>Bird Conservation

Living on the Edges

Across the country, researchers who are studying sprawl's impact on birds are concluding that if you can't beat it, plan it. So they are designing landscapes to help, not hurt, native species.

By T. Edward Nickens / Photography by Mitch Epstein

The Crabtree Valley Mall in Raleigh, North Carolina, houses more than 220 retailers. The birds most comfortable in the slim greenway abutting it are "urban adapters," such as European starlings.

On a mid-May morning, summer and scarlet tanagers throng Black Creek's canopy of tulip poplar and swamp chestnut oak. Gorging on caterpillars, the brilliant red migrants are joined by mixed flocks of orchard orioles, cedar waxwings, black-throated blue warblers, and northern parulas. Each bird is in full song—warblers sparring for nesting space, flycatchers chattering as if boasting over their latest aerial feat. It's the sunrise chorus that birdwatchers yearn for each spring, but this one is scored with a jarring percussion section. A car door slams shut, cutting off a summer tanager in husky mid-carol. Air-conditioner compressors drone over the cheery whistle of a Louisiana waterthrush. Human voices, highway noise, a high school band tuning up for early morning practice—amid the year's most impressive display of birdsong, a disharmony of suburban clatters and honks.

Leaning against an ironwood tree a few feet from the stream, Christopher Moorman isn't surprised. A wildlife ecologist at North Carolina State University, he carefully notes the species and location of each bird that sings or wings within a 50-foot radius. "Clearly, Black Creek is an oasis for birds," he whispers. But Black Creek flows through a tidy neighborhood in Cary, North Carolina, one of the nation's fastest growing towns. The paved greenway trail beside the creek is beloved by hikers, bikers, dog walkers, families on picnics, and children on Rollerblades. Backyards crowd the woods. "The problem," Moorman says, "is that it's an oasis for humans, as well."

Greenways and parks have long been attractive to humans seeking respite from the pressures of city and suburb. Now Moorman and his collaborators are trying to learn if the Black Creek greenway is a healthy place for birds, and if there are ways to make it better. Across the country, in fact, a growing number of researchers are posing pointed questions about how birds are affected by sprawling cities and suburbs, and how various open-space designs—parks, linear greenways, large buffer zones between town and countryside—function as bird habitat.

For years, explains John Marzluff, a wildlife ecologist at the University of Washington in Seattle, large intact natural areas were regarded as the primary targets for bird conservation, while urban spaces and the suburban fringe were rarely considered. "Now we're beginning to understand how birds fare in human-dominated ecosystems," he says. "These are new challenges, because these places are vastly different from the pristine environments most scientists have studied."

In North Carolina the focus is on greenways. These long, linear strips of woodlands, mostly sited along streams, have been developed in more than 500 North American cities. Lauded as a national leader in greenway planning, Cary and its next-door neighbor, the state capital of Raleigh, boast more than 50 miles of greenways, with plans for large-scale expansion. Such wooded corridors are frequently touted for providing much-needed wildlife habitat in developed landscapes, Moorman says, "but we don't know if it's good habitat, because we don't know what's happening to the birds that use it." In addition, there is very little direction available for urban planners who would like to boost a greenway's attractiveness to migrating and breeding birds. "Right now all people hear is that wider greenways are better than narrow ones," Moorman points out. "But what does wider mean?" He's not sure whether it's 250 feet to 700 feet, or wider. "That kind of ambiguity drives developers and land-use planners crazy," he explains. "We're working to refine those suggestions."

 

Moorman and his collaborators, including a landscape ecologist, an urban planner, and a parks and recreation expert, are studying how songbirds fare in small fragments of land cover surrounded by neighborhoods, shopping centers, and industrial areas. Scientists know of the troubling consequences that befall native birds when logging pocks forests or agricultural use chops woodlands, prairie, or desert into ever-smaller pieces. They call them "edge effects"—increased competition with nonnative species, greater exposure to predators, and restricted travel corridors. The North Carolina researchers want to learn how migrating and breeding birds respond to such habitat fragmentation in an urban environment, and they're looking at two factors under the direct control of planners and developers: greenway width and the intensity of development on adjacent lands.

