About 25 volunteers searched for birds Saturday, from early morning until sunset, said Annette Prince, the group’s director. The organization’s hotline for reports of injured birds was ringing roughly every 30 seconds at one point, she said.

“We’d pick up a bird at a building, go around that building, and immediately find another,” Prince said. “We had birds hitting the glass windows over our heads.”

The count followed a major migration night: more than 5 million migratory birds were estimated to have passed through Cook County on Friday, Oct. 16. October is the migration’s peak, and Chicago lies along a major North American route.

The number of birds collected is not a complete measure of the toll. Many may have been missed, Prince said. Dead birds were taken to the Field Museum for research, while injured birds went to the DuPage Wildlife Conservation Center, which reported receiving more than 250 birds on Saturday.

The collisions highlight the risks glass buildings pose to migrating birds. Glass that reflects trees or sky can appear to be open space; textured glass and other visible treatments can help birds recognize a barrier.

Chicago developers currently can choose whether to add bird-safe features to new buildings. Advocates are pressing the City Council to require protections for certain new construction and major renovations. New York City, San Francisco and Washington, D.C., have adopted similar laws, Prince said.

A local example suggests such measures can make a difference: after more than 1,000 birds struck McCormick Place’s Lakeside Center in one night in 2023, bird-safe film was installed on its windows. Collisions later fell sharply, according to the monitors.

Prince said the weekend’s losses underscored the need to make safer passage part of how Chicago builds. “Chicago can have beautiful buildings and beautiful birds, and they can all coexist,” she said.