Why do birds migrate in the fall? Do any migrations come through our area?
-Lou Niko, Asheville, N.C.

Avian migration is a natural extension of the exquisitely practical adaptation of flight. When it's possible to fly to the top of a tree to escape a predator or to find the last ripe berry at the end of a limb, then taking wing for a distant locale is an evolutionary no-brainer. Sometimes, migration is a few hundred miles; sometimes it's thousands of hemisphere-spanning miles each way.

We are suitably impressed when human athletes, such as long-distance bicycle racers or Olympic marathoners, push their bodies to the extremes of endurance. Yet, most of us don't notice when migrating birds-not much more that a few ounces of feather, hollow bone, and instinct-make their astounding journey year after year. Lance Armstrong may have won the Tour de France six times, but the blackpoll warbler flies thousands of miles each autumn from New England to South America. A human athlete would have to run a four-minute mile for 80 hours to match the amount of energy expended by the tiny bird as it stays aloft over the Atlantic for 80-90 continuous hours.

Birds that breed in North America in the spring and summer, then fly south as the fall days shorten and slide into winter, are called neotropical migrants. There are around 150-200 neotropical migratory species, which include songbirds, shorebirds, waterfowl, and raptors. "South" can mean anywhere in Mexico, Central America, South America, or the Caribbean islands.

Environmental cues such as day length and temperature trigger complex internal clocks just before the fall leg of their biannual round trip. In essence, the birds know instinctively that their food is running out and it will soon be too cold to survive. So like all good athletes, they start to bulk up, increasing their fat reserves by up to 10 percent per day to fuel the long trek south. Insectivorous birds switch to fruits and berries to maximize their fat load. Some species increase their body mass by as much as 100 percent. When the time comes, they steer by the stars of the night sky, the setting sun, and major topographic features.

Most commuters know that there are generally just a few ways to get to their destinations. Migrating birds are no different, funneling into four major southbound routes, or flyways. They are the Atlantic flyway, the Mississippi flyway, the Central flyway, and the Pacific flyway. Most birds in our area migrate along the Atlantic flyway, but in the far western reaches of Virginia and North Carolina, one might observe the Mississippi flyway in action. Corridors threaded within these avian superhighways follow rivers, valleys, mountain ranges, and coastlines. Hawks and other raptors tend to follow the mountains, taking advantage of warm updrafts to air their sweeping, soaring flight. Shorebirds, naturally, stick close to the shore, while waterfowl do the same, but also use broad expanses of the great tidal rivers that wind their way to the ocean.

Migratory songbirds tend to distribute themselves throughout the Atlantic flyway, but the heaviest concentrations are found along the shoreline. These small migrants often fly at night to take advantage of cooler temperatures, calmer winds, and fewer predators. They fly at heights as high as 6,000 feet, but most range between 500-2,000 feet. Some fly as fast as 30 miles per hour.

All migrating birds need to take breaks to rest, feed, and hide from predators. These so-called "stopover" sites are very important to successful migration. Stopover sites can be wetlands, thickly wooded areas, or areas rich in food. Stopover sites tend to be clustered on either side of great natural barriers. Two of the largest barriers in the Atlantic flyway are the open water of the Delaware and Chesapeake Bays. As a result, migratory avian traffic bottlenecks along the narrow Cape May and Delmarva peninsulas as birds seek places to rest, feed, and wait for fair weather or a good tailwind.

Despite the many advantages of migration, it can be a hazardous journey. Most estimates give all migrants about a 50-50 chance of surviving the roundtrip to breed in the spring. Predators and bad weather take their toll, but so do myriad other things, from collisions with tall buildings or car windshields, to hunters and even kids with BB guns. But by far the greatest threat to neotropical migrants is continued fragmentation and loss of habitat. With less and less food and cover available, birds are forced to fly farther on leaner fuel reserves, adding stress to the trip and increasing the likelihood of mortality along the way. It's no secret that many songbird species are declining. And breeding or overwintering habitat loss in the Canadian Arctic or Central and South American rainforest is not necessarily causing numbers to fall. Increasingly, the focus is on losses right here at home. Maintaining the quantity as well as the quality of stopover sites along Virginia's Eastern Shore, the North Carolina coast, and inland areas of the Atlantic flyway, is crucial. Development decisions made on local, regional, and national levels can seriously impact migratory birds. On a personal level, as a homeowner or landowner, one can make bird-friendly landscaping decisions that turn a piece of property into a haven for weary travelers. Such a choice is ultimately better for the soul-for it's far better to wake to bird song than it is to silent skies.

Charlottesville’s William Cocke is always turning over rocks and rotten logs to see what’s underneath. As a young Boy Scout, he learned that cedar bark makes good tinder and four-of-a-kind beats a full house. He also remembers the Camp-o-ree where he had to kill a live chicken and cook it for dinner. He was not traumatized in the least and has no plans to sue. He can be reached at wtc4q@virginia.edu.