(backyard)

Rest Stops for the Weary

When you've flown 600 miles without a break, a backyard full of native plants is a welcome sight indeed.

by Janet Marinelli

It isn't really spring in my yard until the palm warblers arrive. These pint-size songbirds with streaked breasts, bright olive rumps, and rufous caps are among the first migrants to find their way to my garden on Shelter Island, New York. Come April, they flit from branch to branch in the thicket of shrubs, young wild cherry and sassafras trees, and wild grape vines that edge the small moss lawn behind the house, feeding on tiny caterpillars and other emerging insects. In a few days they're gone, replaced by yellow-rumped warblers, black-and-white warblers, and various vireos, flycatchers, and thrushes.

I've been known to complain about the two-and-a-half-hour drive from my Manhattan apartment to my family's summer cottage on Shelter Island. But at least I know where I can stop for some comfort food when I've had my fill of the road rage on the Long Island Expressway. Alas, that's not the case for migrating songbirds. The rigors of migration leave them in unfamiliar landscapes when they're close to their physiological limits. They don't have the luxury of seeking a better meal or a place to rest.

Every spring millions of migrants fly 600 miles or more from the Yucatan Peninsula clear across the Gulf of Mexico. The avian voyagers proceed in waves up through the East, Midwest, and Plains states. Many continue to the vast coniferous forests of Canada, or as far north as the Arctic. Species that breed in the western states, including the endangered southwestern willow flycatcher, may have to fly for hours over inhospitable terrain in the Chihuahuan Desert before they can find refuge in the relatively lush vegetation of bosques along the middle Rio Grande. And since the 1950s these biannual migratory marathons have become even more of a challenge: Vast stretches of natural habitat along North America's major coastal and inland migration routes have been carved up and developed, contributing to the decline of some songbird species.

Much of what is recommended as "landscaping for birds" ends up helping blue jays, chickadees, and other species that flourish in the scattered trees and turf typical of suburbia. But we can do more, transforming our backyards into bed-and-breakfasts for migrants and easing the plight of warblers, vireos, thrushes, and other threatened songbirds.

To ensure that they reach their breeding or wintering grounds alive, migrants must put on enormous amounts of fat. A blackpoll warbler, for example, which breeds in Canada, can almost double its weight, ballooning from about 12 grams (half an ounce) to more than 20 grams. The extra fat makes it possible for the tiny bird to fly nonstop between the New England coast and the north coast of South America. But most songbirds can't accumulate enough fat to make their trips in one continuous flight; they need to stop several times to rest and refuel. They depend on finding suitable "stopover" habitats, places with an abundant supply of emerging insects in spring and fruits and bugs in fall.

The tiniest of all migrating birds are hummingbirds. In spring, three-inch-long ruby-throated hummingbirds, which spend the winter as far south as Panama, begin the long flight across the Gulf of Mexico, making landfall in the southeastern states. Many continue up into southeastern Canada. Rufous hummingbirds, which winter in Mexico, move through the Pacific lowlands to nest as far north as Alaska--farther north than any other hummer. Hummingbirds look for both bugs and nectar from tube-shaped flowers.

If high-quality habitat is not available, even exhausted and emaciated migratory birds must continue until they find adequate food and cover. If they're too thin or weak to continue, they'll either starve or succumb to predators. It's estimated that half of all migrants heading south for the winter won't return to breed in spring.

Scientists who study songbird population declines have devoted most of their time to investigating losses of nesting and winter habitat. Until quite recently, stopover habitat received scant attention. However, according to the small but growing cadre of stopover ecologists, even small patches of stopover habitat can mean the difference between successful migration and starvation for many species. In one study, biologists compared the migrants' use of large, continuous bands of streamside vegetation with the use of fragmented habitat islands, less than two and a half miles long, in southeast Arizona. They found that migrating birds in need of refueling used the isolated patches as much as the larger corridors, if not more. Other studies have demonstrated that shelterbelts--long, narrow plantings of trees and shrubs first promoted in the mid-1930s to reduce soil erosion--are important stopover habitats in the Plains states. After reviewing the existing research on habitat needs during migration, another group of scientists concluded that even habitat islands in the middle of urban and agricultural landscapes can provide much-needed stopping places for famished songbirds.

In our own yards, we can make life easier for migrating land birds by providing areas with as many of the different layers of plants found in a healthy forest as possible: the tallest trees that form its roof or ceiling, smaller understory trees, shrubs, and groundcovers. Vines often connect the various vertical layers, clambering up bushes and high into the trees. Landscapes with all these layers, especially shrubs loaded with berries, are magnets for migrating songbirds. Because these shrubs appeal to people, too, "gardens can often provide good stopover habitat," says Robert Askins, a biologist at Connecticut College and the author of Restoring North America's Birds.

