactly three minutes, noting every bird seen or heard within a quarter-mile of the stop. After the three minutes are up, back into the car for a short dash to the next stop, where the process is repeated 50 times. It's all part of building one of the most impressive and important wildlife databases in the entire world, a database whose computer-generated statistics are used in wildlife research the world over.

There are 3,700 BBS routes in North America, and surveys take place in every state except Hawaii, plus Canada. In 1993 a three-year pilot program began in Mexico. For more information, and for details on how to volunteer, contact the Breeding Bird Survey, Patuxent Environmental Science Center, Laurel, MD 20708.

EDDIE NICKENS

RELATED ARTICLE: BYE-BYE BUNTINGS

Bird biologist Dr. Erick Greene of Missoula, Montana, hikes up the brushy slopes of Mount Sentinel each spring, carefully searching the ninebark and serviceberry shrubs for bird nests. He closes his eyes and listens to bird songs, hoping especially to hear the sweet warbling of the lazuli bunting.

Greene has a special interest in lazuli buntings. For the past two summers he and his students at the University of Montana have studied these birds near the college.

The buntings commonly nest along creeks and rivers throughout the western U.S., after wintering in Central or South America. They are so precise in their nesting calculations, Greene says, that each bird returns to its own bush each year.

He and his students have captured, banded, identified, and recorded the songs of 400 different lazuli buntings. Each bird's song is as individual as a fingerprint, allowing biologists to make an "acoustic fingerprint" - a computer song recording or sonogram that looks like sheet music - by which each individual bird can be positively identified.

Greene has become intimately involved in this bird species - and he's worried. His research shows lazuli-hunting numbers to be declining, he says, from predation by brown-headed cowbirds. According to historical data, cowbirds and lazuli buntings coexisted until relatively recently. The cowbirds followed bison on the Great Plains; the buntings lived in riparian habitat and western forests. But the forests are being logged, cleared for agriculture, and urbanized at a rapid pace, and this fragmentation is making it easy for predators such as cowbirds, raccoons, and house cats to find songbirds' open, cup-shaped nests.

Cowbird sightings in remote wilderness areas concern wildlife biologists because the bird will impact many other species of neotropical migrants. It will also affect management plans for forests and refuges. This past summer Greene and his students conducted radio telemetry studies on thousands of cowbirds in a communal roost on an island in the Clark Fork River at the base of Mount Jumbo and the north end of Mount Sentinel. He hopes to develop a management plan to help buntings hold their own against cowbirds.

His rationale for doing so is simple. "I am concerned that one day when I stand on my porch some May evening and listen for the songs of the beautiful lazuli buntings as they return to Missoula, I will hear none."

One effort that promises to prolong the song involves the group Partners in Flight. Launched in 1990 by the National Fish and Wildlife Foundation, this massive program crosses boundaries between government, industry, end nonprofits by teaming professional biologists, educators, and policymakers to develop and implement land-management strategies to help migratory birds. The goal is to improve understanding of neotropical migrants, identify species at risk, and develop cooperative strategies to protect habitat through conservation, wildlife management, professional training, and public education.

Partners in Flight's "Citizen's Guide to Migratory Bird Conservation" explains how individuals can help through efforts in their yards, in the field, and from their desks. This excellent booklet is available for $5 (five or more, $2 each) from the Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY 14850 or by calling 607/254-2440. - Jay Simons

RELATED ARTICLE: HOW TO HELP ON THE FORESTED FORTY

Stemming the decline in the numbers of many neotropical migrants may be a problem that spans hemispheres, but that doesn't mean the small-acreage landowner can't fit into the picture. Here are some suggestions for the landowner who wishes to turn a five- to 50-acre woodlot into an avifauna biodiversity bonanza. Or something like that:

* Landowners should first look at their ownership in the context of what is around them, says Richard DeGraaf of the USDA Forest Service. "If you own 10 acres and are surrounded by miles of forest that looks just like yours, do something different. Cut some of it. If you've got the only woodlot around, don't do anything." DeGraaf suggests a 10-to-1 ratio: A landowner with 25 acres should look at the surrounding 250 acres and see how his or her acreage fits in with the landscape.

* Landowners should set priorities, says Frank Thompson, also of the Forest Service. If they simply want to observe the widest variety of birds on their land and harvest timber, some form of group-selection cutting or small clearcuts will likely produce the greatest bird diversity. Woodlots with a few openings of three to five acres will host a lot of structural and habitat diversity. "But if you are really interested in the long-term viability of these birds," Thompson says, "you ought to get together with your neighbors and public land managers, and plan as a group how to manage your land, because you need to complement one another to meet the needs of habitat-interior or edge-sensitive wildlife, early-successional wildlife or late-successional wildlife."

* University of Wisconsin professor Craig Lorimer points to specific actions that can increase bird diversity in a given woodlot. Planting idle fields in trees will increase the suitability of adjacent woodlots for most neotropical migrants, especially in agricultural areas. Maintaining mature forest cover along floodplains and small streams in the central and eastern oak-hickory forests will benefit declining species such as the cerulean warbler, hooded warbler, prothonotary warbler, and Acadian flycatcher. And bird diversity in a hardwood stand will be increased by planting small- and medium-sized patches of coniferous trees. - EDDIE NICKENS

EDDIE NICKENS - writes on environmental concerns from his home in Raleigh, North Carolina. The author would like to thank Dr. Craig Lorimer for his specific direction and assistance with this article.