Residents of Wisconsin are being encouraged to switch off outdoor lights on the night of September 24 to help safeguard millions of birds flying across the state.

According to a press release from Save Our Songbirds, a conservation organization, an enormous wave of bird migration is anticipated, with approximately 21 million birds passing through Wisconsin overnight. The statewide Lights Out Alert recommends that homes, businesses, and municipalities turn off unnecessary outdoor lighting from 11 p.m. to 6 a.m.

The release explains that most birds migrate during the night, and artificial lights can confuse them, luring them into urban areas where they face increased dangers, notably from collisions with windows.

Craig Thompson, a co-founder of Driftless Birds, a nonprofit dedicated to bird conservation in Wisconsin’s Driftless Area, says, “Twenty-one million birds will be migrating through Wisconsin overnight on Sept. 24, and scientists have issued a Lights Out Alert for nearly the entire state. We urge everyone to help protect our birds by turning off nonessential outdoor lights.”

Research indicates that glass collisions cause billions of bird deaths each year in the U.S., contributing to the loss of nearly 3 billion birds in North America since 1960.

The Alerts are provided by Purdue University’s AeroEco Lab, which utilizes radar and forecasting tools to monitor migration. In addition to the statewide alert for September 24, smaller alerts are scheduled for eastern Wisconsin on September 23 and for eastern and northern regions of the state on September 25.

Bird groups across Wisconsin are also encouraging residents to reduce light pollution and make homes safer by treating windows with screens, decals, or parachute-cord curtains that help birds recognize glass.

Turning off nonessential lights not only helps protect wildlife, advocates say, but also helps save energy, reduce costs, and preserves the night sky.