In many places the Black Creek greenway is wider than a football field, filled with mature hardwoods, nodding ferns, and blooming trilliums and false Solomon's seal. But other Cary and Raleigh greenways are whisker-thin, with town homes and manicured backyards cleared to the creek banks. Last year Moorman's graduate students monitored bird use of 34 greenway segments—some wide, some narrow, some adjacent to chockablock apartment buildings, others coursing through low-density suburban neighborhoods and even commercial districts. They counted tracks in dozens of handmade, carefully groomed circles of sand that were baited with fox urine to attract predators such as raccoons, opossums, and domestic dogs and cats. They wired artificial bird nests to remote cameras to identify animals that preyed on birds' eggs. Other students tabulated the presence of exotic plant species; how many greenway users were walking, running, biking, or using Rollerblades; and whether pets were leashed or running free.

Their early findings aren't encouraging. So far the research shows that high-density housing developments have such minimal forest canopy that there's little chance for some native bird species to sustain themselves in any but the widest greenways. Native North Carolina breeding species such as ovenbirds, scarlet tanagers, and white-eyed vireos weren't encountered a single time in the narrow greenways. Even parcels up to 1,000 feet wide, the scientists learned, are likely not large enough to provide adequate breeding habitat for all native birds.

Arthur Morris/Birds as Art (4)

Gaining the Upper Wing When a natural landscape is carved into smaller, more isolated patches, some species gain a competitive advantage, says Christopher Moorman, a wildlife ecologist at North Carolina State University. Other species are dealt a competitive blow. Take the black-and-white warbler, a forest dweller that lives entirely on insects. Among the greenways of fast-growing Cary and Raleigh, North Carolina, this once familiar migrant is now found nesting in only the widest bands. By contrast, even the region's narrowest woodland corridors contain the common grackle, a species that eats everything from grain and grubs to goldfish. In the open space surrounding Boulder, Colorado, grassland species such as the savannah sparrow are far less concentrated near the urban edge. Meanwhile, birds that are well adapted to human development, like the American robin, are moving into those areas. Changes in sunlight, noise, food, shelter, and predation can all affect species' chances of survival. The challenge lies in balancing the odds. —Carolyn Shea

But the research also suggests that there is an opportunity for greenways to give birds a hand. The natural areas serve as critical "stopover habitat," in which migrating birds ravenously feed to replenish depleted fat reserves. At times, chestnut-sided warblers, blackpoll warblers, and black-throated blue warblers flooded the greenways, even though these birds are not known to nest in the area. "These strips of woodlands are all the birds have left in many of these urbanizing environments,"Moorman says. "We can suggest better ways for developers and urban planners to boost their value for birds."

Recreational trail design is one instance in which there are lessons to be gleaned. Moorman says the team's most important finding was that wide, maintained paths and landscaped areas within the greenways "are bad news for birds." Break up a 1,000-foot-wide greenway with a 30-foot-wide walking trail and mowed shoulder, and you don't have a 1,000-foot-wide greenway any longer. You have two greenways that are not quite 500 feet wide. "This is something greenway planners can easily prevent," he insists, "and with public education, it's something greenway users should support." Also, since greenways less than 150 feet wide proved to be a wasteland for some deep-woods-nesting neotropical migrants, that could be considered a minimum size.

Developers also have the opportunity to craft more bird-friendly spaces. Many residential areas are designed with straight lines of grassy lawns and hedges—often planted in nonnative species—along the border between neighborhoods and natural areas. These abrupt edges leave a meager transition zone for birds to use as escape cover from predators such as hawks and cats. Adding insult to injury, Moorman explains, is that many greenway areas are shorn of shrubs and small trees. "That leaves big trees and turf, with no intermediate vegetation, and that's not much good for birds no matter how wide a greenway may be," he says. Replicating natural cover as closely as possible, with shrubs and trees of varying heights, increases nesting and foraging habitats. "Greenways can be made better," insists George Hess, a landscape ecologist on the project. "It's a matter of making choices that help birds, not harm them."

 

Making the right choices may mean moving in new directions. Even places known for anti-sprawl policies are facing unforeseen challenges. In Colorado, along the eastern foot of the Rocky Mountains, the city of Boulder has spent more than $150 million since 1967 acquiring open space around its urban core. The city's belt of grassland preserves and working hayfields is, per capita, the largest municipally owned open-space system in the country—roughly 30,000 acres—and is home to breeding populations of bobolinks, western meadowlarks, and vesper and savannah sparrows. But growing evidence suggests that only the interior portions of Boulder's grasslands are doing prairie birds much good. "Almost all our native birds are showing an aversion to the edges between the grasslands and the neighborhoods," reports Carl Bock, a biologist at the University of Colorado.

