A Tale of Two Habitats: Vermont
Each spring thousands of migrating wood thrushes fill the eastern forests of the United States with the reedy tunes of vitality and new notes of uncertainty.
In late spring the hillside forest along Thatcher Brook in the central Vermont town of Granville is damp and dark: damp from the bubbling tumble of water over rocks, and dark where the brook has driven a tunnel through the tangle of underbrush and beneath a climactic canopy of hemlocks and broad-leaved trees. A passing hiker breathes in a heavy odor of decaying leaf litter. Yet even over the brook’s turbulence, he detects a kind of spirit voice. It is a three-part rhapsody, beginning with two or three low notes, then a series of louder, flutelike phrases, and finally a haunting trill. Sometimes only a reedy ee-oh-lay overrides the stream’s liquid monody.
Henry David Thoreau heard the wood thrush’s song in a distant century and in another part of New England when he mused, “The thrush alone declares the immortal wealth and vigor that is in the forest.” So the notes are a part of our country’s literature, as well as of the individual memory of our hiker, for whom it summons up other woodland scenes and thrushes from past springs. But the melody isn’t directed at us. It is sung by the male thrush to identify himself and define his territory against the possible encroachments of other thrushes or, if he is in need of a mate, to state his case.
The wood thrush’s muted tune portends troublesome change for 200 neotropical songbirds that travel hundreds and thousands of miles twice every year to winter in Central America and the Caribbean and breed in North American forests. They are literally birds of two worlds, and their spheres are shrinking. Tropical wintering grounds have been logged for valuable hardwoods, burnt and cleared to make way for farmlands, and tapped by modern-day oil tycoons seeking to liquidate forests by siphoning whatever fuel they might harbor (see “A Tale of Two Habitats: Belize”).
Here in the north, where the wood thrush’s range covers the eastern half of the United States and adjoining Canada, large blocks of forest have been dismembered and replaced by industrial parks, shopping malls, busy roadways, and housing developments. In many places only wooded remnants, small and isolated, are left, and they are unable to sustain healthy, diverse wildlife populations. At the same time vast acreage belonging to an aging human population may soon change hands and shred the fabric of the forest itself. These dire circumstances have spurred landowners, non-profit organizations, and professional foresters to join forces in hopes of preserving the woodland soundtrack of warbles, twitters, and trills sung by winged migrants like the wood thrush.
“Among all the migrants, the wood thrush is particularly worrisome to us,” says Greg Butcher, National Audubon’s director of bird conservation. “Some forest species seem to be holding their own; others, such as cerulean warblers and rusty blackbirds, are showing big declines. But the wood thrush, the most widespread of our eastern forest neotropical migrant species, is declining at an estimated rate of 1.8 percent a year in North America—which brings the population down to 14 million individuals, about 48 percent of what it was 40 years ago.”
Modern bird banding has shown that for wood thrushes wintering in Central America, Vermont’s extensive woodlands are a big target on their northward migration in spring. They take off from the tropics in a continuous stream through much of March and April and head northward over the Gulf of Mexico, then fan out across the eastern half of the United States and into southern Canada. Winging by night, they avoid encounters with day-flying hawks, and take advantage of lighter winds and cooler temperatures. Butcher estimates that depending on how far south in the tropics wood thrushes winter and how far north they breed, they will travel anywhere from 300 to 3,000 miles.
Generally arriving on the mating grounds at least several days before the females, the males are in full dress: rusty plumage about the crown and nape, with olive-brown back and wings, and a spattering of big dark spots on the chest and sides that help to obscure their trim shapes from predators. The coloring blends subtly with this species’ prime nesting habitat—the dense inner deciduous or mixed forest that French Impressionist painters called the sous bois, where thick foliage filters the sun and creates patterns of dappled light and shadow in the understory. Here the soil is often damp under decaying leaf litter.
Upon her arrival, the female builds a cup nest similar to a robin’s, usually in the lower branches of a broad-leaved tree. She works with plant material and mud, lining the hollow round with rootlets and inserting here and there bits of white paper, cloth, and other trash—the gleaming whiteness apparently breaking the nest’s contours and adding a touch of mottled yet concealing coloration.
Small prey is everywhere in the shadows. Beetles, spiders, millipedes are easy pickings. The birds hop over the uneven forest floor on long, pink-tinged legs, probing soft places or tossing over a dead leaf with quick thrusts of their slender bills. In this ideal setting a mated pair has a fair chance of protecting the usual three or four greenish-blue eggs in its clutch and rearing at least a couple of the chicks to the fledgling stage. Fed and fattened on a protein-rich diet of insects and other small invertebrates, the young birds will leave the nest in about two weeks and begin life on their own.
Forest fragmentation, however, turns the odds against thrushes and other neotropical migrants. Splintered forests do not often provide the dense interior canopy under which thrushes find the flourishing insect populations they need to successfully rear their chicks. Consisting disproportionately of tattered edges, fragments also give easy access to raccoons, chipmunks, domestic cats, crows, and blue jays—insatiable predators on songbird nests. Other ill-fated birds may encounter cowbirds, brood parasites that often lay their own eggs in the nests of migrants. However, these freeloaders are less prevalent in Vermont and nearby states than in the Midwest, where they seriously reduce the breeding success of ground-nesting birds.
