The victim’s body was still warm when Linda Saucerman scribbled a quick death certificate on the front of a plastic bag: “Scarlet Tanager, Male, 9:40 a.m., September 27, Morgan Mail Facility.” She then sealed the bird inside.

As more than 200 bird species pass through New York City on their journey south for winter, many will have their trips cut short by a killer they never see coming: glass windows.

Mrs. Saucerman is a volunteer for Project Safe Flight, a program of the New York City Audubon Society, and she has filled the organization’s freezer with many such plastic bags. In some patrolling areas, volunteers find hundreds of dead or injured birds each autumn, nearly all of them migrants.

“Sometimes the society isn’t open, so I’ll have to bring them home.” Mrs. Saucerman, a 34-year-old freelance writer, said. “I had 10 birds in my freezer at one point. I had to stop because there was no space for food.”

To reduce the frequency of deaths by collision during migration seasons, the NYCAS has teamed up with the U.S. Fish and Wildlife Service and a professor of ornithology at Muhlenberg College in Allentown, Pa., Daniel Klem Jr., to conduct the first-ever study on such accidents in an urban setting.

The study, which surveys 80 sites across New York City, will attempt to determine what combination of conditions, such as types of glass and levels of nearby vegetation, lead to the most bird collisions.

“If a migrant wants safety in a crowded urban area, for example, it might try to fly to the first tree it sees,” Dr. Klem said. “And many times, that tree is a reflection.”

Chelsea’s Morgan Mail building is an attractive pit stop for migrant birds, in part because of the athletic field across the street and the trees that line its exterior.

“I think the study will show that vegetation has to be a huge factor,” Mrs. Saucerman said. “If it was just windows, we’d be stepping over birds all the time.”

This threat to birds caused by the combination of vegetation and glass lies at the root of Richard Podolsky’s two-point approach to helping architects design a bird-friendly Freedom Tower: He favors oddly shaped windows and a limited number of plants. An industrial ornithologist, Dr. Podolsky was consulted by Silverstein Properties because there was a high rate of bird deaths at the former twin towers.

The Freedom Tower’s primary defense against bird collisions will be wavy, nonreflective windows on its bottom 200 floors.

“This built-in feature will make crashes virtually impossible,” Dr. Podolsky said.

Although developers have yet to determine the landscape around the Freedom Tower, Dr. Podolsky said controlling the vegetation will be half the battle against bird collisions. He suggests that to discourage migrants from landing in the area, architects should plant trees and flowers that do not provide fruit or food.