Land Use: A Bird's-Eye View

A look at the bird life of the Twin Cities region provides valuable insights for development decisions.

By Kim Alan Chapman

Every spring we get a migrating thrush - hermit, Swainson's, or gray-cheeked - in our St. Paul back yard. For a few days, its flutelike song seems to carry the fragrance of cedar and lake water to our door.

Later, near the end of June, I love waking up at 4 a.m. and lying in bed to listen to the urban choristers. First comes the robin, mouth open and shouting. Half an hour later, the cardinal throws his what-cheer? what-cheer? against the blue jay's yammer. Then an American crow raucously announces it's awake, while the mourning dove rises with graceful cooing. Grackles and house finches follow in short order. The house sparrow begins a dreary cheep-cheep-cheep, and the black-capped chickadee lets loose an indignant scold. Finally, under full sun, the twitters of chimney swifts collide with a bursting peek! of a downy woodpecker.

While I lie there hoping for a goldfinch's roller-coaster call, people in the country are enjoying a different aural palette. Near grasslands they hear the slurred whistles of meadowlarks on overhead wires. Phoebes and pewees call their own names from savanna and forest. A pileated woodpecker crashes its bill against a tree as big around as a rain barrel. In the forests, yellow-throated vireos repeat endlessly: ee-ay, three-eight! Some 30 bird species, in addition to the city ones I can enjoy, will greet the lie-abed country birder.

What sustains this rich bird spectrum, and how much does it diminish with development? Can we have new homes and businesses without sacrificing the nature that has characterized our region for several thousand years? Such questions had dogged me for a long time. Finally, in 1998, I enrolled as a Ph.D. student at the University of Minnesota and began a study exploring the effect of development on birds.

I started by laying out 300 research plots of 330-foot radius across the northern Twin Cities - a third of them in three nature reserves, another third in three rural townships, and the last batch in three suburbs. For two springs, in 1999 and 2000, several assistants and I counted birds by watching and listening for all the birds that used each plot during 10-minute periods. I then correlated that information with the types and quantities of trees, shrubs, and grasses in the plots; amount of pavement and building surface; distance to roads and buildings; and other indicators of how intensively the land was being used. The goal: to learn which bird species did well (and which did not) when land around them was used in various ways.

During my two-year study, I felt I was swimming just ahead of a crashing wave. Not only did I see new roads being built and old ones widened, but I also saw new homes appear near several study plots. One day I arrived at a plot 20 miles from the nearest dense suburban development and found an attached garage on it. When I asked the owners why they built so far out in the country, they told me they moved from the city because they wanted their children to have the kind of life they'd had growing up in the country.

Who Sings Where?

I study birds because I love having them around. Their diversity also tells us about the state of ecosystems we depend on for clean water, fertile soil, abundant wildlife, and pleasant surroundings. One could say that bird diversity is one measure of our environment and society's well-being.

Between 1990 and 1997, the rural areas in the seven-county metro region had absorbed new single-family homes on about 33,000 acres, an area larger in size than Boston proper. I hoped our research would give a glimpse of the impact of such growth on bird populations.

In fact, our study turned up some dramatic results. The species of birds in our plots differed depending on land use. Oddly, the suburbs supported more individual birds: We counted an average of 23 birds per suburban plot and 16 per plot in "wilder" nature reserves and rural lands. However, we found that the number of bird species in both nature reserves and rural lands exceeded the number of species in suburbs by an average of 30 percent.

Suburban Birds

Our study found some bird species profit from intense development. These development embracers are the regulars seen at feeders and heard in a suburban dawn. Mourning doves, robins, grackles, house sparrows, and cardinals, for instance, take advantage of "suburban savannas" of short grass and pavement with scattered trees, abundant nesting places in evergreens and ornamental shrubs and the nooks and crannies of buildings and other structures, as well as a seemingly limitless food supply.

