An Astonishing 17.6 Million Birds Just Flew Over Wisconsin At Once

Every spring, one of nature's most remarkable events plays out largely unseen, high above our heads. Hundreds of millions of birds make their way north across the United States, navigating by stars, magnetic fields, and the landscape below, and they do most of it in the dark.

That's what makes artificial light such a serious problem for migrating birds. Experts say about 80% of migrating birds fly at night, and the glow from outdoor lighting can disorient them, pulling them off course and into urban areas where they face real dangers, particularly windows and buildings.

Window collisions alone are estimated to kill up to 3.5 billion birds annually in the United States, and researchers point to light pollution as a major factor in the nearly 30% decline in North American bird populations over recent decades.

Get our free mobile app

The scale of what happens during peak spring migration is staggering. On the night of Monday, May 11, 2026, researchers with the Cornell Lab of Ornithology and Purdue University used weather radar to predict that approximately 17.6 million birds would fly over Wisconsin in a single night. Nationwide, an estimated 383 million birds were expected to migrate across the lower 48 states that same evening.

What A Lights Out Alert Means

When migration forecasts reach that level, the Cornell Lab and Purdue University issue what's called a Lights Out Alert, a statewide call for residents, businesses, and municipal officials to turn off non-essential outdoor lights from 11 p.m. to 6 a.m.

Lights Out Wisconsin, formed in the fall of 2025, coordinates those alerts statewide and was behind Monday night's call to action.

Lights Out Alerts are only issued on the top 10% of highest-migration nights, which collectively account for roughly half of all seasonal migration traffic. In other words, those peak nights matter enormously for the birds passing through.

In Wisconsin, alerts are available for Appleton, La Crosse, Madison, and Milwaukee, among 216 cities nationwide tracked by the BirdCast Migration Dashboard. If you live outside those cities, you can sign up for alerts from the nearest metropolitan area.

Peak Migration Season Runs Through Mid-June, And You Can Still Help

Monday night's massive flight doesn't mean the migration is over. Peak spring migration in Wisconsin typically begins during the first week of May and runs through mid-June, with northern parts of the state seeing it slightly later. There will be more high-migration nights before the season winds down.

The Wisconsin DNR recommends the following ways residents can support migrating birds throughout the season:

• Turn off non-essential exterior lights at night, especially during May and early June
• Reduce window collisions by using external screens, markers, or cords on windows
• Plant native fruit-bearing trees and shrubs such as serviceberry, dogwood, and cherry to provide food and cover
• Avoid pesticides to protect insect-eating birds, including many common backyard species
• Provide clean water and native seeds to help fuel birds on their long journeys north

SEE NOW: The Best Small City To Start A Business Right Now In Wisconsin

It's a simple ask: Turn off the porch light for a few hours, and the payoff for the birds passing over your yard tonight could be significant.