Bock and his graduate students have spent hundreds of hours observing birds in Boulder's grasslands. They baited dozens of artificial nests with quail and fake clay eggs. (Drawn to the quail eggs, predators mark the clay eggs with identifiable impressions of tooth, claw, or beak.) And they learned that grassland birds have good reason to avoid the urban edge. For starters, Boulder's neighborhoods harbor a voracious suite of predators—domestic cats, raccoons, skunks, crows, magpies, and others—that thrive in backyards and vacant lots and hunt the grassland margins, to the serious detriment of natives. These indigenous birds appear to be taking a hit as deep as 300 feet into the open spaces.

In addition, large populations of birds that don't typically occur in the region have set up housekeeping in Boulder's neighborhoods and are foraging extensively in its surrounding grasslands. Bock dubbed the most numerous of these—the American robin, European starling, common grackle, house sparrow, and house finch—the Suburban Gang of Five, and believes they may be outcompeting grassland birds at the suburban edges. "Grasslands don't support high bird densities like a forest does," he explains. "It doesn't take many outsiders to have a real swamping effect." Around Boulder there are outsiders aplenty. In fact, the Suburban Gang of Five comprised a whopping 30 percent of all bird sightings in the open-space grasslands.

From Colorado's grasslands to California's coastal chaparral suburbs and Florida's gated pinelands communities, urbanization "is wiping out unique birds and replacing them with über birds that can live anywhere," says Robert Blair, a conservation biologist at the University of Minnesota. An abundance of birds do wind up in developed landscapes, but that doesn't necessarily imply a balanced ecosystem. If you want to see "buckets of birds," Blair suggests, go to a golf course. What you won't see are forest and grassland birds, whose declining numbers have conservationists wringing their hands.

Those species require expansive areas, not pocket parks. Tough choices will have to be made. "Given limited resources," Bock says, "we need to stop fighting for every little piece of open space at the urban fringe and look to larger, more affordable land parcels away from the urban edge."

 

If the research has revealed any guiding principle, it's that there are few one-size-fits-all solutions. "We've already learned that some of the things we thought were true are not," says the University of Washington's Marzluff. For instance, "the whole impetus for managing growth through urban growth boundaries was to preserve nature," he says. But he has found there are unintended consequences of even that strategy.

By color-banding and tracking hundreds of birds, Marzluff and his students learned that native species such as chickadees, red-breasted nuthatches, and many woodpeckers actually can thrive in a landscape of natural cover interspersed with human development. "And that goes square in the face of what we've always heard," he says. But other kinds of birds—pileated woodpeckers, brown creepers, and red-breasted sapsuckers, for instance—lose out when humans move in. A diversity of development will promote a diversity of birds, says Marzluff. "We shouldn't do the same thing the same way everywhere."

This view may run contrary to current schools of thought. Across much of the West, development isn't characterized by expanding cities but occurs in distant rural regions. It's been argued, says Bock, that keeping ranchers from selling off their lands to developers is vital to conservation. He recently began a study at the National Audubon Society's 8,000-acre Appleton-Whittell Research Ranch (see "Fire in the Sky") to look at what happens to grassland biodiversity when large cattle ranches are lost to subdivisions. What is better for native birds, insects, rodents, and plants—a landscape that has been altered by widespread livestock grazing, or a carefully planned ranchland development with clustered housing and large grassland preserves? Bock intends to find out.

As of now, parks and greenways "are designed first and foremost with people and dollars in mind," Marzluff says. Researchers can't do much about urban sprawl; the economic and societal pressures to grow are too great. But they can suggest ways to build more wildlife-friendly cities, to arrange the landscape to conserve nature and benefit birds. To that end, everyone plays a role: Urban planners have the opportunity to site walking and biking trails along the edges of open spaces, instead of encouraging humans to penetrate deep into open lands. Developers have the choice of designing neighborhoods with as much natural cover as possible, leaving dead trees in places where they pose no threat to human life. And individual landowners can minimize all the nasty things that venture into greenways and urban parks, from kids with BB guns to cats to lawn trimmings filled with nonnative plants. "Can we compensate for habitats we're losing by treating the ones we have left in a better fashion?" asks Bock. He says yes. "It's where we need to go."

T. Edward Nickens wrote "Saving Our Bald Spots," in the September 2002 Audubon.