The same development conditions prevent other species from using the suburbs at all. Ovenbirds, field sparrows, eastern towhees, and several other development avoiders shrink from development. In our study more than a quarter of the bird species of typical farm grasslands were missing from suburban "grasslands" such as sports playing fields. Suburban "savannas" supported an even smaller proportion of the savanna species typical of farm country and nature reserves.

What depresses bird diversity is a lack of variety in habitat types (such as grassland, savanna, and forest) and habitat structure (the various heights of grass, trees, and shrubs). For development avoiders, the vast and uniform suburban landscape means fewer places to nest, find food, and avoid being eaten.

Nature Reserve Birds

Little known but colorful and vocally inspired birds, such as the ovenbird, scarlet tanager, blue-gray gnatcatcher, eastern towhee, blue-winged warbler, and vesper sparrow, find their best homes in nature reserves. They disappear from suburbs and lands with too much agriculture.

Isolation from human endeavor seems important to these development avoiders, but we found some in large suburban forests, especially those far from buildings and roads. In fact, forests in suburbs in our study had as much species variety as forests in reserves and rural lands. The gray catbird, house wren, and downy woodpecker actually fared better in suburban forests than elsewhere in the region.

Rural Birds

Conserving farmlands appears to be key to preserving barn swallows, savannah sparrows, great crested flycatchers, and dozens of other species. These birds are most common in rural areas. They tolerate some development but not widespread and intense suburban development.

Some of the Midwest's most beloved and engaging birds - eastern bluebirds, indigo buntings, and meadowlarks - make rural lands their primary home. So does the less familiar grasshopper sparrow, which keeps in touch with grass-foraging relatives using cricketlike buzzes and twitters. The bobolink, sporting cream and white patches, warns rivals away in a fluttering, bubbling descent from on high. The brown thrasher - a bird with a thousand songs - flashes rusty feathers as it springs up from thickets to look around.

Grassland and savanna birds of the countryside are declining in numbers faster than forest birds are. Since 1966 the U.S. Fish and Wildlife Service has been counting birds along highway census routes. Henslow's sparrow populations are shrinking nationwide by more than 7 percent a year. (If Minnesota had lost people at that rate, our population of 3.6 million in 1965 would have dropped to 245,000 today.) The grasshopper sparrow is losing ground at 3.7 percent per year, and the eastern towhee at 1.9 percent. A sense of alarm is growing among ornithologists nationwide as they watch many bird species lose their habitats and head for the endangered species list.

Rural grasslands and savannas have shrunk not only due to development but also because the rural lifestyle has changed. Fewer farmers raise livestock. Those who do tend to house the animals and feed them grain rather than pasture them. Crops have shifted to corn and soybeans rather than a mix that includes medium-height grasses, which provide grassland bird habitat. Abandoned hay meadows and pastures are turning into thickets and forests.

Yet I take heart from the diverse rural bird community we found in our study. Eastern bluebirds, ruby-throated hummingbirds, and rose-breasted grosbeaks all thrive, in part because of food and shelter humans provide. Although they were not common enough to statistically analyze, we encountered Cooper's and sharp-shinned hawks, wild turkeys, kestrels, northern harriers, sandhill cranes, and other large or wide-ranging birds in rural areas around the Twin Cities.

Slow Loss

I suspect the changes in bird life are going largely unnoticed. If birds dropped out of trees with each new house, there might be an uproar against construction just as there was against DDT when dead robins dropped onto lawns 40 years ago. But species loss due to habitat loss and simplification is slow, incremental, and inconspicuous.

If we want diverse bird life, we must protect habitat as our area develops. Then, instead of just watching backyard birds, people could bike or walk to places where they could see and listen to birds such as an eastern towhee, whistling Drink-your-tea! A landscape that shelters a diversity of birds will be like a bank account that funds cleaner water, healthier soil, more wildlife, and greater recreational opportunities. And on top of it all, we will hear bird song, vibrant and various.

Kim Alan Chapman, St. Paul, is a teacher and an ecologist with Applied Ecological Resources, an ecological restoration and management company.