A Perilous FLIGHT

American Forests, Autumn, 2000 by Karl Blankenship

Rising out of Chesapeake Bay, Hart-Miller Island seems an unlikely hot spot for birds. Most of it is ringed by a 44-foot-high dike to hold mud dredged from Baltimore shipping channels. The mud is pumped inside giant dikes where it slowly bakes in the sun. Flocks of migrating shorebirds pause to pull worms from the drying sediment.

The island is known for its huge diversity of gulls, sandpipers, and terns. But it is also a popular place for migrating forest songbirds, which find sanctuary within its few acres of trees on their trip north. "Sometimes, the woods are full of warblers," said Gene Scarpulla, of the Maryland Ornithological Society, who monitors birds on the island. "It's a stopover place for them."

Once, some of these birds ended their long journeys just a few miles away, on the mainland. Now, few bother. Scarpulla's records show island sightings of many forest-dwellers, such as ovenbird, orchard oriole, hooded warbler, and others, that will stop for a break on Hart-Miller but wouldn't think of building a nest across the water in the rapidly developing Baltimore Washington corridor.

Wooded areas that surrounded the Baltimore-Washington region only a few decades ago have been cut down, paved over, or chopped into ever-smaller pieces to make way for homes, malls, and highways. The large blocks of forests that once offered nesting sites for birds now spell peril as they are overrun by cats, blue jays, and other predators attracted by the changing habitat. It is, in the words of one ornithologist, a "black hole" for forest-nesting birds.

A recent Regional Ecosystem Analysis by AMERICAN FORESTS illustrates why. Using satellite images to measure land-use changes, it showed that overall tree cover in the Baltimore-Washington area declined from 51 percent to 39 percent between 1973 and 1997. From a forest bird's perspective, things are worse. The analysis revealed that heavily forested areas--places with more than 50 percent tree cover--declined at an even faster rate, from 820,569 acres to 555,090, a 32 percent drop. Not only is the region losing trees overall, but blocks of woods are becoming smaller and increasingly isolated.

Nor are concerns limited to the Baltimore-Washington corridor. For nearly two decades, many birders have worried about the health of migratory bird populations inhabiting the nation's forests. North America has about 250 species of "neotropical migrants," birds that winter in the tropics but fly huge distances to more temperate climates to build nests and rear young. About two-thirds of those long-distance migrants are forest-dwelling birds.

These birds move not because of temperature but for food. They go north to harvest the crop of worms and bugs from the forests each spring, food they will use to rear their young. They retreat south as food becomes scarce. It is a mutually beneficial relationship for birds and forests: Some have estimated the forest-pest control value of birds at $5,000 an acre.

But no meal is free, and birds pay a high price for their forest banquet. Migration, always perilous, is becoming more hazardous all the time. The migration path for most eastern birds hugs the Atlantic coast, one of the most rapidly developing parts of the country. Along the route, new buildings, communication towers, and other flight hazards are going up in front of the birds, which migrate mostly at night. Safe wooded stopover sites, where they can rest and refuel before continuing their flight, are increasingly scarce. That's one of the reasons AMERICAN FORESTS has funded a local conservation group, the Alliance for the Chesapeake Bay, to expand the Hart-Miller Island forest by planting an additional 20,000 trees (see sidebar, page 37).

Worries don't end with the migration. Scientists are finding danger signs in forest destinations, Alarm bells began going off in the late 1980s when some studies suggested that forest-dwelling neotropical migrants were in widespread decline. As woodlands and neighborhoods lost their warblers and tanagers, some even warned of a new "silent spring"--a reference to Rachel Carson's groundbreaking book on the dangers of pesticides and insecticides.

New research suggests those early warnings were overstated. Red flags initially flew in large part because of the public perception around places such as the Washington, DC, region that backyards and small parks had grown strangely silent. And, indeed, surveys show those places are remarkably barren of birds. Many urban and suburban areas are so filled with hazards and predators it's unlikely any nesting bird will successfully rear young. But a decade of analysis has resulted in a much different, albeit murkier, overall picture for forest birds. In fact, most forest bird populations are in good shape. (As a group, grassland-dwelling birds tend to be worse off--it appears nothing is less secure today than a piece of idle land.)

But all is not well in the woods. While overall populations of many forest dwelling species are stable or increasing, several have suffered serious declines. In the past quarter century, the North American Breeding Bird Survey--the main source for bird population trends--has documented a 51 percent decline in the cerulean warbler, a 48 percent decline in the olive-sided flycatcher, a 41 percent drop in the wood thrush and a 34 percent drop in the Eastern wood-pewee.