At first glance, not much seems remarkable about the blackpoll warbler, a black and white songbird that measures 5–6 inches long and weighs little more than an ink pen.
But it’s what you don’t see that makes blackpolls remarkable. Beginning late each summer, the birds start moving southward from their boreal forest breeding grounds, which range from northern Pennsylvania through much of Alaska.
Bit by bit, they make their way to the Atlantic Coast between New England and the Delmarva Peninsula. Then, in one giant leap, they head south over the Atlantic Ocean, not stopping until they reach the Caribbean Islands or northern South America.
It’s a flight that can take them 2,000 miles over open water, flying nonstop for three or four straight days. By the time they complete their trip, they’ll have lost a fifth of their weight. Still, for a trip that requires an estimated 3 million flaps of their wings, that’s not bad: A pair of researchers calculated that if cars were as energy efficient as blackpolls, they’d get 720,000 miles to the gallon.
Each year, about 40 percent of all birds migrate, but the proportion of migrating species increases in northern areas. These birds came north in the spring to take advantage of abundant food supplies vital for them to breed and rear their young. Forest-dwelling birds arrive in time to catch the peak insect and caterpillar season. Eagles show up along tidal rivers along the East Coast to coincide with the spring spawning runs of migratory fish such as American shad. Birds return south as food supplies decrease.
While the blackpoll is the migration champ among small songbirds, others also journey thousands of miles each year. Globally, the arctic tern has the greatest migration, traveling between the Arctic and Antarctica, taking advantage of the summer season in each. But some birds migrate short distances; blue jays from the mid-Atlantic may hop just a few states to the south, only to be replaced here by some that have ventured a few hundred miles from the north.
The Atlantic Flyway, the corridor used by many birds that breed over a wide expanse to the north, condenses to a narrow funnel as it reaches the mid-Atlantic. So the region is a hot spot for migration. It is the southern destination for some northern-dwelling birds, including many types of waterfowl, and the winds along the region’s mountain ridges help propel the movements of soaring, broad-winged raptors, especially hawks.
Nowhere is the funnel more evident than on the Delmarva Peninsula, where migrating birds are squeezed between the Atlantic on one side and the Bay by the other. “We’re sort of in the catbird’s seat here, in terms of migration,” said Bryan Watts, director of the Center for Conservation Biology, a research unit shared by Virginia Commonwealth University and the College of William and Mary, who has studied migrating birds on the peninsula for years. “This is probably one of the best places on the continent to observe migration, and it is an accident of geography.”
The impact of that geographic accident is especially notable at the peninsula’s southern tip, where songbirds, which mainly migrate at night, seek a place to land before continuing across the mouth of the Bay. There, in the final couple of miles of land, huge numbers of resting songbirds frequently cram into trees and shrubs.
Kiptopeake State Park and Eastern Shore of Virginia National Wildlife Refuge have some of the greatest densities of fall migrants found anywhere.
But you don’t have to be along the coast to see migrations. For songbirds, Watts said, young birds tend to follow the coast as they head south, using the geography as a navigation aid. Older birds tend to fly a bit farther inland, where they find more mature woodlands with more insects to fuel their journey.
While some of the most dramatic migration scenes may play out at geographic bottlenecks, migration is something people can experience anywhere — even if one can’t see the birds. Most songbirds migrate at night but often move in such huge numbers that on a clear night with a north front moving through, people can hear what they can’t observe. “Sometimes there can be millions of birds going over, and you can hear them calling,” Watts said.
Indeed, it’s not just geography that influences migration. Weather, particularly cool, dry fronts from the northwest help to propel birds along their fall flights, providing them with an energy-conserving tailwind. Birds amassed on the ground will take flight and disappear overnight as the front moves through.
The right wind is especially important for soaring birds such as hawks. It’s been estimated that a broad-winged hawk would expend its pre-migration fat stores in just five days of flapping its wings during flight. By catching the right drafts, it can fly for 20 days — enough to take it 3,000 miles to the tropics.
Hawks also offer people a unique visual experience. Unlike songbirds, they predominantly migrate during the day, when they can catch the strongest thermal drafts as temperatures warm. “In terms of things in the act of migration, seeing the hawks streaming by is an amazing sight,” said Gwenda Brewer, science program manager with the Maryland Department of Natural Resources Wildlife and Heritage Service.