The goal is to re-create the gamut of habitat niches preferred by different species. Evidence suggests that migrant songbirds aren't fussy about vegetation type, the particular species that make up a plant community--an oak and hickory forest, say, or a boreal forest of spruces and firs. Blackburnian warblers, for example, breed in the coniferous forests of Canada but feed in deciduous forests while migrating through most of the United States. However, migrant songbirds are more particular about vegetation structure and vertical layers: The mourning warbler has a definite affinity for shrubby thickets, whereas the magnolia warbler favors both tall and understory trees. Two-thirds of all the migrants observed in one study were found in shrubs and understory trees--the layers most often missing in the typical suburban landscape.

Whether your property is a small city lot or a vast estate, concentrate on restoring these vertical layers. If you live in the East, South, Midwest, or Plains states and there are tall trees on your property, plant understory trees--dogwoods are among the best. Fill in the gaps with shrubs, the more different types the better. Many migrants are attracted to thickets, dense masses of fruiting shrubs, vines, briers, and brambles. Native trees and shrubs are best, because they are genetically programmed to leaf out, bloom, and fruit at precisely the right time for the migrants with which they've co-evolved. Along the edges of your stopover garden, plant shrubs with lots of fall fruit, as well as clumps of nectar-rich flowers for hummingbirds. For specific recommendations, see "Furnishing a Backyard B & B," at right. And while you're at it, include some milkweeds and goldenrods, favored plants of migrating monarch butterflies.

If there are no tall trees in your yard, consider planting a songbird hedge or hedgerow. I'm not talking about a formal (and backbreaking) hedge that needs to be clipped as meticulously as a poodle, but rather a spectacular mixture of flowering and evergreen trees and shrubs left to follow their own growth habits. As recently as 60 years ago, fields and pastures bordered by hedgerows dominated the landscape in the eastern two-thirds of the country. Mature hedgerows typically included some canopy species, along with beautiful understory trees and shrubs such as native viburnums. Songbirds flourished in this environment. Unfortunately, hedges and hedgerows have been replaced in communities across the country with warrens of wooden stockade fences that are uninviting to birds as well as next-door neighbors.

To create a hedge or hedgerow, plant the center or tallest part first, with a few scattered oak, tulip, or other canopy trees; consider buying the more natural clump forms rather than the standard single-trunk, shade-tree forms. On either side and among the taller species, plant flowering and evergreen understory trees. After all the trees are installed, add a diverse mixture of fruiting shrubs and a vine or two; finally, include nectar plants for the hummingbirds and butterflies. If your property is small, leave out the largest trees and choose the more compact varieties of understory trees and shrubs.

In the western states, streamsides and washes are by far the most important habitats for migrating and breeding birds alike. Yet these are among the most threatened habitats in North America--more than 95 percent of the riparian habitat in the western United States has been destroyed or degraded, according to Askins. Gardeners and landowners have a major role to play in the restoration of critical floodplain habitats.

To restore a floodplain, re-create the series of ascending zones or terraces found in these habitats, because different sets of birds use the different areas. Closest to the water is the first terrace, covered with a tall, multilayered woodland of cottonwoods and willows frequented by willow flycatchers and yellow warblers, among others. Plant this zone densely with a mixture of trees and shrubs. As the ground rises, make the plantings more scattered, as is typical of upland areas. Black-tailed gnatcatchers and Lucy's warblers are just two of the songbirds that use this type of open woodland. In the Southwest, mesquite, wolfberry, saltbush, and other plants that prefer drier soil grow on upper terraces. The particular collection of species varies somewhat by region and elevation, so look for those that are native to your area and situation. Try to use at least three different species and ideally more than seven. For recommendations, see "Furnishing a Backyard B & B."

After the planning and the planting, your stopover garden will require very little work. In return for the initial effort, you'll get a great deal of pleasure. Each spring and fall, you'll look forward to the succession of beautiful flowers and fruits, as I do in my Shelter Island garden. The birds arriving in your backyard stopover habitat will seem like old friends. Best of all, you'll be making migration a little less perilous for these songbirds on the move.

Janet Marinelli is director of publishing at the Brooklyn Botanic Garden and the author of several books on ecological design, most recently Stalking the Wild Amaranth: Gardening in the Age of Extinction.

© 2001  NASI

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