Biologists are also revealing an insidious threat to the wood thrush and other species from acid rain. Pollutants, including sulfur oxides and nitrogen oxides, released by motor vehicles and coal-fired power plants, mix with water vapor in the atmosphere. The moisture eventually falls as rain or snow, heavily laced with contaminants that can have a rippling effect in the forest food chain.
Stefan Hames at Cornell’s Laboratory of Ornithology and his colleagues have shown that chemical reactions to acid rain leach calcium from forest soils, leading to a decline in calcium-rich invertebrates, such as millipedes and snails. Birds that prey on these animals, including wood thrushes, thus lose a source of the key ingredient in making eggshells, the scientists theorize. In a further intriguing twist, researchers were less likely to find the wood thrush in areas poor in calcium. Hames and his colleagues report that among several thrushes studied in the Northeast, “the wood thrush takes millipedes as prey, in addition to being the species showing the greatest decline.”
Acid rain also frees up heavy metals and deposits other toxic substances. Among the worst of them is mercury, which biologists have found in certain abundant species on the forest floor, including wolf spiders.
“It’s important to remember that we are looking at multiple threats to the wood thrush in its breeding habitat,” Hames says. “We want to know more about the properties of forest soils and invertebrates. We believe substances like mercury are pushing the forest in a direction it probably doesn’t want to go.”
In a nation whose settlement and expansion depended so mightily on the ability of its pioneers to clear forests with remorseless efficiency, it hasn’t been easy to get across the notion that trees are for living with. In his acclaimed 2006 book, The Tree, Colin Tudge offered the minimalist definition of his subject as “a big plant with a stick up the middle.” Robert Frost revealed the tree at his window as a “Vague dream-head lifted out of the ground/And thing next most diffuse to cloud.” But the wood thrush sees it from a survivor’s point of view: a spruce for sheltering under, a sugar maple for nesting in, a paper birch for singing on. In total, the thrush’s trees compose a healthy ecosystem.
Forests cover nearly eight out of every 10 acres in Vermont. Unlike most states in the American West, where vast expanses of woodlands receive protection of varying degrees in federal holdings such as national parks and forests, only about 14 percent of Vermont’s 4.6 million wooded acres are in federal, state, or municipal ownership. Farmers, corporations, and the forest industry control more than 20 percent of timberlands. Private individuals own 63 percent, with holdings mostly ranging between 100 and 500 acres.
Yet Vermont’s landowners form a demographically unstable group of organizations and individuals. According to the Manomet Center for Conservation Sciences in Massachusetts, 23.8 million acres—or 85 percent of the forest in northern New England—changed hands between 1980 and 2005. The forest products industry once controlled much of the region’s undeveloped land and managed it for short- and long-term financial returns. Some new owners, however, are investment corporations interested in quick profits and rapid turnover—meaning subdivision after they log the timber. Many of the individual landholders are older men and women, on the far side of 60, who are facing escalating taxes and lack the considerable wealth needed to keep their holdings intact without some assistance. With the not-too-distant passing of this generation of owners, Vermont’s forests are approaching an unprecedented crisis.
Richard Hotchkin stands alongside the Vermont landowners concerned about the future of forests and wildlife in the north. He divides his time between his A-frame chalet over Thatcher Brook in Granville, and Braintree, Massachusetts, 120 miles away, where he serves as pastor of the 301-year-old First Congregational Church. “Pastor Dick,” as his congregants call him, is 61 years old, a tall slender man with white hair and a long ascetic face that might not be out of place on one of the portals holding sculptured figures at Chartres Cathedral. Yet before he received his call to the ministry in 1989, he worked in big industry’s turbulent world. A graduate of the University of Michigan School of Law, he was general counsel for an international coal refining company and, before that, a senior
attorney for a major chemical company.
“I spent very little time thinking about land preservation,” he admits. “Now I see the world differently, especially since my wife, Toni, and I purchased our mountain forest. There is no doubt I’ve been influenced by the Bible and the writings of Aldo Leopold and Wendell Berry. I have come to realize that we human beings are part of something much larger than ourselves.”
The couple bought 228 forested acres in 2003. They look down from their rustic chalet on a jungly canopy formed over the brook by leaning hardwoods and a scattering of hemlocks. Although the dense trees and flow of water drown out the song of a resident wood thrush in spring, Hotchkin takes solace knowing that it’s there from his wanderings in the woods.
The message he delivers to his congregation in Braintree, both from the pulpit and in informal conversations, is steeped heavily in his faith. “When I walk in our mountain forest I do not see creation as something that happened at some long-forgotten moment in time,” he tells his listeners. “I see God continuing to be very much involved in creation—actively bringing order out of chaos, light out of darkness, and hope out of despair.”
