Volunteers scoop up birds and bring them to Willowbrook Wildlife Center in Glen Ellyn for rehabilitation and care. They also take thousands of dead birds each year to the Field Museum for documentation and research.

Prince said more birds migrate in the fall because offspring born in northern nests join their parents on the journey south. Real-time bird migration numbers can be found online at BirdCast.info, using weather surveillance radar techniques.

To help mitigate collisions, over two years ago Gov. J.B. Pritzker signed the Bird Safe Buildings Act, requiring the implementation of bird-safety features in construction and renovation of state-owned buildings in Illinois. But these efforts don’t make older buildings safer, Prince said.

“Still, we’re hopeful that at least going forward, we’ll have a safe standard of building … that gives birds a chance to avoid dangerous glass areas,” she said.

Ward has been interested in bird migration since observing his dad watch birds in his backyard near Jacksonville.

“They know where they’re going, and then usually they go back to the exact same spot the next year,” he said. “If you start thinking about how far they go, how fast they go and their ability to actually get to the exact spot they want, it’s a pretty amazing feat.”

A loss of bird species would fundamentally change the way ecological systems in Illinois work, said Ward. Birds feed on decomposing animals and plant matter. They control insect populations. They move around nutrients.

Ward said Chicago residents who have the ability should plant native trees in their backyard — serviceberries, pokeweed and dogwoods. Birds in the fall typically feed on fruit, he said.

“It doesn’t take everyone doing it,” he said. “But if 5% of the population does a little bit more, that will lead to conservation.”

He said he likes to go outside at night and listen to the birds calling to each other as they zip by.