Migration has fascinated people for millennia — there are references to migrating birds in the Old Testament.
Over time, scientists have unraveled some of the secrets of how birds find their way to locations thousands of miles distant each year, using cues from the sun and stars, the Earth’s magnetic field, landmarks and instinct to help guide their journeys — often made at altitudes of 20,000 feet or more.
Still, there’s a bit of mystery left in understanding the flights made by species such as ruby-throated hummingbird, which are so petite one could mail five large ones with a single, first-class stamp. Yet after they spend the summer breeding in woodlands and backyard gardens here, they fly south, cross the Gulf of Mexico, and winter in southern Mexico and Central America.
“You look at them, and they are just these tiny little things, and they fly across the Gulf of Mexico — maybe taking more than 20 hours at a shot to do so,” Brewer said. “To imagine that little bird flying for so long is really impressive.”
Where the Birds Are (Hint: There’s a Place Near You)
Even close to home, there are opportunities to glimpse the grandeur of fall migration — if one knows when and where to look.
Shorebirds migrate south in July and August, and many songbirds migrate from August through early October. Hawk migrations reach their peak in September and October, but extend into early November. Waterfowl, many of which come to the Bay region to spend the winter, reach their peak migration in late October and November.
Weather is an important component of bird migration, as heavy periods of fall bird migrations track with cold fronts coming from the north.
To take some of the guesswork out of when to look, visit www.birdcast.info, operated by the Cornell Lab of Ornithology. It provides weekly migration forecasts based on the time of year and anticipated weather patterns.
Here’s a sampling of some places noted for bird migrations. Many offer public programs with migration themes.
- Eastern Shore of Virginia National Wildlife Refuge and Kiptopeake State Park are major hot spots throughout the late summer and fall for various kinds of migrating birds, from songbirds to hawks to waterfowl.
- Farther up the Delmarva Peninsula, Chincoteague National Wildlife Refuge and Assateague National Seashore are also good spots to see a variety of migrants, especially shorebirds in late summer.
- Songbirds mostly migrate at night, but parks with large forested tracts can have increased abundances of songbirds during migration season. Try Swallow Falls State Park or Green Ridge or Savage River state forests in Maryland.
- Areas that have large water barriers, such as the north side of the Potomac River, can also build up bird numbers during migration season. New Point Comfort Natural Area Preserve, on the north side of Mobjack Bay in Virginia, has a reputation for large numbers of migrating songbirds.
- Urban areas can also be surprisingly good for viewing migrations, especially those of songbirds. Large wooded parks are an oasis for migrating birds in a sea of development. Check out Cylburn Arboretum or Patterson Park in Baltimore, or Rock Creek Park in the District of Columbia. Also, nature centers in urban parks may have programs focused on migration.
- Hawk Mountain Sanctuary, near Hamburg, PA, has a well-deserved reputation as a location to see both large numbers, and a wide diversity, of migrating raptors.
- The Hawk Migration Association of North America collects data at designated Hawk Watch sites throughout the nation, dozens of which are in the mid-Atlantic region. Its website, www.hmana.org, offers a map with directions to all sites, a listing of the types and numbers of raptors that have migrated in past years, and when they typically pass by. Many Hawk Watch sites are located at state parks such as Kiptopeake State in Virginia or Elk Neck, Washington Monument or Fort Smallwood state parks in Maryland, or at nature centers. Such parks and centers often offer programs related to hawk migration, especially on weekends.
- Blackwater National Wildlife Refuge is a good place to see many types of migrating birds throughout the fall, but is most noted for its waterfowl. Mattawoman Natural Environmental Area, a state-owned tract in Maryland’s Charles County, is a good place to see migrating ducks in the fall, as is Deale Island Wildlife Management Area and Eastern Neck National Wildlife Refuge, on the Eastern Shore. In Pennsylvania, Middle Creek Wildlife Management Area, near Kleinfelterville, is a focal point for waterfowl migration in both fall and spring. Further west, Rocky Gap State Park in Maryland can have a good abundance of migrating waterfowl.