The Hotchkins’ Granville neighbors are Peter and Julie Parker. The couple, now in their 70s, share with Pastor Dick a concern for the forest but come to it from a more utilitarian interest. Since meeting as students at Middlebury College in Vermont, business, particularly dealings associated with forestry and wood products, has taken them across the country. Peter Parker inherited pine timberlands in Mississippi from his father and later bought 2,300 acres of cutover coastal redwoods in California (where the couple now lives for part of the year). Both families have a strong interest in sustainable forestry, keeping their land ecologically and commercially viable. They are able to afford to protect large acreage (the Parkers own 550 acres, at elevations from 1,600 to 2,500 feet) if there is what they call a “stewardship return.”
“We try to add to the value of our property so that in the future, whoever owns it will want to keep it intact,” Parker says. “The land, in part, must pay for itself. If it stays ‘forever wild,’ will there be anyone who wants it, or who will be able to keep it as it is?”
The Hotchkins and the Parkers, like many other present-day Vermonters, have retained a professional forester to help them develop plans for cutting timber at a rate that will continue to maintain wildlife while keeping the forest’s aesthetic values intact. Hotchkin heard about Audubon Vermont’s Forest Bird Initiative, and in 2006 he attended a meeting organized for foresters and landowners. He learned that Audubon biologists survey forested properties to identify and monitor resident birds and pinpoint habitats important to them.
Afterward Hotchkin sought the expertise of Steve Hagenbuch, a conservation biologist with Audubon Vermont, who has visited 38 plots of land, from 30 to 3,000 acres, advising the owners on how to manage forests that provide homes to breeding neotropical migrants and other birds.
Securing adjacent properties across the state is one way of protecting large forest blocks. Hagenbuch often advises landowners to make a small number of up to two-acre patch-cuts (small clear-cuts), allowing the regrowth of those areas to promote a denser understory and the maturation of saplings. This strategy helps create a natural multi-layered assortment of forest that can support a greater variety of species. To maintain bird habitat within the clear-cut areas until the forest begins to reclaim the understory, he suggests leaving some standing trees, both live and dead, as well as six standing snags an acre.
“When I first started out, I wanted all wilderness,” Hagenbuch recalls. “Now I recognize that those patches provide habitat for certain species of wildlife, even bears that come to feed on regenerating berry plants. We look for a mosaic of different-aged stands—providing diversity.” For example, despite having logged about 80 percent of their land since 1981, the Parkers maintain a healthy, diversified forest that is prime wildlife habitat.
Another statewide nonprofit group that landowners are increasingly turning to is Vermont Family Forests (VFF). Its founder, David Brynn, expresses VFF’s approach: “It’s our job to manage human actions so they respect the forest’s capacity for self-renewal.” The organization’s programs allow landowners to “green certify” their land and find markets where they can sell their products, much as food growers earn organic status for their produce.
Those who sign an agreement with VFF to follow sound forestry practices then get help in planning to meet the requirements of an independent certifier, the Forest Stewardship Council. The plan that owners must submit to VFF specifies access roads, buffers along streams, and data to identify fragile natural communities. Landowners may sell their certified wood at auction. It’s not big business—most landowners don’t really keep good records, and the profits range from as little $16 an acre up to $50 an acre. Still, the approach has been precedent setting, says Brynn. Putting a conscientious landowner, rather than a logger or a mill, in the driver’s seat has encouraged at least three other states—Washington, Massachusetts, and Wisconsin—to emulate the VFF roadmap.
In mid-August, as daylight shortens, restlessness stirs through Vermont’s wood thrushes. The birds seek out forest openings where berry bushes—blueberries, elderberries, wild cherries—have grown up from the forest floor. Switching now from the protein-rich insects of the breeding season, they fatten on fruit to store energy for the long flight that lies ahead.
They leave the northern forest, a few at a time, joining the millions of other neotropical migrants on their annual southward migration. Making their way on a broad front without a well-defined route or schedule, they travel in stages. When the tailwinds blow and the night skies are clear, the thrushes fly for maybe a few hundred miles at a time, then stop for as long as several days to refuel their metabolic gas tanks before their next dash. “Essentially every woodlot in the eastern half of the U.S. (including New York’s Central Park) is a stopover site for migrating thrushes,” says renowned naturalist and bird guide author Kenn Kaufman. “When they’re going across open water, they’ll make longer flights covering a greater distance.”
For that reason, one popular pit stop—especially in foul weather—is along the Gulf Coast, where the thrushes may forage for the last time on North American soil. With a break in the night sky, they are on the wing again, each a couple of ounces of fluff over the heaving Gulf, and on to new hazards in Central America’s forests.
To read about the wood thrush's wintering grounds in Belize, click here.
To hear the call of a wood thrush, click here.
WHAT YOU CAN DO
The most challenging threat to wood thrush breeding in the eastern United States is human development, which not only carves up forests but leaves breeding wood thrushes vulnerable to predators and nest parasites like cowbirds. Audubon’s Important Bird Area program works to identify and preserve woodlands vital to wood thrushes and other species. The Cornell Laboratory of Ornithology and the U.S. Forest Service coordinate a citizen-science project called Birds in Forested Landscapes, linking volunteer birders with professional ornithologists in a study of the habitat requirements of North American forest birds, including the wood thrush.
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