It takes biologists Tim Keyes and Lee Sexton only a few seconds to find the first victim: a hummingbird that probably was headed for the Gulf of Mexico before it slammed into an office tower.

Since August, they have scoured the grounds of swank hotels, high-rise condominiums and ritzy corporate buildings, trying to track how many birds are victims to Atlanta's architecture.

Ornithologists estimate that millions of birds die each year from colliding with man-made hazards. In trying to determine how best to prevent these crashes, the researchers are studying how -- and possibly why -- the birds are flying into the structures.

Different factors can be blamed. At night, high-flying birds are drawn by the glow of lighted buildings. In the daylight, the reflection of vegetation on glassy panes is a culprit. Carefully manicured greens and lush landscaping also lure birds into inescapable concrete jungles, and trees and plants inside windowed lobbies and office entrances are enticing.

"Birds don't recognize glass as a hard surface," said Michael Berger, director of bird conservation for New York's Audubon Society. "They either see through the window or see a reflection."

Some building managers and cities have taken steps to try to curb the problem. In downtown Atlanta, dead birds piling up outside the lobby of a government building with vegetation and fountains prompted the building manager to put up a replica of a predator to try to ward off birds.

In Chicago, building managers are encouraged at night to turn off the lights, saving an estimated 10,000 birds each year in the city. Besides promoting the lights-out policy, members of the Chicago Bird Collision Monitors run a local hot line to rescue injured birds.

Annette Prince, the group's associate director, tells of two adjacent buildings, both with glass lobbies, where one goes dark each evening and the other remains lighted. Volunteers have found droves of dead birds around the building that keeps its lights on, and only a few around the neighboring, dark structure.

The New York City Audubon Society also has started Project Safe Flight to encourage building managers to darken skyscrapers at night and architects to use new types of patterned glass that birds can recognize. Volunteers have documented about 4,000 birds killed or injured by building collisions at a few buildings in Manhattan since 1997. Their survey listed about 100 different species as victims.

"Our goal is to develop a glass that birds can see but people cannot," said E.J. McAdams, the group's director.

As she picks up each dead bird outside an Atlanta building, Sexton tries to determine what caused the fatal crash. Mirrored glass windows? Vegetation inside a windowed atrium? Bad weather?

She rises early to check the buildings long before the city's many commuters start heading to work.

Some days Sexton finds more than a dozen dead birds. She puts each one in a plastic bag in an ice cooler in her trunk. A few are so badly damaged that she needs Keyes's help to identify them.

Keyes, a biologist for the Georgia Department of Natural Resources, unfurled one decaying mass of feathers, spreading its wings to try to identify it. "This is a mess," he said.

A few minutes later, the two researchers found several more misshapen corpses.

"This building has really interesting birds," Sexton said. "There's always a different type."

She stopped for a moment to give the bird-filled plastic bags she is carrying a quizzical look.

"I've been doing this too long, haven't I?"

In Atlanta, biologists Lee Sexton, left, and Tim Keyes collect a dead bird. They scour the grounds of high-rise structures in the city for feathered victims.