Advisory: No birds were harmed in the reporting of this article.

The tiny yellow-rumped warbler, having been weighed, measured and banded, was ready for its big test.

William Haffey, an ecology graduate student at Fordham University, cradled the nervous clump of gray and yellow feathers in his hands and carefully released it into a long, dark tunnel. At the far end were the adjacent glass panels, illuminated by a daylight simulator.

One panel was familiar transparent glass, which contributes to the demise of hundreds of millions of birds who fly into it each year in the United States. The other was bird-friendly glass, featuring white vertical stripes that are supposed to serve as a kind of avian stop sign.