Millions of tiny, neo-tropical songbirds fill the skies over Virginia's Eastern Shore during spring and fall migrations. Yet, most people are in the dark, quite literally, when it comes to picturing this amazing, natural phenomenon. Because these enormous flocks take flight only after sunset, they remain almost invisible. A network of ornithologists, guided by the Nature Conservancy, is shedding new light on these birds' migratory patterns using state-of-the-art N-POL radar from NASA.

About a year ago, searching for a site roughly midway between existing radar facilities at Wallops Island and Wakefield, NASA happened upon Oyster, where the Conservancy owns Cobb Island Station and some 1,400 acres around the harbor. While NASA scientists are using the radar to advance their study of rainfall, the Conservancy and a group of researchers are using the radar to identify the sites migratory songbirds depend on for resting and feeding.

"This is the most sophisticated radar ever available for bird research," says Barry Truitt, the Virginia Coast Reserve's chief conservation scientist. "This project has the potential to advance the whole science of radar ornithology."

The nationwide NEXRAD radar system, the familiar Doppler radar from television reports, depicts patterns of targets—whether rainstorms or flocks of birds—and can determine flight direction and velocity. Truitt says he quickly realized that if the new N-POL system at Oyster could measure the size of individual raindrops, it should also be able to calibrate the size of individual birds. If so, then researchers could now use radar to delineate songbirds from larger species.

Truitt explains that cold fronts tend to trigger a mass exodus of songbirds that then take advantage of prevailing tailwinds. Shortly after sunset, when the songbirds begin to ascend, they circle around and around, gaining altitude before striking off toward their ultimate destination.

As signals emitted from the radar tower bounce off the birds and return to the antenna, computer software creates onscreen loops that show the movement in swirling patterns of vivid color. With only a little imagination, suggests Truitt, "The sky looks like a river of birds."

Information gleaned from the radar will guide the Virginia Coast Reserve's future protection and restoration work on the Eastern Shore, helping the Conservancy use its resources most efficiently. In addition, field research partners are capturing and banding birds at ground level, helping to validate data as well as determining the types of habitat beneath the birds' radar "exit signatures."

"I think we'll see the radar confirm the importance of the southern tip" of the Eastern Shore, Truitt predicts, "but it'll open up whole new worlds."

For more information:

• The Nature Conservancy in Virginia
  Together with our members and conservation partners, The Nature Conservancy has protected more than 250,000 acres of critical natural lands in Virginia.
• Places We Protect: Virginia Coast Reserve
  The Virginia Coast Reserve is a coastal wilderness that includes beaches, maritime vegetation, forests and salt marshes.
• Online Field Guide: Virginia Coast Reserve
  Across the Chesapeake Bay from Virginia’s mainland, the tip of the Delmarva Peninsula forms a narrow finger of farm field and salt marsh laced with tidal creeks, mud flats, shallow bays and ponds.

Find out how The Nature Conservancy is working to protect migratory birds:

• Conserve the grassland birds of the Great Plains of North America
• Study climate change in the Great Plains and its effect on bird populations
• Identify and protect a network of high-quality migration stopover habitats around the Gulf of Mexico
• Conserve migratory birds on the Pacific Coast of North America
• Examine the wintering ecology and habitat requirements of Kirtland's Warbler
• Study the Cerulean Warbler, one of the fastest declining species of migratory bird
• Delve into the Pine-Oak Forests of Central America to conserve this critical habitat for birds

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Photos: Eastern Bluebird in Kittatinny Valley State Park, New Jersey, USA. Photo © Lynn K. Groves, www.lkgphotography.com; Royal Tern, Morro Strand State Beach, California, USA. Photo © Mike Baird (Creative Commons).